DIY ACA mini

The one and only
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.375 is the value I use - the same as .38 as a practical matter. You can go a bit higher without trouble. Or lower.

- there is some initial drift from cold values as it heats up.

Anyway, what you have is normal, just trim it by halves after some warmup time, and again later until it settles in, and then leave it.
 
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Little hiccup. My bias will not stabilize. The difference between having the A/C on and not (but still cooler than not in the room) is .27v and .38v at the test point. I set it to .30v at what I thought was a good median temp (after hours of warmup). Will this thing run away, or will the heatsinks just get hot? They were at 60°C at .38v. Should I up R8 and R9 to 1 ohm?

I should note...that is w/ the amp being on all day. Just happened to check it and was shocked to see how high it had drifted.
what is your room temp this day ? t
 
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Thanks for the replies. I guess the problem is that there is some variance in my room temp and I cannot help that. I have 3 basic modes (and corresponding amp temps). Temp in the room probably ranges from 69 - 74 or so.

  • A/C on high = .26v
  • A/C on low = .30v
  • no A/C...just fan = .37

As long as that is fine at the highest the voltage drifts (.37), I'd say it's good to go! And honestly, it sounded best when it was really hot and up to the .5A bias!
 
Thanks for the replies. I guess the problem is that there is some variance in my room temp and I cannot help that. I have 3 basic modes (and corresponding amp temps). Temp in the room probably ranges from 69 - 74 or so.

  • A/C on high = .26v
  • A/C on low = .30v
  • no A/C...just fan = .37

As long as that is fine at the highest the voltage drifts (.37), I'd say it's good to go! And honestly, it sounded best when it was really hot and up to the .5A bias!
my will sound better with 30° in room :)
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Many Thanks to Nelson once again. This little amp is so much fun! I’m astonished at how good it sounds, but not entirely surprised because… Nelson.

105db speakers can certainly let this lil amp stretch its legs. I hid a P089ZB filter under it.
 

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music soothes the savage beast
Joined 2004
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Many Thanks to Nelson once again. This little amp is so much fun! I’m astonished at how good it sounds, but not entirely surprised because… Nelson.

105db speakers can certainly let this lil amp stretch its legs. I hid a P089ZB filter under it.
Blue led, must sound good :)

Any direct comparison to vfet?
 
In case anyone is casting about for connectors to use with existing banana-terminated speaker cables, and also want something that will go well with the Mini's petite theme, I'm very happy with these very slim banana-only female jacks. They accept up to 14ga stranded wire in the solder channel; 14ga also just fits in the Mini's wire blocks. I made these pairs up as pigtails, about 9" in length, which is a good distance to keep the existing speaker cables from pulling on the Mini.
P1040116.JPG

P1040117.JPG

They are available on Amazon (search for B083Z1ZBDV) and inexpensive.
Au-plated banana jacks B083Z1ZBDV.jpg
 
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As mentioned the first day...my initial impression was that it didn't give up much (if anything) to the the P-channel V-fet. Upon listening more, when this thing is hot...its 95% of the way there. There isn't quite as much "spooky" 3d factor going on as with the V-fet, but VERY close. And for something that takes less than an hour to put together and costs about 100 bucks...you can't go wrong! In my setup (highly inefficient speakers at 82db, but near field), it can go as loud as I could want. Haven't tried it downstairs in the main setup, but for a desktop system it's supreme!!
 
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Blue led, must sound good :)

Any direct comparison to vfet?
For me nothing does everything the vfet does, however with the jumper out, the mighty little mini ACA that could, does sorta have some of that vfet sound. It definitely can do the spooky wide floaty neg H2 thing. Swapping the jumper in and out while listening is a pretty drastic difference in sound. This little guy is VERY enjoyable!
 
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