Amp Camp Amp - ACA

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#9,542
There’s two reasonable answers to this -

1) Add a small fan, run it slow and silent.

2) Become a FAB* and leave and enjoy as-is.



* Fearless Amplifier Builder, a club founded by Nelson Pass, who’s motto is a quote of Nelson’s, “A little heat doesn’t scare us at all.”
 
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#9,553
Reversing polarity at the DAC won't achieve the desired result. The ACA creates the H2 signature and the polarity of the speaker must be reversed after that to create the expanded sound stage. For headphones, you typically must reverse polarity of the transducers so that a positive signal at the output of the ACA pulls the diaphragm away from your ear.

My theory is that a P-Channel version of the ACA would not require this reversal. The normal ACA squishes the top of the waveform at the output. A P-Channel version would squish the bottom of it's output waveform.
 
#9,554
chermann said:
Thank you Tony

As Mooly cleared this un symmetrical behavior is normally...maybe not so hard like i have....at the beginning of my journey
Click to expand...

Hello agin

after changing the NJFET from the clone pcb it was this K30A i implement the BF245B with Ids=7mA. BTW...the K30A are tested with 3,5mA and 4mA.
Watch out!! the BF245B has absolute other pin layout and you have to bend and twist this fet to get it correct into the correct setting.!!

additionally to this i ad a the psu cables some 820µF/50 rubicons in parallel to 10nF film cap to hopefully less noise from psu. i don hear anything from the amp because its very silent. but reading some comments about the premium parts and additionally information here in this thread i decided to do so. A very small 1µF/63V film cap i have left in my bench and i add this to the output cap in parallel.

after rebuild and setting the DC bias to 12,15V each channel i start to listening.
As i wrote in the last comments i was satified with this small amp in comparision to my other Class D (TPA3251EVM) and chipamps but the compressed center stage and the partly stress sound was not ok for me. the soft sound is general ok for me. after "burn in" my new loudspeaker i feel that i do not need all of the 5-6 Watt into my 4R speakers 😉. maybe i was so fascinated by the create sound of the new chassis( expensive scan speak)....and push more as needed.😀

How is the sound now? WOW!
Now the sound is very nice. absolute no noise...i thought i have i quiet amp but with the new N JFET its very nice to get a fine separation in the middle, very dark background and nice out swing of some instruments.yep thats very nice.

Thanks for your guidance !:nod:
chris
 
#9,556
really???

i did this before the N FET change because i read this by 6L6. i do not like the sound. it is in the first moment very straight and clearer but the "holographic soundstage" is not so fine...less bass

my chain:
laptop-Tidal master, Foobar, USB cable audioquest diamond- Gustard A20H DAC (XLR)- ACA -NADA DIY speakers (scan speak)
 
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#9,557
after reading the complete thread i will give you my sum up for actually active N-FET´s which are active in some stores:

Reichelt:
20 cent
J111 (up to 20mA)
J112(max 5mA)

SK117 about 70 cent (1mA ...14mA)

BF256B 32 cent (6ma...13mA)
 
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