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Author Topic: Building a TDA7267A guitar amplifier with overdrive  (Read 4624 times)

phatt

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #15 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.
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #16 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?
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Katoda

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #17 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.

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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #18 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

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phatt

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #19 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.
« Last Edit: January 12, 2018, 07:45:28 AM by phatt »
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phatt

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #20 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.
« Last Edit: January 12, 2018, 07:56:15 AM by phatt »
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #21 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
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #22 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:

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?
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blackcorvo

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #23 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.
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #24 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

« Last Edit: January 29, 2018, 05:57:08 AM by dazz »
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Katoda

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #25 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.
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blackcorvo

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #26 on: January 29, 2018, 09:06:21 AM »

I agree with Katoda, the plastic jacks are pretty good!
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #27 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.
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dazz

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #28 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
« Last Edit: January 29, 2018, 09:44:57 AM by dazz »
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blackcorvo

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Re: Building a TDA7267A guitar amplifier with overdrive
« Reply #29 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

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.
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