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Acoustic 370 Power Amp Sim Pedal

#22
johnk_10 said:
it's just a personal project at the moment, but if it sounds like I think that it will, I could probably build a few of them for others.
Click to expand...

Awesome! First there was the Viva 360+ preamp, and now there's this.

I sold my own 360 stack back in the early '80s. And I've often missed it. But now it's starting to seem like Acoustic Control's special sound may yet be reborn. And this time implemented as pedals.

How cool is that? :thumbsup:
 
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#23
johnk_10 said:
i'm putting a trimmer for the AGC gain in it for now.
I also added a mini momentary push button switch for S301 (AGC bypass) just like the original amp has. personally, I don't think that a toggle is what i'd want on the original amp or the pedal version of it.
R319 is a 680R in the original amp, and it sets the amp's overall bias ( & AC current draw). since I've rebuilt a LOT of vintage 370's, I found that putting a 1K trimmer in its place allowed me to adjust the amp to it's best sound so i'm adding this to the pedal as well. the later Acoustic 320's also have the trimmer instead of a fixed bias resistor.
Click to expand...

johnk_10 said:
yes. R304 is the offset adjust, you turn it so the output is exactly half the power supply voltage.
the 370 Schematic, Note 6 says: "ADJ R304 FOR SYMMETRICAL CLIPPING WITH A 2Ω LOAD AND S301 CLOSED (AGC DEFEAT)"
Click to expand...

If you increase R322 and R323 emitter resistors to 1K, you will be able to bias the output hot without worrying about burning up the final drive transistors. Since you don't need buttloads of current for a 2ohm cabinet, these resistors can be much larger.

Looking forward to the testing this weekend!:thumbsup:

-Frank
 
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#25
boomertech said:
If you increase R322 and R323 emitter resistors to 1K, you will be able to bias the output hot without worrying about burning up the final drive transistors. Since you don't need buttloads of current for a 2ohm cabinet, these resistors can be much larger.

Looking forward to the testing this weekend!:thumbsup:

-Frank
Click to expand...
yeah, i'm going to put the 1K's in there.
do you think that it should have the zobel network?
 
#26
I got the main power amp board built up, now I just need to build the two daughter boards (input amp/AGC gain circuit & +18V/-18V charge pump board) and get to testing it.


main PCB:

370PCB-02.jpg
 
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