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Hoffman Amps Forum image Author Topic: AB763 One channel schematic question  (Read 2142 times)

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Offline acheld

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AB763 One channel schematic question
« on: September 24, 2020, 03:44:55 pm »
I built an AB763 (DR) several years ago, and I love the sound but now need a physically smaller amp.  And, as Doug states in the One Channel build, "whoever uses the Normal Channel anyway."  In theory, I would have used it; in practice, I just didn't.

So, I'm going to re-use all the expensive bits and rebuild as a Hoffman One Channel AB763 with 6V6's.

While going over the schematics for the Two channel and the One, I see that C22 (both schematics) use a .01uf coupling cap for the Two channel, and a .001uf for the One channel design.  Why would this be so?  On the Two channel schematic, there is the notation "Suggested value."  The original Fender design uses a .001uf cap in this position (I'm not sayin' this is better . . .).

Just curious.  My original amp used the .01uf coupling cap, and it sounds great.

Offline sluckey

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Re: AB763 One channel schematic question
« Reply #1 on: September 24, 2020, 03:49:26 pm »
...My original amp used the .01uf coupling cap, and it sounds great.
So why would you use anything else?   :wink:
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline acheld

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Re: AB763 One channel schematic question
« Reply #2 on: September 24, 2020, 03:57:38 pm »
Well, I won't do unless there is a good reason not to.

I was curious why Doug made that design decision.   

Offline PRR

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Re: AB763 One channel schematic question
« Reply #3 on: September 24, 2020, 04:32:22 pm »
0.001 seems small for "most" coupling-cap applications.

The input to a long-tail is one place where it is not too small.

0.01 or 0.001, about the same cost either way.

This is NOT important.

Offline acheld

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Re: AB763 One channel schematic question
« Reply #4 on: September 24, 2020, 05:11:40 pm »
OK, thanks.

Offline sluckey

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Re: AB763 One channel schematic question
« Reply #5 on: September 24, 2020, 08:37:30 pm »
The AA864 Bassman even uses a 500pF in that position.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

 


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