Amp Camp Amp - ACA

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Yes!! :D A Fugly! from mighty Zen Mod!
I'm gonna print that post and hang it to my wall! :cool:



I really like those little buggers. They're actually the most quiet amps I have around here currently. Dead quiet, no audible noise whatsoever. Perfect! They will definitely be my #1 amps in winter time, but now that my attic never gets colder than 25'C I might resort to something a little cooler :eek:.
 
The ACA is the first amp I have tried where an active pre-amp made a relative big improvement compared with a passive pre-amp. It probably has something to do with the construction. When you add a serie resistor (pot) you change the amount of NFB. But yes....it sounds ok with passive pre-amp but more silky treble (not as hard) and better defined bass using an active pre-amp. At least that was my conclusion after trying both.
 
I struggled through 25 pages of posts before I gave up.. I understand that a certain preamp (of which I don't know what it is) gives more and better bass. And that I will probably need an active preamp to get the best out of an ACA (more silky treble and better defined bass). But what active preamp?


I agree with this.
I am building a DIY preamp “kit” for this purpose called the “Forewatt” .

Meper- how much negative feedback does the ACA have...three or four DB?
I was under the impression this circuit had 0 NFB.
 
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I agree with this.
I am building a DIY preamp “kit” for this purpose called the “Forewatt” .

Meper- how much negative feedback does the ACA have...three or four DB?
I was under the impression this circuit had 0 NFB.


The NFB resistors are R11 (10k) and R12 (39.2k). So if you have 5 V out then approx. 1 V will be returned to the input. R11 and R12 are the dividers for the NFB.
NFB is an integrated part of the ACA design. It would nok work very good without NFB. I think bass control would be bad and response not very linear. Nelson Pass has open loop curves at FirstWatt pages for the ACA.
The first ACA version had less NFB. You can play with the amount of NFB to find out the difference in sound. Gain will be higher if you have less NFB and damping factor lower.
 
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Doesn't have BA-3 pre part have enough oomph to drive F4? This would be way too much for ACA. Use something with about 3x voltage amplification. It does sound pretty good with simple tube Pre, with Salas HPA used as a Pre. Whammy works.... One of Juma pre's. Lots of options for really good sound. There is not the one preamp for ACA.

Cheers, Ernst
 
It's not a kit, is it? I don't know much about electronics and would rather buy an integrated single ended class a amplifier in a shop, but I don't have the money for it. So I'm looking for other options to get what I'm looking for. I think it's rather strange there's an ACA power amp kit, but no pre amp kit to combine it with.
 
Oh I see old ACA V.1 have 14dB new ACA 1.5 have 10dB with more damping factor 10
 

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