Amp Camp Amp - ACA

The ACA definitely sounds better with higher rail voltage and a corresponding higher 'bias' voltage at the Drain of Q1. Mine now run at 28V from a CRCRC filtered linear supply (300VA, 24V toroid) and 14.5V Drain bias. I use IRFP140 Mosfets at Q1 and Q2; others have reported great results with FQH44N10 Mosfets.
That's interesting because I wired mine as dual mono with a dual linear supply with an unregulated voltage of around 25vdc. The transformers are 18vac. I read that someone was using 30vdc with no ill effects. I have tried the bias voltage at 12.5v, but will see what a bit higher does.
 
Can anyone tell me what effect (good or bad) increasing or decreasing the voltage measured on the drain of Q1 from 10v for 19v PS or 12v for 24volts? I am just curious.
I plotted results of different set bias Voltages for the original 19V ACA version in post 576 of this thread. THD changes above 1KHz or so. When I ask if the rise in THD in the high end was a flaw or a feature, nobody answered.
 

hardyg

Member
2022-05-14 10:53 pm
I finished my 2nd aca amp just like the 1st (it works) and it does not work at all…I had to change out some resisitors that I was short in my kit (R11 10K 1ea short I got 10K 1/4 watt)..(R13 10K 2ea short…I got 2ea 10K 1/4 watt)…(R6 100ohm 1 ea short….I got 100 ohm 1/4 watt)…this is what diy audio told me toget…it acts like the wattage is wrong as I have quadruple checked everything….help???? is this the right resistance but the wrong wattage,,,should it have been 3 or 4 watts????
 

hardyg

Member
2022-05-14 10:53 pm
I had to change out some resisitors that I was short in my kit (R11 10K 1ea short I got 10K 1/4 watt)..(R13 10K 2ea short…I got 2ea 10K 1/4 watt)…(R6 100ohm 1 ea short….I got 100 ohm 1/4 watt)…is this the right resistance but the wrong wattage,,,should it have been 3 or 4 watts???? The left channel does not play at all no mater the dpdt switch position...Help plz...newb! aca amp2nd build (1st works//)
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It is the same question you asked 12 hours ago and you have 2 replies :)

The wattage is fine.

If the amp does not work at all then first check that the supply is present and correct (24 volts on Q2 middle pin). Check that you have approx 12 volts on R1/2/3 and 4. Confirm the FET's get hot.

Maybe post some clear pictures of your build too?
The boards and wiring.
 
Not sure if this is the right place to post this, but I'm pretty sure the holes are drilled in the wrong place on my amp's face plate.

When comparing to photos in the guide, there are a number of significant differences
  1. The holes aren't close enough to attach each side. I've loosened the side rails and wiggled them out as far as possible, the holes don't line up
  2. The holes are near the edge of the face plate. So even if I could attach the sides to the faceplate, the sides would be too far apart for the top and bottom to span. See the last image
  3. Also, the holes aren't threaded, it looks like they are intended to use with a nut on the oher side.
Is this clearly a dud? I bought the case and parts seperately, but that's beside the point - I can't assemble the case, part or not.

IMG-2659.jpg


IMG-2657.jpg
amp.jpeg
 
edit.....

anybody willing to take a pic of same front plate, to see screw holes?

as if both pairs are missing, at inner side of FPlate

FP is of proper size, as I see it, heatsink sides need to go closer, according to bottom/top plate size

editedit - now I'm officially confused - no M4 holes/taps on back side of FPlate, and there are 4 holes in corners

no such ones in pics above this post
 
Last edited:
I'm confused?
When was there an ACA front plate with exposed screw holes.
Wormboy, clearly something very odd with that particular front panel... return it for a proper replacement.

From the build guide for a picture of the normal internal screw places.
 

Attachments

  • LTdDtbOAxfPtd21q.jpg
    LTdDtbOAxfPtd21q.jpg
    38.7 KB · Views: 21
Last edited: