Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: dazz on January 04, 2018, 08:53:12 AM

Title: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 04, 2018, 08:53:12 AM
Hi guys & gals, a n00b here with some questions about my first amp build.
The amp is essentially the application example in the TDA7267A datasheet (http://www.st.com/content/ccc/resource/technical/document/datasheet/bc/22/fd/6e/94/23/42/14/CD00001472.pdf/files/CD00001472.pdf/jcr:content/translations/en.CD00001472.pdf):

(http://i63.tinypic.com/2iuwdnn.png)

I'm also in the process of building a Bazz Fuss V3 pedal (http://www.home-wrecker.com/bazz.html) so I thought I could put that little circuit in the amp to have an overdrive "channel"

(http://i63.tinypic.com/e9ypv6.png)

The idea is to put the Bazz Fuss in front of the TDA7267A and use a switch to bypass it for the  clean channel.
So I have a few noob question for you:

1. The initial plan is using a 12V power supply and a 7809 to get the Bazz Fuss the required 9V. I could use 9V for everything and leave the 7809 out, but would I be losing a significant amount of output by feeding the amp 9V instead of 12V? ETA: I should have RTFM before asking. The answer to this is right there in the chip's datasheet.

2. Do I need all the coupling capacitors from both circuits? Can just use an input cap & an output cap and connect the output of the Bazz Fuss directly to the input of the amp so that when I bypass the Fuzz I leave the input cap there to do it's job? or do I need another coupling cap in between the Fuzz and the amp?

3. For what I could gather, the input impedance of the Fuzz is 1K Ohms while the amp's is 100K. Mentioning just in case there could be an issue there

4. I want to have tone, gain and volume controls. The volume with a logarithmic 50K pot at the output of the amp, the gain with a 1K or 5K pot between the Fuzz's transistor emitter and ground. But I'm not sure what to do about the tone pot. Can I just put a, let's say, 4.7uF and a 68nF cap with a pot in between to implement the tone pot? Or would I be better off trying some of the tone stacks found here? http://monster.partyhat.co/article/amplifier-tone-stacks/

I think that's all for now, any suggestions/corrections appreciated. Thanks in advance
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 04, 2018, 09:31:55 AM
I forgot to mention what I have planned for heat-sinking:

(http://i64.tinypic.com/rwtpic.jpg)

The board is mounted on a 7x4cm aluminium heatsink I cannibalized from a blown PSU. The GND pins of the TDA7267A will be straightened and sandwiched between the board and the heatsink with one or two screws pressing it against the IC pins. Should be enough right?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 07, 2018, 07:18:59 AM
Well, after doing some more research I'm going with a TDA7297 which is more powerful and has two channels. Still not sure about the preamp but I like the Buzz Fuss simplicity. I'll see if I can add a treble/mid/bass tonestack to it
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on January 07, 2018, 08:33:31 AM
Hi Dazz, Regards Tone stacks link;
Be aware that you will need a gain stage to make up for signal loss.
Most of those tone circuits are passive and suffer from insertion loss,, meaning a 1 volt signal swing at the input can be reduced by as much as 70%,,so you will have to make that up with another gain stage.
You will need to do some research and better still make a prototype FIRST. (hint)
An active tone circuit does not suffer insertion loss but they sound a bit different and the classic passive tone circuit were well suited for guitar tone, but both will work ok if done right.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 07, 2018, 08:42:17 AM
Hi Dazz, Regards Tone stacks link;
Be aware that you will need a gain stage to make up for signal loss.
Most of those tone circuits are passive and suffer from insertion loss,, meaning a 1 volt signal swing at the input can be reduced by as much as 70%,,so you will have to make that up with another gain stage.
You will need to do some research and better still make a prototype FIRST. (hint)
An active tone circuit does not suffer insertion loss but they sound a bit different and the classic passive tone circuit were well suited for guitar tone, but both will work ok if done right.
Phil.

Thanks for that great piece of info. I just installed Duncan's tonestack calculator and will definitely prototype it in a bread board to try different configs. I'm thinking maybe the massive amplification capabilities of the Bazz Fuss (MPSA13) might help compensate for some insertion loss here? No idea
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 08, 2018, 05:54:30 AM
Damn, I just can't seem to decide which power amp chip to use. Thought I was settled on the TDA7297 but just came across this little TDA3116/8 beast

https://www.ebay.com/itm/DC-8-26V-TPA3118-PBTL-Mono-Digital-Amplifier-Board-AMP-Module-1-60W-Arduino/162237431824?epid=822273080&hash=item25c61ac010:g:zUUAAOSwLF1X~ykc

But anyway, just read about the importance of power supplies in the stickied thread here so looks like the power amp is the least of my concerns, especially if I'm going to try a power amp that can draw up to 7.5A. This should be a fun project, unless I manage to electrocute myself that is
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on January 08, 2018, 08:05:38 PM
Some advice;
Bazzfuss is an effect ,,not a preamp. So IMO tiss a bad idea for an amplifier circuit.
I'd suggest you build a simple preamp with a tone control then into a power amp.
LM1875 chip will give you 10~20Watts,,depends on PSU.
If more power,, then LM3886 will deliver 30~50Watts, again depends on the PSU ability to supply the grunt to drive the power stage.
If this is your first venture into building these circuits then keep it simple otherwise you will be stuck when something goes wrong.
I learned a long time ago not to build a circuit if I did not know how it worked. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 09, 2018, 04:03:47 AM
Some advice;
Bazzfuss is an effect ,,not a preamp. So IMO tiss a bad idea for an amplifier circuit.
I'd suggest you build a simple preamp with a tone control then into a power amp.
LM1875 chip will give you 10~20Watts,,depends on PSU.
If more power,, then LM3886 will deliver 30~50Watts, again depends on the PSU ability to supply the grunt to drive the power stage.
If this is your first venture into building these circuits then keep it simple otherwise you will be stuck when something goes wrong.
I learned a long time ago not to build a circuit if I did not know how it worked. 8|
Phil.

Yeah, you're right. I'll just keep it simple, modular and relatively low power (something that doesn't involve messing with mains) for my first build and go from there.
I got the idea of using the Bazz Fuss from here http://www.generalguitargadgets.com/how-to-build-it/technical-help/articles/practice-amp-designs/ (http://www.generalguitargadgets.com/how-to-build-it/technical-help/articles/practice-amp-designs/)

Quote
A simple preamp would just be your favorite distortion effect pcb mounted in the same housing with the amp

But anyway, off to read about preamps now. This is not about the quality or power of the amp that results from this, it's about the learning process. Thanks again phatt
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dogbox on January 09, 2018, 02:45:37 PM
Hey Dazz, I'm no expert but I've been mucking around with a similar project i.e chipamp and playing around with various preamps. In my findings I came across a preamp circuit called a Vibin' champ http://www.diystompboxes.com/smfforum/index.php?topic=47371.0 (http://www.diystompboxes.com/smfforum/index.php?topic=47371.0)

Gives a nice clean sound, adds a basic tone control. It's based on a fetzer valve, and has a tone control from an old fender champ. It sounds great.. Currently I'm looking at something with a bit more overdriven sound.

The chipamp that I'm using is AN7522(stereo) and AN7523(mono version). Bought these chips in an electronics hobby store in Malaysia..i think superceded, but you can still get them on ebay easy enough...originally used in TV sets. Great chip if your wanting a lot louder amp than lm386 rubyamp or similar. This thing puts out about 5w from a 12v supply, runs really cool..i don't think i will need heatsink..but will determine when i've finished everything. Tried to get it to heat up by playing it for hours, and it barely gets warm, and I live in Sumatra..where weather is hot. I just using a generic 12v 2A wallwart..so no high voltages to be concerned with.

If I plug straight into the chip power amp I get a very nice clean sound. There's no break up, or overloading..its just dull. I first tried a fuzzface directly into the amp..and it worked but it sounded dull and a little bit bass was missing when i turned one the pots (can't remember which) and the volume lowered. That experiment told me that I needed some kind of gain/recovery stage between the effect and amp..and probably some kind of buffer before the effect such as fetzer/ vibin' champ to give it a bit sparkle.

My next experiment I'm going to have a play around with more of these amp-in-a-box style circuits, with more distortion. Google "wampler black 57" or other similar from runoffgroove.com.

The other thing to remember its one thing to have everything working on a breadboard..but the complexity of the circuit for your preamp can be daunting. more parts/bells and whistles means there is gonna be a lot of work to turn this into a working amp. You will have to learn about creating a schematic, some kind of proto layout, or figure out how to layout a pcb in eagle cad, how to fabricate a pcb or how to order a pcb for fabrication. Fantastic learning excercise, .... but there's a learning curve involved in every decision for us newbs.

I'm going to try my hand at making a pcb for mine. There's trick they use here in Indonesia for doing cold toner transfer using (wait for it) ..mosquito repellent :) https://www.youtube.com/watch?v=4QB1PvV0CXA&t=502s (https://www.youtube.com/watch?v=4QB1PvV0CXA&t=502s). I think theres some ingredient in the lotion that breaks down the toner (maybe alcohol or acetone or both...or it could even be the DEET they use in these products??) that allows the toner to be rubbed off the paper and deposited directly onto the blank copper board...little bit of a knack but looks pretty easy to do. Theres a few of these vids on youtube..you won't understand what the guys are saying..but you can follow pretty easily. Indonesians are ingenious little buggers, and electronics is still hugely popular hobby/occupation and basically people are poor so still repair most stuff..they can't afford the luxury of throwing away electronics when they break (like they do in my home country in Ozzie, and other places in the west like Europe and the USA).

Anyways, hope some of this helps. Give us an update of how your amp progresses.. I will do the same.
cheers
Steve




Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 09, 2018, 06:19:26 PM
Thank you Steve, of course that helps, a lot
I've been googling for preamps and found this one (http://www.diystompboxes.com/analogalchemy/sch/v4preamp.html), but that Vibin looks much simpler.
I plan to use vero-boards. We'll see if I can pull this off

Let us know how your project goes!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dogbox on January 10, 2018, 09:53:05 AM
Actually Dazz that one looks pretty good. Geussing you could put in 10k pots to adjust bias to 4.5v or use your ear..then measure and swap out for single resistor when circuit is stable. I think i might breadboard this one up. cheers for the tip
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 10, 2018, 12:36:28 PM
The section labeled "3x stages" is supposed to be replicated 3 times in series, right?

(http://www.diystompboxes.com/analogalchemy/sch/v4preamp.gif)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 11, 2018, 07:32:28 AM
I have another question if that's OK

The TDA7297 is limited to 2A in it's output. It's input impedance is 30K. So I'm wondering if I can parallel the inputs & outputs to achieve 4A in the output and perhaps be able to drive 4 Ohm speakers? The input impedance would half to 15K. I've read it needs to be some 20 times higher than the preamp's output impedance. Could this reduced poweramp input impedance be an issue?

I guess that's two questions  :cheesy:

ETA: found this: http://www.audiocircle.com/index.php?topic=125202.0
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dogbox on January 11, 2018, 07:55:32 AM
The section labeled "3x stages" is supposed to be replicated 3 times in series, right?

(http://www.diystompboxes.com/analogalchemy/sch/v4preamp.gif)

 Yeh.. http://www.diystompboxes.com/analogalchemy/   theres a link to the original vulcan pedal...it's basically 3x stages of that which he inserted. The cool thing is you could try 1/2/or 3 stages..see whats needed. you could also insert a a jfet version of the vulcan in there, or pretty much whatever you want, for a distortion channel.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 11, 2018, 08:17:44 AM
Thanks again Steve, much appreciated.

Found this thread about the JFET Vulcan and it sounds great http://www.diystompboxes.com/smfforum/index.php?topic=67677.0
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on January 11, 2018, 09:19:43 AM
Again remember it's an effect,, you still need a preamp with a tone control. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 11, 2018, 09:29:54 AM
Again remember it's an effect,, you still need a preamp with a tone control. 8|
Phil.

Thanks phatt, but I'm at a loss. According to this, it's a preamp: http://diystompboxes.com/analogalchemy/sch/v4preamp.html

"A nice 4-stage preamp for guitars with a tube-like sound. Output impedance is low for use with typical solid-state amplifiers. Based on the Vulcan circuit."

What's the difference between an effect with a tone-stack and a preamp, please?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 11, 2018, 01:53:11 PM
The vulcan circuit is a preamp. Basically every effect is a preamp, considering it amplifies and shapes the signal. There is no difference strictly speaking. That being said, most people are used to the standard gain stage + TMB tone stack, since this FMV configuration cuts mids usually at 400 or 800 Hz, and that sounds pleasing to the ears.

Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 11, 2018, 02:28:23 PM
Thanks everyone.

Guess what? I have another question if I may  ::) Can I add another tone stack bypassing a few gain stages to have two separate channels for clean / drive? Something like this

(http://i67.tinypic.com/2qscn46.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on January 12, 2018, 07:19:34 AM
yes I guess any low signal circuit could be termed a preamp but a lot of them
will colour the sound in a negative way and because it's hard wired into the Amp you are stuck with one sound only.
I'm yet to meet a guitar player who is happy with all 2/3 channels of his Amp.  :lmao:

What you need is a 2 or 3 stage preamp the first matching the guitar with some gain and the second stage runs a tone control.
If the tone is passive then you have to adjust the gain to pull up the signal loss in stage 2.

This can be done with one dual opamp running single or dual supply.
Those fancy circuits with a whole pile of parts is just going to be a nightmare for the novice. (hint)
BTW, I have tested that vulcan circuit and it's not that great,, as a pedal effect it may help but there are likely better (easier) ways for simulating the valve sound.

Be aware of sound clips as they can be misleading,, a lot of demos are just $20 distortion circuits (that have been around for years) plugged into Valve amplifiers that most of us can't afford to even look at. They hit the pedal and your hear a sound to die for. <3) <3) <3)

So you go buy that pedal and plug into a small budget bedroom SS amp and it
sounds nothing like the demo,, most will feel ripped off. :grr :grr :grr

Reality;
Almost any crap dirt pedal will sound stunning through a big monster Valve Amp,, But not quite so easy to do with all SS rigs,, though some Can do that trick.

Reason;
With any half decent Valve amp you only have to send it a bigger signal from any old dirt pedal and the Valves do the magic because of the way they work.
(A whole other subject that has filled many books)

This magic trick will never happen with a small simple design bedroom SS Amp combo with a 6 inch speaker. :'( :'( :'(

So with All SS circuitry you need to do a lot of fancy circuit tricks to get same or similar outcomes. A SS power stage is very different to a Valve power stage and most SS Pwr
stages won't compress like a Valve rig so you have to do most of the tricks in the pre stages.

MY advice is build a basic preamp, a single clean channel is good because you have a basic clean sound which is not too coloured. You then try out different pedal circuits which work with your Amp.

I have a simple Casino bedroom Amp here (read Cheap) and with a few tweaks it
actually sounds ok through a small speaker but much better through my quad box. :dbtu:

The added dirt circuit is not brilliant but the clean is good.
I've tweaked the tone shaping to wipe off the excess hi freq that these small amps produce which gives a much smoother sound but don't be fooled there is more treble than you will ever need ,,unless you have tin ears.

hope it helps,, Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on January 12, 2018, 07:54:38 AM
Just found some old pics of the Casino might give you some ideas to work with.
It came to me free with a dead power chip,, I had a few spares so I messed around until I got it to sound much better.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 13, 2018, 05:35:10 AM
I'll do as you say: single channel it is.
I think I have more than enough things to try by now, one thing at a time to see how everything affects the tone.

Thanks a lot for the schematics too, Phil
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 28, 2018, 03:45:54 PM
First hurdle in my build: the TDA7297 is bridged so the outputs aren't grounded. I'm building the amp in a cannibalized computer PSU chassis, so the speaker OUT sockets look like these: (https://ae01.alicdn.com/kf/HTB1pBwLLFXXXXbsaXXXq6xXFXXXS/3pcs-6-35mm-1-4-Mono-Chassis-Socket-Jack-connector.jpg)

Of course those sockets ground the speakers when mounted on a metal chassis like mine. I think I'm lucky I didn't blow up the chip, ugh!

ANy ideas on how to isolate the speakers connections please?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: blackcorvo on January 28, 2018, 08:02:29 PM
If you don't mind waiting, there are isolation washers you could try using for this:

https://www.tubedepot.com/products/isolation-washers-for-1-4-input-jack-flat-shoulder

If you'd rather not wait, or youc can't get that kind of washer, you could cut out a square in the chassis and use a plastic panel to mount the speaker-out jack to it. Or maybe a wooden panel, whatever fits the style of your build better.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 29, 2018, 05:27:53 AM
If you don't mind waiting, there are isolation washers you could try using for this:

https://www.tubedepot.com/products/isolation-washers-for-1-4-input-jack-flat-shoulder

If you'd rather not wait, or youc can't get that kind of washer, you could cut out a square in the chassis and use a plastic panel to mount the speaker-out jack to it. Or maybe a wooden panel, whatever fits the style of your build better.

Thank you, great stuff. Those washers look exactly like what I need. Problem is I'm in Europe and the $14 shipping fee is too much for such an inexpensive item, I'll see if I can find those somewhere else. If I can't I'll probably use a wooden panel

ETA: I think these connectors might work

(https://ae01.alicdn.com/kf/HTB1yDkOXN6I8KJjSszfq6yZVXXat/5-pcs-Screw-0-25-1-4-6-35-mm-Microphone-Jack-Socket-6-Contact-3.jpg_640x640.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 29, 2018, 06:02:10 AM
Yes, just buy those plastic jacks, they are way more reliable anyway, IMHO.
Check out musikding, they have low shipping rates for small orders.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: blackcorvo on January 29, 2018, 09:06:21 AM
I agree with Katoda, the plastic jacks are pretty good!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 29, 2018, 09:12:25 AM
Thanks guys. They're dirt cheap too! Just ordered a bunch of them off of ebay for a couple €.

I already have the TDA7297 power amp installed and the component layout pretty much done. Driven by my Buzz Fuss pedal it's already usable (and quite loud but of course no tonestack) so I can have some fun playing while the preamp parts arrive in the mail.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 29, 2018, 09:43:13 AM
I have loads of hum and noise from the power supply though, a 12V 1.5A unit that came with an external hard drive

Time to check this out I guess: Topic: Grounding techniques (https://www.ssguitar.com/index.php?topic=288.0)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: blackcorvo on January 29, 2018, 11:11:35 AM
I have loads of hum and noise from the power supply though, a 12V 1.5A unit that came with an external hard drive

Time to check this out I guess: Topic: Grounding techniques (https://www.ssguitar.com/index.php?topic=288.0)

Perhaps if we see some pics of your build so far, we might see what's wrong. Also, measure the voltage of the power supply when you have the amp running, maybe the amp is loading the supply down.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 29, 2018, 11:52:45 AM
I have loads of hum and noise from the power supply though, a 12V 1.5A unit that came with an external hard drive

Time to check this out I guess: Topic: Grounding techniques (https://www.ssguitar.com/index.php?topic=288.0)

Perhaps if we see some pics of your build so far, we might see what's wrong. Also, measure the voltage of the power supply when you have the amp running, maybe the amp is loading the supply down.

With the Bazz Fuzz at maximum gain and volume and the power amp maxed out too I measured 12.1V, basically the same as unloaded.

Here are a couple of pics:

(http://i64.tinypic.com/x5drvt.jpg)

(http://i67.tinypic.com/14ipjf8.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 29, 2018, 11:57:23 AM
I should probably go with shielded wire for the input right? Right now I'm using unshielded 22 AWG with silicon insulation
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 04:06:39 AM
Yes, definitely use shielded wire. If you're a cheap scavenger like me you can reuse some old usb cables, they have good shielding and 4 cores.

Since you are using a hard drive (probably switching) power supply, you need to filter the hell out of it, using big electrolytics paralleled to small ceramics, maybe even throw a choke in ( you have some of these if you raided the computer PSU ). Otherwise there will be noise in the circuit. Perhaps you could even add in a small LDO voltage regulator for the preamp circuit to minimize the noise.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 04:33:25 AM
Yes, definitely use shielded wire. If you're a cheap scavenger like me you can reuse some old usb cables, they have good shielding and 4 cores.

Since you are using a hard drive (probably switching) power supply, you need to filter the hell out of it, using big electrolytics paralleled to small ceramics, maybe even throw a choke in ( you have some of these if you raided the computer PSU ). Otherwise there will be noise in the circuit. Perhaps you could even add in a small LDO voltage regulator for the preamp circuit to minimize the noise.

Cheap scavenger here too haha! That's exactly what this project is all about: reuse as much and learn as much as I can. thanks for those great suggestions. I ripped an RCA cable for some shielded wire, not sure how good the shielding is on this one but it didn't help too much. May I ask why would a 4 core cable be a better option than a single core one? I wired mine using the shield as ground and the core as hot. For what I could gather in my interwebz research that's how it's supposed to be done. Is that right?

Here's what's left of the PSU board, time to figure out how to build a filter for the power supply (I don't even know what a choke is LOL)

(http://i66.tinypic.com/nq8uae.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 05:54:17 AM
I've tried 1000uF, 100uF and .1uF between 12V and ground with no perceivable results  ???
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 06:50:16 AM
I didn't mean that it is better (or more usable for that matter) to have 4 conductor shielded cable, I just wanted to say what to expect. You can, however, use two or more of the conductors for the pots in the same signal path, like on a volume/gain pot - one pin is ground, and the other two can be soldered to different wires inside the cable. It just saves some space and results in a cleaner looking build, but the downside is that there is a lot of tension on the individual cores (if the plastic insulation is too thick), which might result in breaking wires.

Your cable wiring is correct, the shield is ground and the centre is the signal. You must watch for ground loops here, make sure that there aren't multiple connections to different grounds from any single point.

A choke is an inductor, a coil of wire wrapped around a magnetic material (ferrite, in this case). If the switching noise is really the problem, then try googling LC low pass filter. Because you dont know the coils inductance, it might be a hit or miss, but taking that toroidal psu coil and soldering some leads together, so it has all the wraps around the core in series and in the same direction, and then placing it in front of your amps power supply (so that it is followed by paralleled 1000uF and 100nF caps) might help a bit.

Keep the input of the power supply short and away from the preamp, as the switching from the external unit might be creating some quite strong EMI.

EDIT: The -3dB cutoff frequency of an LC filter is given as
f=1/(2*pi*sqrt(L*C))
So if the switching frequency is the same as the LC cutoff frequency, the power supply ripple will be 3dB smaller. Now, electrolytics have higher ESR and ESR, so for effective high frequency decoupling you want ceramics. A lot of them in parallel. Measure the coils inductance if you can, and then try to make the cutoff frequency a couple of times lower than the switching frequency.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 07:28:09 AM
I didn't mean that it is better (or more usable for that matter) to have 4 conductor shielded cable, I just wanted to say what to expect. You can, however, use two or more of the conductors for the pots in the same signal path, like on a volume/gain pot - one pin is ground, and the other two can be soldered to different wires inside the cable. It just saves some space and results in a cleaner looking build, but the downside is that there is a lot of tension on the individual cores (if the plastic insulation is too thick), which might result in breaking wires.

Your cable wiring is correct, the shield is ground and the centre is the signal. You must watch for ground loops here, make sure that there aren't multiple connections to different grounds from any single point.

A choke is an inductor, a coil of wire wrapped around a magnetic material (ferrite, in this case). If the switching noise is really the problem, then try googling LC low pass filter. Because you dont know the coils inductance, it might be a hit or miss, but taking that toroidal psu coil and soldering some leads together, so it has all the wraps around the core in series and in the same direction, and then placing it in front of your amps power supply (so that it is followed by paralleled 1000uF and 100nF caps) might help a bit.

Keep the input of the power supply short and away from the preamp, as the switching from the external unit might be creating some quite strong EMI.

Awesome, thanks so much Katoda. I own one of these meters (https://www.ebay.com/itm/LCR-T4-ESR-Meter-Transistor-Tester-Diode-Triode-Capacitance-SCR-Inductance-New/112527481729?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649) so I can measure the coils' inductance.

I still have no preamp in there, I'm using the Bazz Fuss pedal for the time being, but I'll move the supply input to the other side. I already have a hole in the chassis right where the power amp supply voltage input sits. Although I was planning to feed 12V to the preamp too instead of 9V for "máximum" gain so I'll need a wire from the 12V input to the preamp anyway...
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 07:45:30 AM
EDIT: The -3dB cutoff frequency of an LC filter is given as
f=1/(2*pi*sqrt(L*C))
So if the switching frequency is the same as the LC cutoff frequency, the power supply ripple will be 3dB smaller. Now, electrolytics have higher ESR and ESR, so for effective high frequency decoupling you want ceramics. A lot of them in parallel. Measure the coils inductance if you can, and then try to make the cutoff frequency a couple of times lower than the switching frequency.

I see what you mean now. I need a large enough inductor or else I'd need a crap load of caps. I have a tiny 0.05mH coil here that won't cut it cause I'd need 5000uF in caps to cut at some 100Hz if my numbers are right. I'll try the larger coil with all the leads in series as you suggested
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 09:01:09 AM
No problemat all, we're all here to learn :)

If the hum is mainly 100Hz-ish, the smps switching noise might not be the problem after all, since they operate at higher frequencies. If you get the power from a switcher, the ground is probably not connected to the "earth" connector of the mains. That would mean that you could be picking up mains noise from everywhere around you. Does the amount of noise reduce if you touch the ground with your finger? If it does, there's your problem. If not, the input might still be picking something from the mains, if it is not completely encased in grounded metal.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 09:09:11 AM
No problemat all, we're all here to learn :)

If the hum is mainly 100Hz-ish, the smps switching noise might not be the problem after all, since they operate at higher frequencies. If you get the power from a switcher, the ground is probably not connected to the "earth" connector of the mains. That would mean that you could be picking up mains noise from everywhere around you. Does the amount of noise reduce if you touch the ground with your finger? If it does, there's your problem. If not, the input might still be picking something from the mains, if it is not completely encased in grounded metal.

Yeah, it goes away when I touch the strings for the most part. The power supply is definitely not connected to main's ground. I guess it's time to look up a proper power supply?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 09:37:59 AM
Awesome, now that you know the source of the hum, you can take measures to eliminate it. It might be as simple as opening the hard drive PSU and connecting the chassis to the output ground, or as annoying as having to buy/build another PSU, if the current doesn't even have a 3-pronged mains cable.

If you are feeling adventurous, you could open the hard drive PSU, desolder the current 2-prong cable and replace it with a 3-pronged one, connecting the mains earth to the output ground (be careful if you do that, small mistake could mean a large fire and/or electrocution!!!)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 10:02:54 AM
Awesome, now that you know the source of the hum, you can take measures to eliminate it. It might be as simple as opening the hard drive PSU and connecting the chassis to the output ground, or as annoying as having to buy/build another PSU, if the current doesn't even have a 3-pronged mains cable.

If you are feeling adventurous, you could open the hard drive PSU, desolder the current 2-prong cable and replace it with a 3-pronged one, connecting the mains earth to the output ground (be careful if you do that, small mistake could mean a large fire and/or electrocution!!!)

Unfortunately it's one of those without a prong: the plug is integrated in the whole thing like this one:

(https://images-na.ssl-images-amazon.com/images/I/91DgYfkN8fL._SX522_.jpg)

What if I take it apart and mount the inner circuit inside my chassis with a mains ground connection? let's see what's inside....
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 10:41:31 AM
Just to be clear, the mains earth should be connected to the power supply's negative DC output, right? I mean the sleeve of the DC jack
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 10:55:15 AM
Crap, i was hoping there would be a cable... I wouldn't recommend mounting it inside the chassis, the coils would probably radiate too much for such a small enclosure. If the smps circuit has a transformer (as in - not just an inductor), you could fit in in another enclosure, one that would provide a connection to earth, but that's quite an advanced challenge, because you're dealing with potentially lethal voltages there.
If it's just a buck converter, there's nothing you can do but to buy another PSU. No mains isolation is a no-no.

Yes, the earth should be connected to the negative terminal, the ground.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 02:31:05 PM
Crap, i was hoping there would be a cable... I wouldn't recommend mounting it inside the chassis, the coils would probably radiate too much for such a small enclosure. If the smps circuit has a transformer (as in - not just an inductor), you could fit in in another enclosure, one that would provide a connection to earth, but that's quite an advanced challenge, because you're dealing with potentially lethal voltages there.
If it's just a buck converter, there's nothing you can do but to buy another PSU. No mains isolation is a no-no.

Yes, the earth should be connected to the negative terminal, the ground.

Umm, not sure if what I did is safe then:

(http://i66.tinypic.com/f389k5.jpg)

So I ripped the power supply, wired the hole thing with one lead from DC(-) to ground, wrapped the PSU in duct tape and mounted it like that. It works great but is that thing safe?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 03:37:46 PM
 :lmao: I wasn't expecting that at all  :)
If everything is securely in place and it won't move, then I guess it's OK. If the brown empty pcb is intented for the preamp, then you might have some mains hum when it gets amplified through it. Keep the input signal as far away as possible from that psu.
+1 for creativity  :)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 04:51:50 PM
Oh, and here's a pic of the SMPS. Looks like it has a transformer indeed

(http://i67.tinypic.com/23mrlgo.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on January 30, 2018, 05:09:13 PM
:lmao: I wasn't expecting that at all  :)
If everything is securely in place and it won't move, then I guess it's OK. If the brown empty pcb is intented for the preamp, then you might have some mains hum when it gets amplified through it. Keep the input signal as far away as possible from that psu.
+1 for creativity  :)

Yes, that's where the preamp will go. I'll move the input jack farther away from the PSU and the PCB input will sit right underneath it, so the wire will be a few millimeter long, like 12 mm or so. Hope that works just fine. I guess I should have mounted the PSU with the mains facing the opposite side. Will fix that. Man, I appreciate your input, really do, Thank you!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: Katoda on January 30, 2018, 05:15:18 PM
:lmao: I wasn't expecting that at all  :)
If everything is securely in place and it won't move, then I guess it's OK. If the brown empty pcb is intented for the preamp, then you might have some mains hum when it gets amplified through it. Keep the input signal as far away as possible from that psu.
+1 for creativity  :)

Yes, that's where the preamp will go. I'll move the input jack farther away from the PSU and the PCB input will sit right underneath it, so the wire will be a few millimeter long, like 12 mm or so. Hope that works just fine. I guess I should have mounted the PSU with the mains facing the opposite side. Will fix that. Man, I appreciate your input, really do, Thank you!

No problem at all. Good luck with your build then  :dbtu:
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 11, 2018, 07:04:09 PM
yes I guess any low signal circuit could be termed a preamp but a lot of them
will colour the sound in a negative way and because it's hard wired into the Amp you are stuck with one sound only.
I'm yet to meet a guitar player who is happy with all 2/3 channels of his Amp.  :lmao:

What you need is a 2 or 3 stage preamp the first matching the guitar with some gain and the second stage runs a tone control.
If the tone is passive then you have to adjust the gain to pull up the signal loss in stage 2.

This can be done with one dual opamp running single or dual supply.
Those fancy circuits with a whole pile of parts is just going to be a nightmare for the novice. (hint)
BTW, I have tested that vulcan circuit and it's not that great,, as a pedal effect it may help but there are likely better (easier) ways for simulating the valve sound.

Be aware of sound clips as they can be misleading,, a lot of demos are just $20 distortion circuits (that have been around for years) plugged into Valve amplifiers that most of us can't afford to even look at. They hit the pedal and your hear a sound to die for. <3) <3) <3)

So you go buy that pedal and plug into a small budget bedroom SS amp and it
sounds nothing like the demo,, most will feel ripped off. :grr :grr :grr

Reality;
Almost any crap dirt pedal will sound stunning through a big monster Valve Amp,, But not quite so easy to do with all SS rigs,, though some Can do that trick.

Reason;
With any half decent Valve amp you only have to send it a bigger signal from any old dirt pedal and the Valves do the magic because of the way they work.
(A whole other subject that has filled many books)

This magic trick will never happen with a small simple design bedroom SS Amp combo with a 6 inch speaker. :'( :'( :'(

So with All SS circuitry you need to do a lot of fancy circuit tricks to get same or similar outcomes. A SS power stage is very different to a Valve power stage and most SS Pwr
stages won't compress like a Valve rig so you have to do most of the tricks in the pre stages.

MY advice is build a basic preamp, a single clean channel is good because you have a basic clean sound which is not too coloured. You then try out different pedal circuits which work with your Amp.

I have a simple Casino bedroom Amp here (read Cheap) and with a few tweaks it
actually sounds ok through a small speaker but much better through my quad box. :dbtu:

The added dirt circuit is not brilliant but the clean is good.
I've tweaked the tone shaping to wipe off the excess hi freq that these small amps produce which gives a much smoother sound but don't be fooled there is more treble than you will ever need ,,unless you have tin ears.

hope it helps,, Phil.

Phil, if you read this, can you please let me know which chips are those in your Casino 12? I searched the forums to no avail

I ordered LM386 & TL082's a couple of weeks ago, will any of those do?

EDIT: I just reread your post and you mentioned that any dual opamp would do, so I'm guessing the TL082 is fine?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 12, 2018, 06:21:53 AM
Yes any of the usual opamps will do the same job give or take an electron 8) but TL07X is likely a better chip than lm4558.

The TL082 has low current draw which might be good for battery powered circuits but that is not needed in a wall powered unit.
But yes use those if you wish.

The LM833 is aimed at audio and is a top shelf chip. :tu:
I doubt you will note much difference in performance with any of the usual chips.
Heck it's a guitar amp so the last thing you want is 20/20 bandwidth.
 
The LM386 is powerchip and not really much use in the preamp unless you want it for some special booster. I can't remember the name but a couple of pedals use those to get big distortion sounds.
Others here may recall those circuits??
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 12, 2018, 08:12:07 AM
Yes any of the usual opamps will do the same job give or take an electron 8) but TL07X is likely a better chip than lm4558.

The TL082 has low current draw which might be good for battery powered circuits but that is not needed in a wall powered unit.
But yes use those if you wish.

The LM833 is aimed at audio and is a top shelf chip. :tu:
I doubt you will note much difference in performance with any of the usual chips.
Heck it's a guitar amp so the last thing you want is 20/20 bandwidth.
 
The LM386 is powerchip and not really much use in the preamp unless you want it for some special booster. I can't remember the name but a couple of pedals use those to get big distortion sounds.
Others here may recall those circuits??
Phil.

Thanks Phil. I've retaken the project this weekend and been doing some reading about JFET preamps, just because I have some of those, but it looks like JFETS either don't provide enough gain to drive a preamp with a full tone stack or if they do, they clip too easily (J201) to get a clean channel as you suggested, so I'm going with your Casino 12 (just the clean channel for now). I don't have trim pots to bias those JFETS anyway and for what I could gather they tend to be all over the place in terms of their electrical properties so I can't just go by an schematic and expect it to work right off the bat.

Is this the correct schematic for your Casino 12, clean channel only, please? (see attachment)

Moar questions!!!11!!11one!

I take it I can use 12V with those TL082?

What's the gain of that Casino 12 clean channel?

And finally, I have it wired so that the preamp output is fed to both channels of the power amp even though I'll only be using one speaker most of the times. This is a bad idea, isn't it? That will halve the power amp input impedance (from 30K Ohms to 15K Ohms) and according to Duncan's tone stack calculator, will attenuate the signal another 6dB (shouldn't it be 3dB?). So if that's correct, does it even make any sense to add a switch to connect the second channel to use a second speaker, considering that doubling the power output (+3dB) and doubling the cone area (another 3dB) will simply cancel out the 6dB loss from the input impedance halving? I don't think my 12V 1.5A wall wart power supply can cope with both channels anyway (some 6W per channel at 12V according to the TDA7297 datasheet)

Maybe I can use that second channel for a switchable  headphone jack output by connecting 50 - 100 Ohms / 2W resistor in series to attenuate the signal enough?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 12, 2018, 07:44:55 PM

Re the clean channel, Yes everything in green box is correct.

Oh I just realized that you obviously have a single 12 volt supply,, in which case you will need to alter the Casino circuit as it assumes split supply.
You will need a bias voltage, look at pedal circuits for clues.
If you can't work it out I'll redraw the schematic for single supply.

Re the 2nd half of the power chip,, just leave the pins open as it will just idle with no load and not draw much power from the supply.
with some chips you can just ground the input to be sure nothing weird happens.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 12, 2018, 08:03:43 PM

Re the clean channel, Yes everything in green box is correct.

Oh I just realized that you obviously have a single 12 volt supply,, in which case you will need to alter the Casino circuit as it assumes split supply.
You will need a bias voltage, look at pedal circuits for clues.
If you can't work it out I'll redraw the schematic for single supply.

Re the 2nd half of the power chip,, just leave the pins open as it will just idle with no load and not draw much power from the supply.
with some chips you can just ground the input to be sure nothing weird happens.
Phil.

Re: bias voltage, I guess that would be a voltage divider to get +6V, GND, -6V? Perhaps with large resistors to minimize current through the divider?

12V ----|----------------------  +6V
            /
            / 10K Ohms
            /
            ----------------------- GND
            /
            / 10K Ohms
            /
0V------|----------------------  -6V
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 12, 2018, 09:53:33 PM
The divider above would mess up the power amp ground, right? Perhaps this is more like it?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 12, 2018, 11:43:12 PM
Not quite right, so it becomes this.


12V ----|---------------------- +12V
            /
            / 10K Ohms
            /
            ----------------------- +6V Bias voltage
            /
            / 10K Ohms
            /
0V------|----------------------  Ground/Common

This is where you can resort to a simple rule of thumb; which is the  1k per volt rule.
So to get a bias voltage with a 12volt supply you need at least 2x 6k resistors so 10k x10k is fine and won't load down the supply,,in fact you can go larger even up to 100k as it makes little difference.
All you want is a reference voltage so the opamp can work at that offset, a vitual ground (the bias voltage).

So R2 500k now goes to bias voltage not ground.
Just look at the many dirt pedal circuits on the net and you will see how that is done. :tu:

I'm busy right now but I'll try to redraw it up in the next day or so.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 14, 2018, 01:15:02 AM
Here you go Dazz, :tu:
Try this out, it should work and deliver plenty of signal to the power amp section.

If you breadboard this first then you can tweak some of the values to taste. 8)
Cheers, Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 14, 2018, 08:40:47 AM
Here you go Dazz, :tu:
Try this out, it should work and deliver plenty of signal to the power amp section.

If you breadboard this first then you can tweak some of the values to taste. 8)
Cheers, Phil.

Thank you Phil, much appreciated.
Can't wait for the parts to arrive!
Is R2's 470K the input impedance?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 14, 2018, 09:51:58 PM
R2 can be anywhere from 220k up to 1Meg.
The input Z will always be a lower number than the value of R2,, but not much.
The higher Z you go the more sensitive the input but high Z can be problematic if you have lots of hi gain pedals.

Try a few values and see/hear for yourself,, most will pick 1Meg because you get a bit more perceived volume but at the expense of early distortion in the power amp.
As your power chip is small and only running 12 volts then there is not much headroom.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 17, 2018, 05:17:06 PM
I got some TDA7267A's in the mail yesterday (the chip I initially planned to use) so I thought I would do something with them and take the opportunity to practice with a little 1W amp. I used an MPF102 JFET for the preamp (Feltzer valve), in preparation for the drive stage of the larger project but I don't like too much the way it sounds overdriven. Probably to be expected considering I'm using some cheap 3'' speakers.

There's something I don't understand about this little amp: it works like a charm on a 9V or 12V wall wart, but when powered by a 9V battery it sounds like crap, and I get these weird oscillations that sound like heli rotors. I measured 150mA at the battery, doesn't sound like too much of a current draw to choke the battery does it?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 19, 2018, 08:19:11 AM
Maybe add a 10~47uF cap on the supply.
With such a small case you have to watch out for inductive coupling which can cause all sorts of problems.
Also if the battery is old that might cause problems.
Better minds here may know more.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 19, 2018, 08:57:22 AM
Maybe add a 10~47uF cap on the supply.
With such a small case you have to watch out for inductive coupling which can cause all sorts of problems.
Also if the battery is old that might cause problems.
Better minds here may know more.
Phil.

Thanks Phil. I already have a 100uF cap at the supply, per TDA7267A schematics. Pretty sure the battery is at fault, it's fresh but a cheap one. Measures 9.5V unplugged, goes down to 8.8V as soon as I connect it to the amp, and down to 7.7V when I strum a chord at full volume.

Well, sorry to be such a pest but I have yet another question about the larger amp (Casino 12 + TDA7297). I bought me a power supply, one of those universal laptop chargers that runs at anything between 12 and 24V which seems to work really well and dead silent after grounding the DC negative output.
I don't think I want anything over 15V through the TDA7297 since that's when it reaches 10W and it starts to distort (according to the datasheet), but let's say I add a DC input jack so that I can run the amp off the internal 12V psu or this external supply: that would put 15V (or more) at the output of the disconnected internal 12V supply. Can this damage the 12V supply? Also, what's the maximum Vdd I can feed your Casino 12 please?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 19, 2018, 11:03:46 PM


I don't think I want anything over 15V through the TDA7297 since that's when it reaches 10W and it starts to distort (according to the datasheet),

whatever the max supply voltage reads on the data sheet,, don't go above that.

but let's say I add a DC input jack so that I can run the amp off the internal 12V psu or this external supply: that would put 15V (or more) at the output of the disconnected internal 12V supply. Can this damage the 12V supply?

Sorry but without a drawing there is little to go on.
If the internal suppy is *Disconnected* then I assume there is no problem powering from an external supply.
Most pedals have a switch built into the DC socket so when you insert an external wall wart the battery is disconnected.

Also, what's the maximum Vdd I can feed your Casino 12 please?

Whatever the data sheet reads for the chips you are using.
Most will run on 30VDC or 15-0-15VDC.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 20, 2018, 03:58:18 AM
Yeah, I should have figured those out myself, sorry about the dumb questions.
I knew in the back of my mind that 3rd lug in the DC socket was there for a reason *blush*
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 20, 2018, 06:04:11 AM
I'm afraid I have another question (hopefully this one is not as dumb as the previous ones). I don't have many 10K resistors right now so I'll be using something higher for the bias resistors. I understand R7, R17 and R18 are bias resistors, but what about R14 in the 3rd opamp? There was a 10K resistor there in the original schematics so I'm not sure if that needs to be matched to the value of R7, R17 and R18
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on February 20, 2018, 07:40:03 AM
As long as R17 and R18 are the same value it will still give you half voltage at the bias node. R2, R7, and R12 give each input a ground reference to work from so the signal can swing evenly pos and neg of the bias point.
(opamp basics, the positive input always needs a DC path to reference, in this case it's the half voltage bias node)

R7 can be a bit higher or lower than 10k,, lower values may pull down the gain, too high and it may effect the filter network in front of it.
R12 needs to be as big as possible, lower values there will effect how well the tone controls work. Try 2meg if you want.

R14 along with R13 effects the gain of U3, higher values at R14 will lower the gain while higher values of R13 will increase the gain.
R15 and C16 pull a bit more treble from that stage.

If you use a bread board to test you can tweak the values till you find the best outcome for you needs. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on February 20, 2018, 08:30:30 AM
Thank you for the detailed explanation and your patience too, Phil  :cheesy:
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 01, 2018, 01:13:08 PM
The parts finally arrived and I'm already prototyping the first stage of the preamp on the breadboard.
And of course I have more questions  :-[

I've been reading about caps and how ceramics are not the best for audio since their non linear, but the smallest film cap I have is 330pF. There's a bunch of 50pF in the circuit, can I use ceramics for those or should I shop for smaller film caps?

Also, the 1uF electrolytics I have measure about 5% ESR. For what I could gather this is normal for 50V 1uF, but what if I parallel two 47nF to half the ESR? is there any benefit to that?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 01, 2018, 01:59:52 PM
Well, I get no sound from the first stage straight to the speaker. I've double checked the wiring and it seems to be OK

(see attachment)

EDIT: nevermind! I run it through that tin can amp I built and it's definitely working and amplifying! woohoo!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 01, 2018, 02:35:47 PM
R2 can be anywhere from 220k up to 1Meg.
The input Z will always be a lower number than the value of R2,, but not much.
The higher Z you go the more sensitive the input but high Z can be problematic if you have lots of hi gain pedals.

Try a few values and see/hear for yourself,, most will pick 1Meg because you get a bit more perceived volume but at the expense of early distortion in the power amp.
As your power chip is small and only running 12 volts then there is not much headroom.
Phil.

Something just occurred to me. What if I swap R2 by a 1M pot and use that as a volume instead of the 10K VR4 as in the attachment circuit? That way I can control the level of the signal at the preamp output to avoid clipping there, right? I plan on adding an overdrive stage before your Casino preamp, probably some JFET based pedal, with a switch to bypass it for pure clean sound
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 02, 2018, 03:48:32 AM
Hi Dazz,,Yes you could do that but when the OD circuit is bypassed that 1 meg pot becomes passive, much like the volume pot on your guitar and I'm not sure if that is a good idea but try it out first before you commit to a build. :-X

Normally an effects pedal has (or should have) a level pot to control the output level to control the output strength.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 02, 2018, 07:23:13 AM
Hi Dazz,,Yes you could do that but when the OD circuit is bypassed that 1 meg pot becomes passive, much like the volume pot on your guitar and I'm not sure if that is a good idea but try it out first before you commit to a build. :-X

Normally an effects pedal has (or should have) a level pot to control the output level to control the output strength.
Phil.

Sorry, I said the idea is to "control the level of the signal at the preamp output" when I meant at the preamp input, obviously. But anyway, what do you mean by "that 1 meg pot becomes passive" please? Wouldn't it simply act like a variable input sensitivity or input impedance at the Casino preamp? I'll try it and see how that goes. The thing is that I'd like to keep volume and gain pots to a minimum but also have that preamp input signal control working both when the OD circuit is switched on and off, so I can have the best of both worlds: maximize sensitivity (and volume) or lower it for hotter/active pickups
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 02, 2018, 07:55:00 AM
All good,,,Yes I figured you meant preamp Input. ;)

No because when the OD circuit is disconnected you would have to readjust the 1 meg pot to maintain levels, I doubt that would be user friendly. :-X
Why passive?
Because if you draw a schematic of the guitar (passive volume) and the preamp input you will see that you then have 2 passive pots in the signal path. So as you need a level control on the output of the OD anyway,, add it there where it would be of more use.

Anything in front of the First Active element of an amplifier is effectively a passive component, So in a normal Electric guitar all the PU's and pots are passive as there is no amplification.
If you have Active PU's then that changes things a bit.
You might need to have 2 inputs like professional rigs have.
others here may have better options but in my Experience,,, I hate Active PU's :grr
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 02, 2018, 08:21:52 AM
All good,,,Yes I figured you meant preamp Input. ;)

No because when the OD circuit is disconnected you would have to readjust the 1 meg pot to maintain levels, I doubt that would be user friendly. :-X
Why passive?
Because if you draw a schematic of the guitar (passive volume) and the preamp input you will see that you then have 2 passive pots in the signal path. So as you need a level control on the output of the OD anyway,, add it there where it would be of more use.

Anything in front of the First Active element of an amplifier is effectively a passive component, So in a normal Electric guitar all the PU's and pots are passive as there is no amplification.
If you have Active PU's then that changes things a bit.
You might need to have 2 inputs like professional rigs have.
others here may have better options but in my Experience,,, I hate Active PU's :grr
Phil.

Understood, thanks so much Phil. No, I don't own any guitars with active pups, it's just that that previous post of yours got me thinking about input impedance because I'd like to maximize the amp's output but also avoid clipping at the preamp. I have a strat with fat 50's style pups that are quite hot, so I'll use that as a reference and pick the highest R2 so that the amp still stays clean. I guess I'm overthinking it a bit since for what I know half the input impedance / wattage is just 3dB quieter. At most I might put a switchable resistor in parallel with R2 for low/high impedance

So yeah, that settles it then: no low input impedance input and no volume pot at the preamp input.  :tu:
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 02, 2018, 07:45:26 PM
All good,,,Yes I figured you meant preamp Input. ;)

No because when the OD circuit is disconnected you would have to readjust the 1 meg pot to maintain levels, I doubt that would be user friendly. :-X
Why passive?
Because if you draw a schematic of the guitar (passive volume) and the preamp input you will see that you then have 2 passive pots in the signal path. So as you need a level control on the output of the OD anyway,, add it there where it would be of more use.

Anything in front of the First Active element of an amplifier is effectively a passive component, So in a normal Electric guitar all the PU's and pots are passive as there is no amplification.
If you have Active PU's then that changes things a bit.
You might need to have 2 inputs like professional rigs have.
others here may have better options but in my Experience,,, I hate Active PU's :grr
Phil.

Phil, by how much would you calculate R2 could be increased from 470K if I fed the amp say 15V instead of 12V?
Also, I'm gonna try a few OD's, one of the candidates is this JFET Professor Tweed (http://www.runoffgroove.com/professor.html). I take it will color the sound somewhat even if the gain is low enough as to not clip it's output nor the preamp's? because if it doesn't I guess I could do without the OD bypass switch
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 03, 2018, 01:55:24 PM
Phil, what's the taper of the volume pot please? I take it log/audio, right? I think I know the tone stack's: 250K's are logarithmic and the 10K is linear, correct?
Also, can I use a different value for the volume pot or is the 10K critical?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 03, 2018, 09:20:58 PM
Opamps were designed to work within a window of psu voltages,, sometimes mentioned on data sheets. That is why they can be used in pedals (9Volts or less) and up to 30Volts or more. Some chips are designed to work down to 3 or 4 volts. (TL062 is one such chip) So 12 or 15 volts makes no difference, just use what value works for you.
Anywhere from 220k up to 1 meg, the higher the value the more sensitive the input.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 03, 2018, 09:23:35 PM
Phil, what's the taper of the volume pot please? I take it log/audio, right? I think I know the tone stack's: 250K's are logarithmic and the 10K is linear, correct?
Also, can I use a different value for the volume pot or is the 10K critical?

Yes not over critical but Audio taper is likely better.
Re Tone; Treble can be linear,, bass Log,, mid linear.

output volume; not critical,,, up to 100k if you want.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 04, 2018, 06:49:26 AM
Phil, what's the taper of the volume pot please? I take it log/audio, right? I think I know the tone stack's: 250K's are logarithmic and the 10K is linear, correct?
Also, can I use a different value for the volume pot or is the 10K critical?

Yes not over critical but Audio taper is likely better.
Re Tone; Treble can be linear,, bass Log,, mid linear.

output volume; not critical,,, up to 100k if you want.
Phil.

Got it, thanks.
Well, it's almost ready, if I don't manage to screw up wiring the last opamp I should have it ready to rock today. My prototyping sucks though, the thing is a mess, hahaha. I've done some reading on perf-boards and learned that parasitic capacitance can cause some issues in audio circuits (cut higher frequencies). We'll see how it sounds, hopefully in a few hours (fingers crossed)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 04, 2018, 04:01:58 PM
OK, it's finished and it works. Well, sort of. The tonestack is all messed up and I don't get much output at all.
Are these pot lugs actually supposed to be disconnected? (see attachment)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 05, 2018, 07:39:41 AM
I assume you have power to u3?  I did not draw everything as power and ground are often left out for clarity.
If using 2 dual opamps then you have to power the other opamp.

Tone pots are correct you can bridge top and middle of bass and mid if you wish.
Treble is a voltage divider while bass and mid are wired as a variable resistor.

Quick check with a meter on power pins and also check the 3 positive inputs,, they should read close to half voltage,, your bias voltage.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 05, 2018, 08:56:46 AM
I assume you have power to u3?  I did not draw everything as power and ground are often left out for clarity.
If using 2 dual opamps then you have to power the other opamp.

Tone pots are correct you can bridge top and middle of bass and mid if you wish.
Treble is a voltage divider while bass and mid are wired as a variable resistor.

Quick check with a meter on power pins and also check the 3 positive inputs,, they should read close to half voltage,, your bias voltage.
Phil.

Yes, I powered U3 and also "disabled" the other opamp in the the second IC putting bias V on the + input and connecting the - input to it's output.
I'll check voltages, and also the wiring again.

This is what the pots do right now

Treble:  does nothing at all
Mid: behaves as a volume
Bass: Like the Mid pot but doesn't roll of the volume completely
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 05, 2018, 09:12:44 AM
Turn the test board/circuit around the other way and turn the schematic up side down.
NOW re track all the wiring again.
WHY? simple it forces your brain to reconnect all the nodes in a different way.
A good way to see if you missed something.
Phil
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 05, 2018, 09:45:06 AM
Turn the test board/circuit around the other way and turn the schematic up side down.
NOW re track all the wiring again.
WHY? simple it forces your brain to reconnect all the nodes in a different way.
A good way to see if you missed something.
Phil

Great suggestion, I'll do that, thanks Phil. Maybe I can also try to bypass the tonestack to check if the 3rd amp stage works as it's supposed to. I guess I should get tons of gain without the tonestack attenuation. That way I can narrow it down to a specific section of the circuit and double check everything there.

I don't have a problem redoing the whole thing if needed be. It's a complete mess anyway and this is about the learning process more than the end result
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 05, 2018, 11:08:16 AM
Bypassed the tone stack and it works, it's louder too as expected, but doesn't seem loud enough. If I put my bazz fuss pedal in front of it, it gets much much louder, so I believe there's plenty headroom in the preamp. Right now I have 1M for the input impedance.

On a side note, I like the tone a lot!

I'll check component values and wiring.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 05, 2018, 12:11:11 PM
I think I found the problem with the tone stack. I got the wire colors all wrong, duh!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 05, 2018, 10:52:24 PM
Don't worry the best learning tool is a mistake. :tu:
It's hard to blow up opamps so you will be fine.
With high current circuits like discrete power amp stages you have to be much more careful. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 06, 2018, 04:01:20 AM
Don't worry the best learning tool is a mistake. :tu:
It's hard to blow up opamps so you will be fine.
With high current circuits like discrete power amp stages you have to be much more careful. 8|
Phil.

Good to know, it wouldn't be a huge deal if I blew up an opamp, other than it probably would have me scratching my head trying to figure out what went wrong.
Anyway, I rewired the pots but it still isn't quite there. So I think I'm giving up on debugging this particular board. The tone stack is still all wrong. I'll try bypassing it, and increasing the negative feedback resistors (at least U3's) to experiment with those things and see how much more gain I can get from it, so I'll use it as a pure gain module. Then I'll breadboard the tone stack and that will go in another board somewhere. Probably where the power supply is right now, since the tone stack wires seem to be picking up an awful lot of noise from it and I'm running out of real state for the OD stage anyway.

But before I do any of that I'm going to do some reading on opamps
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 06, 2018, 12:35:25 PM
I've been playing it for a while today and it seems to lack some low end. May be the speaker, but I decided to try something: built an 8 ohm dummy load with a few 10W resistors in parallel, then used a function generator app and measured the RMS voltage at the output of the preamp. Here' what I got:

50Hz: 0V
100Hz: 0.3V
200Hz: 1V
300Hz: 1.8V
400Hz: 2.6V
500Hz: 3.2V
600Hz: 3.2V
700Hz: 3.9V
800Hz: 4V
900Hz: 4V
1KHz: 4.1V
2KHz: 4.2V
5KHz: 3.6V
10KHz: 2.2V

I've read I can increase the value of the coupling caps to get more bass, those are C1, C4, C9, C13 and C15, right? or is C6 also a coupling cap?

EDIT: upped C6 to 220nF and lost most of the signal, so that's going away
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 06, 2018, 04:13:05 PM
Success! I eventually upped all C1, C4, C6, C9, C13 and C15

Result:

50Hz: 0.8VV
100Hz: 1.6V
200Hz: 2.3V
300Hz: 2.8V
400Hz: 3.2V
500Hz: 3.5V
600Hz: 3.7V
700Hz: 3.8V
800Hz: 3.8V
900Hz: 3.9V
1KHz: 3.9V
2KHz: 3.9V
5KHz: 3.4V
10KHz: 2.1V

So it seems the -3dB threshold is somewhere around 150Hz when it was at a little over 300Hz before.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 06, 2018, 06:59:50 PM
BTW, I tested my crappy 3'' speaker response using the function generation app and anything bellow 250 Hz sounds like crap. No wonder the coupling caps mod seemed to make no difference to the listening. So I wired the output to take stereo headphones and plugged some good ones with proper bass, and man, this little monster sounds great!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 07, 2018, 12:29:14 AM
WTF? a 3 inch speaker has little chance, a banana might work better.  :lmao:

Re changing the response curves.
From what I understand you are building a preamp to run into a small low wattage power chip that is running on maybe 12Volts.

If so, then when you max out the low freq at the preamp then that little power chip has no chance of producing a balanced response. All that you will get is early distortion and mud bass when you crank it up loud. xP

If you want big bass you need a power amp with headroom and that means big PSU.
and you need to get a real guitar speaker of at least 8/10 inch in a cab otherwise you are getting a false impression of the real sound/tone produced.

To give example of what is going on;
Take a 1,000Watt pa setup,, It takes 700W to drive the low Fq, 200W mid band Fq, 100W for hi Fq.
It takes a lot of energy to drive low freq.
That is why a guitar player using a 30 Watt amp can sound as loud as the bass player using a 400W rig.

The classic Marshall Amps from years ago had little low Fq below 100hZ and took a dive up around 3 or 4khZ. that is called tone focusing.
All the energy is focused in that central area and gives much better clarity/Note definition.

Now most guitar crap has way too wide bandwidth and once you add all the dirt pedals it becomes too cluttered with harmonic crud. If you want great guitar tone limit the bandwidth. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 07, 2018, 01:09:27 AM
Here is a sim of the response curves of the Casino circuit.
note;
The blue trace is the output of U1b "mids are boosted" via the preceding network of R5,6 and C5,6,7.
If you want to hear the difference then just remove R5,6 and C5,6,7.
That will give you a flat response out of U1b.
This preamp is not high gain, it only has maybe +20dB (25dB at 3khZ) if you want to add more gain then play with higher values of R4 and R9. You can make R4 a 50k gain pot and it will distort.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 07, 2018, 07:05:49 AM
WTF? a 3 inch speaker has little chance, a banana might work better.  :lmao:

Re changing the response curves.
From what I understand you are building a preamp to run into a small low wattage power chip that is running on maybe 12Volts.

If so, then when you max out the low freq at the preamp then that little power chip has no chance of producing a balanced response. All that you will get is early distortion and mud bass when you crank it up loud. xP

If you want big bass you need a power amp with headroom and that means big PSU.
and you need to get a real guitar speaker of at least 8/10 inch in a cab otherwise you are getting a false impression of the real sound/tone produced.

To give example of what is going on;
Take a 1,000Watt pa setup,, It takes 700W to drive the low Fq, 200W mid band Fq, 100W for hi Fq.
It takes a lot of energy to drive low freq.
That is why a guitar player using a 30 Watt amp can sound as loud as the bass player using a 400W rig.

The classic Marshall Amps from years ago had little low Fq below 100hZ and took a dive up around 3 or 4khZ. that is called tone focusing.
All the energy is focused in that central area and gives much better clarity/Note definition.

Now most guitar crap has way too wide bandwidth and once you add all the dirt pedals it becomes too cluttered with harmonic crud. If you want great guitar tone limit the bandwidth. 8|
Phil.

Damn, makes complete sense.
The power amp is a 15W TDA7297 (http://www.st.com/content/ccc/resource/technical/document/datasheet/a3/eb/9b/59/dd/26/4a/27/CD00001048.pdf/files/CD00001048.pdf/jcr:content/translations/en.CD00001048.pdf), 32dB of voltage gain, driven by a  12 to 15V / 5A power supply which I think should be plenty. I initially planned on using a much smaller TDA7267A, but then I found out about that other one and went with the more powerful TDA7297. Not sure if that changes anything?

Unfortunately I don't have access to a proper cabinet to test the amp at high volume, but I might be able to borrow one

Any chance you can share the Spice file for the circuit please?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 08, 2018, 06:06:02 AM
Hi Dazz I just pm'd you.
Never had to export a spice file so this will be a experiment for me.  :lmao:
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 17, 2018, 01:31:12 PM
Well, the amp is finished and I'm quite happy with it considering it's my first build, I mean the thing is a mess but it works which is more than what I expected  :lmao:

I ended up using that gain pot in the first opamp as Phil suggested instead of adding another stage, & another board for the overdrive, just to keep is simpler, and I like the overdriven tone, it's definitely better than the OD of that MPF-102 JFET I built before.

The tone stack still needs work, not sure what but I'm missing something. It's usable anyway. The bass control works fine, although it doesn't have too much range. The mid works great but the treble is still behaving like a plain volume control. I'll see if there's anything I can do about that.

Thanks once again to all of you who helped me pull this off, specially Phil.

Here's a pic of my brand new Ghetto Casino 12. Please don't laugh
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 18, 2018, 04:39:00 AM
Who cares what it looks like,, it works Great to hear. :dbtu:

Re the tone controls; Here is a picture of the wiring.
As should be obvious if you want the mid in the middle you will have to work that out.
This way the wires just jump to the next pot.
If you notice a lot of the old valve fenders have the mid on the end easier to wire up I guess and less chance of mistakes.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 18, 2018, 06:56:36 AM
Who cares what it looks like,, it works Great to hear. :dbtu:

Re the tone controls; Here is a picture of the wiring.
As should be obvious if you want the mid in the middle you will have to work that out.
This way the wires just jump to the next pot.
If you notice a lot of the old valve fenders have the mid on the end easier to wire up I guess and less chance of mistakes.
Phil.

Excellent! that should clean up some of the wiring mess. Perhaps I can try bypassing the board's tone stack and moving it after U3 so that it's output goes straight to the volume pot hence saving another wire to the board (guess I'll need a coupling cap). That should make it easier to troubleshoot too
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 18, 2018, 07:15:16 AM
A bad move cause it's a Hi Z tone circuit and can't work into a 10k load.
If you want to hear how sad the outcome will be then just temporarily bridge R12 (1Meg) with a 10k resistor. Your tone controls will be rendered close to useless. :duh
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 18, 2018, 07:44:18 AM
A bad move cause it's a Hi Z tone circuit and can't work into a 10k load.
If you want to hear how sad the outcome will be then just temporarily bridge R12 (1Meg) with a 10k resistor. Your tone controls will be rendered close to useless. :duh
Phil.

Damn, I see. Thanks Phil.
So if I try wiring the tone stack like that, with those caps and resistors at the pots, the ones I put in the board (R11, C10, C11, C12) will be left floating. We'll see how that goes
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on March 18, 2018, 09:10:12 AM
You don't have to wire it exactly like I've drawn it up, it's just a reference to help you work it out.
Try using nodes,, that is how cad systems keep track of what connects to what.

Take the junction of R10 + C10 + R11 and call it Node 1, or make each node a colour.
Make Node 2, C10 + the top of VR1.
R11 + C11 + C12 can be Node 3.
Continue in that mind set and it will make life a lot easier.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on March 18, 2018, 04:16:13 PM
Un-friggin-believable, I figured it out! finally!
Turns out the volume pot was bad, but it seemed to be doing what it's supposed to do: control the volume  :lmao:
By just by sheer luck I accidentally poked it "the right way" as I was testing the amp for the emptienth time and bam! it worked for a split second.

Man it was driving me crazy. haha

How can a pot fail in such a misleading way? Do they have no decency? Won't somebody please think of the children?   :grr
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on June 26, 2018, 10:09:27 AM
I have an issue with the amp, not even sure if it just started happening or it always did it and I only noticed it now. It's making an intermittent, high pitched hissing/squealing noise at a frequency of 5.5KHz or thereabouts. I've ruled out power supply ripple by powering it with a pack of lithium batteries. I've been googling it and ordered some ferrite beads just in case, but I believe that won't help since it's supposed to filter radio frequencies well above those 5.5KHz. I've tried bypassing each of the 3 opamp stages in the preamp and managed to rule out the second one as the source of the problem, but when I bypass the other two, the whole thing goes nuts and starts buzzing real bad (oscillation perhaps?). I'm just about to try bypassing the entire preamp to make sure the problem is there.

I should mention I added gain pots for opamps #1 & #3 with switchable clipping diodes (asymmetrical) in all three opamps, not sure that's relevant but anyway.
Also the noise is there with no guitar, just the cable plugged in the input, but goes away if I unplug the cable.

Any ideas on how to troubleshoot it please?

ETA: I just connected the output of an overdrive pedal to the power amp's input and it's still doing the same thing, so I'm guessing it's not the preamp? But then again I also built that OD pedal so it might have the same problem (both layouts and overall build quality are atrocious TBH). I'll try a couple other pedals, I'm afraid also builds of mine...

ETA2: It's still doing it with the the other two pedals as preamps, so that seems to rule out the preamp entirely.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on June 27, 2018, 06:51:49 AM
Well it sounds like the power amp is unstable and oscillating.
As we have no idea of how you wired it up it's anyone's guess as to what has gone wrong.
Maybe post a schematic of the power amp you built and also a pic of the actual circuit.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on June 27, 2018, 09:45:36 AM
Well it sounds like the power amp is unstable and oscillating.
As we have no idea of how you wired it up it's anyone's guess as to what has gone wrong.
Maybe post a schematic of the power amp you built and also a pic of the actual circuit.
Phil.

I used one of these pre-built TDA7297 boards for the power amp (pic bellow)
The thing I tested a couple other small amps I have (the 1W tin can TDA67A based one and an aftermarket headphone amp) and those also do that annoying 5.5Khz intermittent squeal. I gets attenuated quite a lot if I touch the lead casing, so I'm guessing it's picking up some mains interference and maybe I need to double check everything is properly grounded. I'll see if I can test it somewhere else later today


(http://i64.tinypic.com/x5drvt.jpg)
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on June 28, 2018, 07:20:06 AM
Yep if touching the case effects the outcome then it's likely to be a grounding problem.
Now you have to go find out where? ;)
It's a good learning tool when these problems happen because once you work out what went wrong you will remember it forever. 8|
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 26, 2018, 08:34:33 PM
I finally got round to troubleshooting my grounding problems. I found that putting more pedals in the chain exacerbates the problem and it even starts picking up a nasty 120Hz hum from one of my switching power supplies. That happens even if that particular power supply is not feeding current to any of my pedals / amp.

Next thing I found is that the noise goes away almost completely if I connect the first pedal's input signal ground to the amp's chassis. Looks like a ground loop, right?

So I started googling and found this https://www.analogictips.com/faq-ground-rules-earth-chassis-signal-ground-faq/
where they recommend isolating the signal ground from the power ground. Right now I have all my power jacks center positive, with all grounds (signal and power) tied together and also to all every chassis (every pedal and amp) I thought that's how you implement a Faraday cage

I really hope I don't need to rewire everything to isolate signal and power grounds, not sure I would know how to do that anyway  :-\
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on July 27, 2018, 04:17:00 AM
You don't have an earth loop and you have not built a Faraday cage,, that is a different thing. ;)
More likely a Bad earth connection or a severely compromised one.
Without any details it's a guessing game from here. :-\

I can only offer some observations.
Most Pedal power sockets are normally centre common so I have no idea how you wired your circuit.  All this makes the situation even more complex.  xP

Also it seems you have more than one pedal supply which adds even more potential problems.

As to the dodgy ground path you have;
With power off go measure the resistance between common at the first pedal and amplifier common. It should read very low Ohms. 1 Ohm or less is good.
Then do it again with that wire in place, the one that reduces the noise. My bet is the meter will read lower with that wire in place. ;)

If that is the case then leave your meter connected to the Amp and keep probing each pedal common connection all the way back to the last pedal. That should tell where there is a bad common. Sockets and other connections can become dirty and and cause intermittent ground problems. Even the jumper leads can cause ground issues if they are worn out.  Even the plug itself can become mechanically weak and cause ground issues.

The input to most pedals use a stereo socket to turn on the power at the common connection of battery or external power and these can become compromised so lotsa places common or ground can become slightly lifted and cause hum.

Maybe post a pic of the whole layout.
Phil
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 27, 2018, 12:26:52 PM
You don't have an earth loop and you have not built a Faraday cage,, that is a different thing. ;)
More likely a Bad earth connection or a severely compromised one.

I'm on a roll! LOL. Well, that's good news because I guess it should be easier to fix

Most Pedal power sockets are normally centre common so I have no idea how you wired your circuit.  All this makes the situation even more complex.  xP

First thing I built was a fuzz pedal, a very simple one (bazz fuss) and I wired it center positive simply because the 9V power supplies I had lying around were center +. Then I built the Casino 12 amp and finally 2 overdrive pedals with spare components (one jfet based and one opamp plus clipping diodes, a simplified TS clone) It seemed to make sense to have it wired that way, with the enclosures grounded that I thought would help keep noise at bay. All pedals are true bypass.

Also it seems you have more than one pedal supply which adds even more potential problems.

I have two 9V and two 12V power supplies, but I'm only using one of each, one 9V for all the pedals, one 12V for the amp. All four are plugged to the same power strip even though I only use two at a time, that's to test noise with different combinations of PSUs

As to the dodgy ground path you have;
With power off go measure the resistance between common at the first pedal and amplifier common. It should read very low Ohms. 1 Ohm or less is good.
Then do it again with that wire in place, the one that reduces the noise. My bet is the meter will read lower with that wire in place. ;)

So weird, it measures very low resistance all the way through: 0.9 Ohms from the guitar to the amp chassis with all three pedals in the chain. Since the meter measures 0.6 Ohms with the leads shorted, that's 0.3 ohms along the ground path from guitar to amp.

I've tried different combinations of engaged/disengaged pedals and it gets even weirder: the chain is: Guitar -> OD1 -> OD2 -> Fuzz -> amp.
Well, if I engage the fuzz and disengage/bypass both OD's, I get noise from the (I guess poorly filtered) power supply.

Pretty much any other combination is fine, so looks to me like the fuzz (MPSA13 darlington transistor) with it's massive gain is amplifying noise picked up on the ground path before it. In fact, if I bypass the two OD pedals with a wire, the noise goes away for the most part even though they're disengaged (bypassed)

So yeah, I'm gonna make sure the ground connections in those OD pedals are OK.

The input to most pedals use a stereo socket to turn on the power at the common connection of battery or external power and these can become compromised so lotsa places common or ground can become slightly lifted and cause hum.

I'm not using that because I built those pedals to be used with power supplies, no batteries, so I didn't think that would be necessary.

Maybe post a pic of the whole layout.

I'm a bit embarrassed  to post pics since I built the OD pedals in tin cans and the whole thing is as ghetto as it gets, but I'll post a few of them if that helps
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 27, 2018, 05:51:04 PM
OK, I put a wire across both jacks in both OD pedals and the noise is gone almost completely.  :dbtu: I still get a little bit of it if I really crank the gain, but I'm pretty sure it's the guitar cable that's picking up most of it now (EDIT: yeah, I tried a shorter cable that measures next to no resistance and the PSU noise is gone for good). I guess some noise is unavoidable sometimes, although the suspect power supply could probably do with some better filtering. I tried putting a 470uF cap across it's output but it didn't do anything to make it quieter (it already has a 1000uF). I don't think I'm gonna bother with that. It's a cheap PSU anyway and it works well enough for home practice.

BTW, my Casino 12 preamp PCB's are on their way!
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 27, 2018, 06:32:52 PM
Damn, the noise comes back in all of its glory when I roll off my strat's volume pot... off to google this $%&t
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on July 29, 2018, 07:36:23 AM
If rolling the volume back on the guitar causes more buzz/hum then it's highly likely the guitar itself is at fault.
Better check that first before you blame the circuits you have built.
Continuity check the ground path inside the guitar first, don't forget the bridge is also grounded,, oh and the lead from guitar to first pedal.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 29, 2018, 08:14:03 AM
If rolling the volume back on the guitar causes more buzz/hum then it's highly likely the guitar itself is at fault.
Better check that first before you blame the circuits you have built.
Continuity check the ground path inside the guitar first, don't forget the bridge is also grounded,, oh and the lead from guitar to first pedal.
Phil.

Continuity seems fine, but considering that it also seemed right in the pedals and they were still poorly grounded, I'll double check the wiring and solder points in my guitars and cables.
I've done some tests and found something interesting... tried unplugging the guitar, so I have guitar cable (6 foot long) -> OD1 -> OD2 -> fuzz -> amp. Then I put a wire across the guitar cable to have it act as an antenna, and as soon as I fire up the noisy power supply, the 100Hz hum starts. But, if I plug the noisy PSU in a different socket in the same room, the noise goes away. That points to common mode noise, right?

Also, I put the noisy PSU back in the same power strip as the amp, the noise came back but... I don't get this... with the guitar still unplugged, if I ground the guitar to the amp, a good chunk of the noise goes away. If I put the tip of the unplugged guitar cable next to the pups, boom! lots of hum.

I guess shielding the guitar should help... and stop getting cheap PSUs too  :lmao:
I've been googling how to filter or shield SMPS's but that's a different story
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on July 29, 2018, 09:43:27 AM
Well that sounds like you have a Smode supply that is not meant for audio, only use those intended for audio or you will have a nightmare.
The hum is likely more of a buzz than a hum.

This page may help you understand the issue.
http://ka7oei.blogspot.com.au/2014/08/completely-containing-switching-power.html

I use 2 Smode supplies in my pedal board and one had to have some extra filtering, the page above will show you how if needed.

Oh one other possible issue when using power boards, plug the amp supply into the First socket (closest to the power source) and then the other supply into the second or last, that trick worked a while back for a chap who was having noise problems. It may or may not work here but give it a try.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 29, 2018, 04:10:37 PM
Awesome, thanks Phil.

I have some coils / chokes I cannibalized from the computer PSU I used for this amp, not sure they'll work though. The largest one measures only 6mH

I can maybe order one of these EMI filters (https://www.aliexpress.com/item/EMI-RFI-Filter-AC-250V-10A-CW1D-10A-T-Suppressor-Power-Line-Noise-Filter/32781939486.html?spm=2114.search0604.3.114.5e8c238f11VQoB&ws_ab_test=searchweb0_0,searchweb201602_4_10152_10151_10065_10344_10068_10547_10342_10343_10340_10548_10341_10696_10084_10083_10618_10307_10820_10301_10821_10303_10869_10868_10059_100031_309_10103_10624_10623_10622_10621_10620_525,searchweb201603_6,ppcSwitch_4&algo_expid=63a2cbc7-0d52-482f-8ff0-08c1c13b105f-16&algo_pvid=63a2cbc7-0d52-482f-8ff0-08c1c13b105f&transAbTest=ae803_1&priceBeautifyAB=0) for the mains, and see if I also need a DC output filter later. Besides, I don't think I should mess with mains considering my obvious lack of knowledge & experience.

I noticed KA7OEI mentions in his blog that he had already added bifilar chokes to both the AC and DC leads, and that took care of a significant amount of noise. How would that be done?

EDIT: I found an earlier blog entry there where he explains all that stuff http://ka7oei.blogspot.com/2012/12/reducing-switching-supply-racket-rf.html

And Here's a pic of the PSU in case it helps.

Comes with...

68uF input cap
1000uF output cap

jc817 optocoupler (https://www.addicore.com/v/vspfiles/downloadables/Product%20Downloadables/optocoupler_JC817/Optocoupler%20JC817%20Datasheet.pdf)

tl431 adjustable shunt regulator (http://www.ti.com/lit/ds/symlink/tl431.pdf)

uc3843 PWM controller  (http://www.ti.com/product/UC3843)

Two (I believe) power mosfets
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on July 29, 2018, 11:24:31 PM
Hi Dazz keep at it will work out. :tu:
I just used one of these for the mains side;

https://www.conrad.com/ce/en/product/521461/Mains-filter-IEC-socket-fuse-250-Vac-1-A-37-mH-L-x-W-x-H-60-x-45-x-335-mm-Yunpen-YL01T1-1-pcs

Comes with all you need in a compact unit.
the Capacitors in the mains filter have to be mains rated so that saves you a whole lot of research finding all the right bits and it saves space. Just make sure you wire the ground to the case of the chassis and verify with your meter that earth pin is actually connected to case. Some come with built in mains fuse and even some with on/off switch.
The DC output filter can be done with standard rated parts. As I'm always picking up E waste from junked electronics I had all the parts needed. 8)

Yes I found the filters worked without the need to mount it all in an isolated metal case. I have to put the guitar directly over the Smode before I can hear switching hash. Of course Ideally the 2 Smodes I have would be even better in a fully enclosed case but this works fine for my needs.

I had to join the two Neg terminals of the DC outputs on Both Smodes to reduce grounding issues. So I have one 18VDC Smode and the other is 9VDC. If you look I've also joined the negative side of both outputs to Mains Ground as well.
I posted this a while back but pics have gone??
https://www.ssguitar.com/index.php?topic=4092.0

But not to worry here is what it looks like right now;
(Copy pics to your viewer to get the whole pic)
(https://s5.postimg.cc/pmdbefg13/IMG_0585.jpg) (https://postimages.org/)
 
(https://s5.postimg.cc/yhe5oycjb/IMG_0586.jpg) (https://postimages.org/)

(https://s5.postimg.cc/3n6wr8emf/IMG_0587.jpg) (https://postimages.org/)

(https://s5.postimg.cc/cuz57xtef/IMG_0588.jpg) (https://postimages.org/)

Like most of my stuff it's always ongoing research so I'll clean up the wiring when I get time but I've been using this live for about 2 years now and it's given no issues. <3)

The 9VDC is in the corner while the 18VDC drives the Phatt Box only. That one gave me no trouble but the 9V needed the output filter to shut it up.
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 30, 2018, 04:00:41 PM
Hi Dazz keep at it will work out. :tu:
I just used one of these for the mains side;

https://www.conrad.com/ce/en/product/521461/Mains-filter-IEC-socket-fuse-250-Vac-1-A-37-mH-L-x-W-x-H-60-x-45-x-335-mm-Yunpen-YL01T1-1-pcs


Hmm, OK, I noticed that filter of yours has larger 3.7mH inductors which should put the -3dB cutoff at some 9KHz. The cheap ones at ebay/aliexpress with 300uH coils, according to LTSpice, have a much higher cutoff at 35KHz. I'm guessing I should probably steer clear of those

What a killer pedalboard! What does that Phatt Box do if I may ask?
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: phatt on July 31, 2018, 08:57:53 AM
I can't remember the exact inductance of the cores but I don't think it's over critical, the link mentioned 10~100uH. Just read the link as he mentions the exact value he used. 8|

As my pedals are all low current heat was not an issue for the cores. I do remember the inductors I had were a bit low so I simply joined 2 in series.

Re the Phatt Box;
That is 3 circuits in one box.
A compressor from member mictester (FSB forum) then a very simple diode clipper then a cab sim circuit based on a very old Nobels unit from long ago.

The PhAttBox by itself only has a subtle effect but in combination with the PhAbbTone and higher volume levels it really gives the impression of a much more expensive rig.
The aim was to be able to make a very basic clean SS amp (Namely my old Laney Keyboard amp) sound like a classic rock amp. The Compressor helps a lot as it can do a pretty good job of creating that classic triode rattle,,some call this the sweet spot on old valve amps where the amp is just starting to break up on bigger signals Or others call it the hair on the edge of a hard hit note or chord.

IME, distortion is easy to get but it's the in between edge that is much harder to get. Most compressor circuits run way too clean but this is more low fi and works well for guitar. So the more it compresses the more it distorts. Maybe not as good as the real thing but a huge improvement over a lot of compressor pedals on the market.
And simple to build. ;)
Phil.
Title: Re: Building a TDA7267A guitar amplifier with overdrive
Post by: dazz on July 31, 2018, 10:05:44 AM
I can't remember the exact inductance of the cores but I don't think it's over critical, the link mentioned 10~100uH. Just read the link as he mentions the exact value he used. 8|

Oh, but that would be for the DC output filter, right? I was referring to the mains filter, the aftermarket one.

As my pedals are all low current heat was not an issue for the cores. I do remember the inductors I had were a bit low so I simply joined 2 in series.

Actually I already have filters in my 9V pedal PSU's outputs, one of them is an RC filter that seems to work fine for low current pedals (mine are too, all three measure below 5mA). For the other one I used a 7809 because it was outputing over 12V even though it's supposed to be 9V.

The thing is that the PSU that is supposed to require filtering is one of the 12V 5A that I use to power the amp. The chipamp is limited to 2A, but I don't think I can build the filter ignoring current draw?

Re the Phatt Box;
That is 3 circuits in one box.
A compressor from member mictester (FSB forum)

That's the Really Cheap Compressor, isn't it? A great candidate for my next project  :tu:

distortion is easy to get but it's the in between edge that is much harder to get.

That explains why my crappy OD pedals sound like crap at low gain. They're OKish when cranked especially the JFET one so I ended up increasing the gain to get more and more distortion. AT first I added an extra gain stage, then put a switchable cap at the source of one of the sources... it started as a Professor Tweed OD from Run Of Groove, now its more of a nasty distortion/fuzz effect  :lmao:

I'm gonna have to try the compressor and see if I can get some of that magic here  too :dbtu: