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?

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

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

Quote from: 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.

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?

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

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

The section labeled "3x stages" is supposed to be replicated 3 times in series, right?

Thank you Steve, of course that helps, a lot
I've been googling for preamps and found this one, 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!

Quote from: 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.

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/

QuoteA 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

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

Quote from: 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.

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

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

I forgot to mention what I have planned for heat-sinking:



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?

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:



I'm also in the process of building a Bazz Fuss V3 pedal so I thought I could put that little circuit in the amp to have an overdrive "channel"



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