What's this?

[dan stanton]

Hi all. I am amking an amp similar to this peavey. What is the outlined section?

[Enzo]

It is a compressor/limiter. It prevents the output from clipping, essentially.

The signal at the output chip is samples and U2b converts that into a control voltage. That control voltage is used to control U4. The output pin of U4 is connected directly to the signal path going toward U2a and the power amp IC. SO when the control signal gets over a certain level, U4 starts to ground off some of the signal level.

it is pretty much invisible until you get to clipping. Then it compresses instead of clipping. Trust me, that sounds tons better than clipping.

[dan stanton]

Thanks for the answer, Enzo. Guess I'll have to rethink mine.

[Enzo]

If you don;t want it, ditch U4 and the parts around it, run R20 to ground, eliminating the 100 ohm resistor. get rid of the bridge made of D7-10, and all the parts around U2b. Now you don;'t have it.


That leaves U2b unused. Unless you find a use for it, ground the + input pin and connect the output pin to the - input pin

[Steve Conner]

Does anyone know what the part number of U4 is? My guess is a CA3080, the pinout and function match up.

The circuit is a compressor activated by the power amp's error signal, so it would probably be covered by Peavey's DDT patent. Does the amp have a DDT logo on it?

DDT is a great system and well worth having on a solid-state amp.

[Enzo]

It's a CA3094.

I never recommend removing it to the customers who want me to "remove that darn compressor." It does work well. But if the project is too complex...

[dan stanton]

Thanks again, Enzo. Mine is similar in layout, including the 2040.Opamps are
tl082. All datasheet design, so no copyright infringement. I'm going to leave out the compressor,for now. And use a 081 for U2.

[Enzo]

Copyrights wouold only be an issue if you were trying to sell your creation commercially. You can build your own home project any way you like.

If you want to look at similar designs that are simple, look at little guitar practice amps. Bass amps are more likely to be clipped, so they add this little circuit.