power amp questions

[Joe]

Ok, I am working on a design similar to this:
http://depalma.pair.com/Analog/analog3.jpg

I've built a couple of cap-coupled jobs, now working on a direct-coupled version in simulation. I want to add short-circuit protection, and I'm down to three options:

1. Forget it, and use the caps/single supply.
2. Use typical VI limiting and hope it works.
3. Place zener diodes from output to driver bases, hoping to limit the current to a known maximum.

Also, I can't guarantee that the bias won't shift very slightly with temperature. It's not much at all, but possible to get 1/8V or something if it gets really hot.

My first two builds (one 6W/channel stereo and one for headphones) sound nice and punchy, so I feel it's a design worth exploring a bit more.

[J M Fahey]

Hi friend.
Short answer: don´t waste time with it.
It isn´t even a working circuit, just a half-baked project still very far from its end.
It might work, even very well, but leave the development work to the designer.
Go for a regular, tried-and-true option.
Those LM3886 projects are powerful, cheap, and easy to build (and include both short and thermal protection).
I´ll soon post an LM3886 board *for guitar*, as I agree fully with Teemu that almost (all?) projects out there are HiFi jobs. Not bad at all, but not as rough as we need.
I´m personally using TDA7294´s, for the very $imple rea$on that I can buy them straight from the importer for a very good price but anyway I´ll buy a couple 3886, which seem to be easily available everywhere else, just to post the *built* project.
Bye.

[Joe]

Thanks for the reply, but I don't feel it's a waste of time to work on something new. I've already tested this and know that it's a great sounding circuit.

Back to the short protection, the zener diodes work in simulation, so I'll just do that and see if the amp blows up when I short the leads.

[teemuk]

That circuit looks a lot like the one used in Electro Harmonix Freedom amp. I think there should be a thread about it somewhere in this forum.

[phatt]

If you're just after a simple safety setup then hard to get past a PTC, Poly Thermal Capacitor,, well I think that's what they call em.
Certainly stops BJT's from going to transistor heaven when you make a boo-boo
I will never qualify at a SS guru but I find them a great help when testing stuff.
Cheers phil.

[joecool85]

Let us know how it goes, also I'd like to see the final schematic and maybe some pics.  Sounds like a neat build...I could use another electronics project