About to start building a pair of ACA kits

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#22
You're going to love those ACAs! You definitely have a lot more building experience than I do, but one of the things I've enjoyed most about them is the ability to try different options so I'm curious why you are going to make yours permanently bridged? Not judging, just being nosy. 🙂
 
#28
this can't be correct, it seems too simple 🙂
the 3 position switch is eliminated so no wiring to it. the concept then is that the left board's "negative out" on the diagram provides the input signal - attenuated by the 39.2k resistor - for the right board.
those are the internal changes.
then just connect source input and speakers as per 1.8 guide for bridged mono.
ATTENTION EVERYONE! THIS DIAGRAM MAY BE ERRONEOUS! CHECK LATER POSTS FOR COMMENTS AND POSSIBLE CORRECTIONS!


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#29
If you plan to run them perma-bridged, advised to disconnect the XLR connector. If you ever run them balanced, you'll have the left channel being injected out-of-phase into the right channel. Might also want to consider a dummy plug for the right RCA plug (or remove it as well).
 
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#32
Great, thank you guys. And I will keep the XLR and right RCA jacks off the panel for now. Can't hurt for cooling and since it's the back panel will not degrade cosmetics 😉
And I am thinking of installing a couple of small 24v fans internally. Ambient is pretty hot here in Vegas in the summers. Really hot. For 6-7 months...

And probably I should delete the diagram I made? Now that I think of it, it looks too much like an "official DIYaudio" document, which of course it is not...
 
#34
First unit completed, powered up and no smoke!!
Bias was easy to set just a slight tweak on both sides to bring them up to 12.5 v. I will check them again after some hours of running time.
With my ear right up to speaker there is zero hum, zero hiss.
Listening now to music tracks output as mono, and the one bridged amp sounds fine on my Pioneer sp-bs22-lr test speaker.
After about 15 minutes running time I can keep my hand on a heat sink for only 3-5 seconds which I expect is normal.

Things I would do differently next time:
  • use stranded hook up wire 100%.
  • use a lot more heat shrink tubing and keep the wires shorter.
  • use lock washes everywhere possible.
Mods I am seriously considering. Seems like there is plenty of room in there:
  • adding a small 24v internal fan.
  • research what it would take to add a clipping indicator. I would not want to mod the case so maybe a bi-color LED would work for both power and clipping indicator.
As I was working I triple checked every connection and after mounting each component on the board, and only found one error: I reversed the polarity of one of the big 3300uf caps. My excuse is the ex dropped buy just as I was installing that cap and started immediately browbeating on me 🙁 Needless to say I called it a night at that point.
 

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#37
Been listening to the one bridged unit all day using stereo to mono cable from FIIO M11 Plus streaming TIDAL. Sounds excellent, so I decided to go ahead install the XLR input since the M11 Plus can output balanced, and I will add some heat shrink insulation in places that should have it...
 
#39
[[You should install the switch as well]]
Unfortunately it feels wonky, it clicks in all positions but hardly any movement of the toggle when pushing to one end. I don't trust it for the long term which is partly why I decided to forego it...
 
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#40
Is this the switch included in the kit from the store? I've never had an issue with the one the store supplies. It is not a large throw. Signal level so it doesn't need a lot of internal separation.

picture might be helpful. A video even more so.
 
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