Amp Camp Amp - ACA

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The ACA has a 10k input impedance and so any active preamp should have no trouble driving that.

What I would say is make sure the preamp has enough voltage gain because the voltage gain of the ACA is extremely low. I'd say you need something around '10' as a voltage gain (20db gain)
What I would say is make sure the preamp has enough voltage gain because the voltage gain of the ACA is extremely low. I'd say you need something around '10' as a voltage gain (20db gain)
I would say it really depends what speakers one uses, their impedance and sensitivity.
I run a lightly modded ACA with a B1 as a pre. As we know B1 is a buffer, gain of 1.
But the speakers that I connect to it are 93 - 95 dB, 8ohm, plenty of volume, plenty of grunt.
I also tried for some time the ACA with a 12AH7 pre with gain of 10 with the same speakers. Volume control (the pot) needed to be between at 8-9 o'clock most of the time. Not a good combo.
So I guess 86dB speakers might benefit from a pre with high gain but the main thing is your speakers will tell you what pre you need.
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Would the Mean well RS 150-24 power supply be considered an upgrade over the standard aca mean well power supply?


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That particular chassis mount SMPS wouldn't necessarily be an upgrade over the ACA kit brick style on its own. What you do with the rest of your build could be an upgrade. The bricks were well chosen for this task.

Those chassis mount SMPS can take some external capacitance on their output. You could try a simple CRC or CLC filter. There is a potential to improve power delivery. A lot has been written on this topic in the DIY VFET amp, part 2. You might hear a startup noise due to the supply hiccup feature for starting into larger capacitance. Whether there is an overall improvement with this configuration is up to you.

I tried using one of the 27V Meanwell chassis mount supplies in one of my Hafler chassis ACAs. The ACA boards I'm using have CRC filters to the tune of 10,000 uF > 0.1 Ohm > 10,000 uF. The SMPS seemed to perform fairly well, but I prefer the sound of the linear supply that have built for these amps. The linear supply performs best at lower frequency extension and definition.
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Thank you for your reply. I think I’d like to peruse the linear power supply option. Is there a DIY BUILD GUIDE or thread that would help have a BOM and guide me through the process of building a linear power supply? Would the universal power supply boards in the DIYaudiostore be a good starting point. Or, could you recommend and a viable retail version?
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Hi, I like to share my ACA build for headphone: using IRF830. (This FET needs higher gate stopper)

I have it running for now at 330 mA, case stays cool.
I have a NVVV power supply, RC per channel of 0,25 ohm/3.300uF.

Works like a charm. I have 0.47 uF input and I have 470 uF output, all to reduce the turn-on thump.
I have speaker output too so I can use it for bi-amping if needed; then the ACA can be revved up a bit to say 500 - 600 mA and deliver 2 watts in 8 ohm.

bandwidth @ 50 ohm (my Fostex RP phone) is < 7 Hz - 270 KHz.

I have the 2k2 attenuation of the bias. So it gives lower output impedance. test: Moving from 51 ohm to 7 ohm (parallel the 8 /51 ohm) gives a drop of less than 1 dB. [It is a great amp for sensitive fullrangers]

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Hey, hows your headphone mod, I'm planning to do a ACA for headphones as well. What did you change in the end?
Hello team,

This is my first try at building a amplifier, almost all parts where sourced locally. Assembled PCBs were bought by a friend of mine. Used CAD to design some chassis around heat sinks.
Using Meanwell SMPS 24v 8.8a to power these.

I just finished building both of these, I have few questions:
  • I have used a 2watt 39k resistor on for the switch, will it make a difference for not using 0.25w?
  • One heat sink gets warmer than the other, bias and voltage is corrected. 24v and 12 for bias. (Yet to try the 2nd amp just finished it yesterday)

I am a noob at all this, yet trying to learn as much as I can.

Here are some pictures:


Maybe good to use some large shims to secure output devices to even out the pressure on the devices?
I was thinking if it was a good idea to rotate the PSU 180 degree to have much shorter mains wires to the PSU?
Now mains wires pass very close to the one amp board. The magnetic fields can introduce some hum to the amp.........
Generally a good idea also not to have signal wires close to the Meanwell PSU transformer.
I think the reason this question was asked was that looking at the pictures it looks like some kind of "gum" is used (blue and white).
Maybe it is an optical illusion......

yeah, same parts used accross.
I tested the other amp, and it evenly dissipates heat on both heatsinks.

@charles34 I am using Soundartist LS3/5a with these amps, and they do drive them.