A single channel of the ACA 1.8 can drive a 4 Ohm load, otherwise it wouldn't work very well when bridged into an 8 Ohm load. It may sound marginally better with two channels in parallel, but the power won't increase very much.
In the M2 OPS thread there are talks of running lower voltage rails and higher bias. 12v at 2.5A or 17v at 1.8A both giving 30w dissipation. Similar to the 24v at 1.2A standard set up. Said to give more current and lower output impedance. Potentially better for lower impedance speakers.
Can the ACA be configured in such a way?
Can the ACA be configured in such a way?
I'm not sure its a good idea...
The FET's are very inefficient (lossy) running at a low supply voltage.
You are probably looking at around 1watt output into 8 ohm and a 2 watt into 4 ohm if you go as low as 12 volts. The high bias doesn't achieve much either because if you can't swing the voltage into a given load then you don't need the high standing current.
I would have thought the overall output impedance might have gone the other way (higher) when running lower supply voltage.
If you want to try it then its easy to do. The trimmer should have enough range to be able to set the correct operating point. To get higher bias you need to scale the 0.47 and 0.68 ohm resistors downwards such that your chosen bias current generates the required volt drop to turn on Q3.
Look for Tony Tecson's variant of ACA running at 48VDC, with the same current, exactly opposite to what you suggest, but will tick most boxes.
I think it's somewhere here in this thread.
Here's a schematic that Tony provided:
Attachments
Hello
Has someone created a tiny PCB to get rid of the turn on, turn off thumps ?
I’m aware that turning off the power on the AC side (power bar) instead of the 19-24Vdc side will work but I often forget to do so…
Nelson came up with a nice turn on, off suppressor but it’s presently sold at the DIYaudio store on a big PCB since it has extra components. See Here
Has anyone ever built the following circuit on a PCB ? Is there a Gerbers available?
Thanks
Eric
Has someone created a tiny PCB to get rid of the turn on, turn off thumps ?
I’m aware that turning off the power on the AC side (power bar) instead of the 19-24Vdc side will work but I often forget to do so…
Nelson came up with a nice turn on, off suppressor but it’s presently sold at the DIYaudio store on a big PCB since it has extra components. See Here
Has anyone ever built the following circuit on a PCB ? Is there a Gerbers available?
Thanks
Eric
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If an ACA should go in a Apple housing... 
A friend of mine want to have (as always) more power but his housing for the ACA 1.6 was too small. i tried my best to setup it because of bad thermal issues. it works but just with 24V.
so he shoot a cheap housing --> an apple PC housing G3 and my work would started.
LRS 150-36 is adjusted to the lowest level = 30,8V therefore the bias was about 1,5A each amp.
up to now the setup is optimised for 8R speaker impedance. wiht thermal past and ceramic isolators and cheap heatsinks on the MOSFET (IRF240) if got good stability and nice management.
sound is fine over my KEF R7.
measurements are: it has about 8R 10WATT and into 4R i just get 5WATT (more bias is not possible because of thermal issues.)
enjoy
chris
A friend of mine want to have (as always) more power but his housing for the ACA 1.6 was too small. i tried my best to setup it because of bad thermal issues. it works but just with 24V.
so he shoot a cheap housing --> an apple PC housing G3 and my work would started.
LRS 150-36 is adjusted to the lowest level = 30,8V therefore the bias was about 1,5A each amp.
up to now the setup is optimised for 8R speaker impedance. wiht thermal past and ceramic isolators and cheap heatsinks on the MOSFET (IRF240) if got good stability and nice management.
sound is fine over my KEF R7.
measurements are: it has about 8R 10WATT and into 4R i just get 5WATT (more bias is not possible because of thermal issues.)
enjoy
chris
Attachments
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ACA_31V_Apple housing.jpg -
signal-2023-11-02-19-40-58-635.jpg
Hi stanislav
yes you are right.
he said : " i am an idiot because i sold the other ACA boards" - (so he had 4 amps.!) i told him without big housing no modifications are possible (bias-heat-power) he is using some small ALR2 LS...and other 4R speakers.
my friend is very looking to his money and want to invest small amount of money (housing etc..) . Today we meet for a session.
ACA -ACP and changing supplies for the ACP...to show him what is possible.
actually i am off since years to mod may ACA´s...i go for some FW and now i try the APEX FX8.
kr
chris
yes you are right.
he said : " i am an idiot because i sold the other ACA boards" - (so he had 4 amps.!) i told him without big housing no modifications are possible (bias-heat-power) he is using some small ALR2 LS...and other 4R speakers.
my friend is very looking to his money and want to invest small amount of money (housing etc..) . Today we meet for a session.
ACA -ACP and changing supplies for the ACP...to show him what is possible.
actually i am off since years to mod may ACA´s...i go for some FW and now i try the APEX FX8.
kr
chris
Dear experts, I am the happy of the "Mac ACA" you can see on the pictures above, using a quality Meanwell SMPS. Wanting to improve things a bit further I am wondering whether to get two DC Filter Kits from Diyaudiostore and add them to the build or build a linear power supply from scratch as I have a 160 VA toroidal transformer lying around. Goal is ultimate sound quality and I am not sure which solution is gonna sound better. Any suggestions?