Kevin - what else can you say about the the FQP sound? I plan to to build one with some FQP’s I matched up earlier this year for Aleph Classic group buy and my Juma F5 mini build, and I want it get my head in the game. What I think I learned this evening…
I did the chassis swap and added the filter. PSU voltage dropped a touch as expected. I needed a rebias. either this amp opens up with the rebias or after some time coming up to temp. My first chassis was a bench build, cook, bias, simmer, adjust, etc. Then I put it on real speakers and never turned it off. So it sat at temp and simply sang beautifully.
Did you keep your Harris and Fairchild or Onsemi both hot and just move RCA and speaker cables hin and forth?
Zoom out. Way out. Reflecting on the stock circuit - I think this is the biggest bang for the buck in our hobby. I sit back and laugh at megabuck power cords and interconnects looking for that last little bit of je ne sais quoi. Forget that. If your speakers are reasonably efficient, spend that $$$ on this kit and the rest on a few LPs and concert tickets. And use the stock power cord.
I'm still trying to decide if I prefer the my ACA Mini or my Racam. I think the latter just pips it, maybe a tad more in the LF that suits me. Built it with IRFP140N. Definitely would like try some more devices in the Mini.... which reminds me I never tried taking the jumper out!
But never forgrt the importance of high fidelity fuses! I saw some 100 dollar Furutechs the other day. Just gotta try those!!
Did not know this. Is it a feature of a newer version or should be set somewhere?
My ACA mini kit will soon jump on the bench
the real difference is Fair. jump IN that H2 were positive vs negative with Harris .
X jumper ouT Fair is half way then Haris IN /OUT that maybe can be done with difference resistor
There is one important fact to consider, regarding REW phase information. For our purpose, it's wrong by 180°.
Different logic is used for the notation of relative phase and negative phase is marked as starting 90° before phase of the reference signal and -90° is starting after reference signal.
So, REW measuring -90° H2 phase is not a negative H2, but positive H2. We want situation where REW displays 90° H2 phase.
Hopefully, this picture helps:
Don't know what is expected for ACA, but there are examples with REW measurements of amplifiers having confirmed negative H2 by design, measured as +90° H2. In example:
https://www.diyaudio.com/community/threads/diy-sony-vfet-pt-1.370282/post-6854181
https://www.diyaudio.com/community/threads/diy-sony-vfet-pt-1.370282/post-6854181
I'm silly happy with the sound of my ACP+, ACA Mini, driving Sony SSCS5 speakers in a desktop setup.
Dirty deeds too can be done dirt cheap
My 334 came quite cheap, and serviced in 2010 and barely used since. But I was lucky with that one.
My 334 came quite cheap, and serviced in 2010 and barely used since. But I was lucky with that one.
So, the "Prototype" amp with the Harris outputs sounds more like candy apple. The "REV A " amp with the Fairchilds sounds more like sour apple. 🤣
Give me a minute for a more serious answer. I'm going to do some listening tonight and I'll keep in mind that I'm doing a review. I just hate trying to put what I'm hearing into words...but I'll give it a go.
My second power supply came in so it will make swapping a little easier.
I bought the ACA Mini Essentials kit and parts from Mouser at least as good as the BOM. IMO the components that needed upgrading the most are the input coupling caps, C1, so 1uf Dynamicaps were used from my used parts stash. These were soldered on the bottom of the PCB for obvious reasons. An open chassis Mean Well 30VA medical grade switching PS (Mouser 709-RPS30-24 $16.65) plus a PO89ZB SMPS filter were used to start with.
Sounded pleasing right away! Running the amp 24/7 until 300 hours of break-in time. Today is day 5 - musical detail highly resolved now, better than the Schiit Aegir I sold! Deep base as long as I keep the volume moderate. Using a Chinese 30VA linear supply now. I won’t know if this is an improvement until I switch back to the Mean Well.
Mike on Audio thought a linear power supply sounded better – nice review.
Sounded pleasing right away! Running the amp 24/7 until 300 hours of break-in time. Today is day 5 - musical detail highly resolved now, better than the Schiit Aegir I sold! Deep base as long as I keep the volume moderate. Using a Chinese 30VA linear supply now. I won’t know if this is an improvement until I switch back to the Mean Well.
Attachments
^Interesting video^ Curious about the $300 PS he's using. Also curious about using a lab supply to power it.