I bought a non working aca amp from eBay for the chassis. I am putting a mono aca mini in it and have a question about the power switch. I wish to use the original switch for aesthetics, but that means I have to turn the amp completely on and off, no “stand by mode”. Will the humps,bumps,and thumps be intolerable? I plan on using the dpdt switch on back for switching the jumpers in and out. Anyone have a clever solution that I can’t see? Thanks for any help!
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The ACA has the 3300uF cap within the feedback loop whereas the ACA Mini does not. This allows the ACA to maintain its output as frequency falls... although there is a bit more to it than that.
The latest switching supplies we have from SL Power work great, but they occasionally have issues with power-up into the ACA mini power filter if the AC power is applied when the front stand-by switch is in the ON position. This is because the circuits of the switching supply test for the load value before committing to full power, and between the current draw of charging the big capacitors plus the bias on the amp the power supply might decide that there is a fault in the load.
This does not occur if the stand-by switch is in the "off" position when you apply AC power to the power supply. To avoid confusion, the switch is "off" when the toggle is to the left (as seen front the front). If the LED lights up continuously, you're fine. If it is pulsing, then the supply is not turning on properly.
Intended normal operation would have the switching supply always on (very little draw) and the front panel switch is used as the on/off switch.
If you give the supply a few seconds of AC before throwing the switch it works fine. If you fire it up the AC with the switch on and the light is pulsing, then you can turn the switch off, wait a few seconds and turn it on again, and it should be fine.
None of this affects the sonic performance. If you find this annoying, I will deliver a fix which involves changing a resistor value...
This does not occur if the stand-by switch is in the "off" position when you apply AC power to the power supply. To avoid confusion, the switch is "off" when the toggle is to the left (as seen front the front). If the LED lights up continuously, you're fine. If it is pulsing, then the supply is not turning on properly.
Intended normal operation would have the switching supply always on (very little draw) and the front panel switch is used as the on/off switch.
If you give the supply a few seconds of AC before throwing the switch it works fine. If you fire it up the AC with the switch on and the light is pulsing, then you can turn the switch off, wait a few seconds and turn it on again, and it should be fine.
None of this affects the sonic performance. If you find this annoying, I will deliver a fix which involves changing a resistor value...
That fix is changing R4 from 6.8K to 22K. It will slow the bias current turn-on time.
Use the nice looking power switch to control a DPDT relay to mimic the normal bias supply switch(es). DPDT because you're actually switching two different bias supplies with the two mono boards. Or.. if you want to custom wire that setup as well you could share the bias supply sourced from one channel as is done in the stereo ACA Mini and only need an SPDT relay.
ACA Mini Essentials Kits and ACA Mini Completion Kits are now available from the store:
https://diyaudiostore.com/collections/aca-mini
https://diyaudiostore.com/collections/aca-mini
w0ot! Thanks so much to Nelson, Jason, and team! I have the 'almost clone' and want to build an ACA Mini as a gift for someone.
Thanks for the information Mr. Pass. I will use front switch to turn on power to unit and leave it on, delete the xlr, mount a small plate, drill it and add another dpdt switch for the bias. Came to me last night during a fitful nights sleep. Just now ordered the kit from the store. Thank you very much!
So happy this kit is in the store! I managed to get an almost clone board and build one and now it will have friends 
I want o say how much I appreciate all that Mr Pass you're doing, followed by all the helpers because of costs involved I would have a stereo system as good as it is without this DiyAudio site and the teaching ability of its members Nelson, Jason, 6L6, the list goes on, um, and theres some character call Zen something reverberating in background where would we be with out him😉. (you only tease those you love) sorry if this sounds flowery,so ordered parts and looking forward to this build.
The only correction needed to what is listed in the store and on the BOM is that there are 4, not 3, 1000uF 25V electrolytic caps supplied for C4 and C5.
It's great that this amp is now available to everyone. It's a wonderful amp.
It also amazes me at what you are charging for it. Cheap. Buying parts from the BOM from a few vendors cost more than what you are charging for the complete kit.
Bravo.
It also amazes me at what you are charging for it. Cheap. Buying parts from the BOM from a few vendors cost more than what you are charging for the complete kit.
Bravo.
Check the BOM vs the schematic against the completion kit if that is what you ordered. The mono boards use different trim pots and could need an extra 6,.8k Ohm depending on how you choose to wire the bias and LED(s).