Amp Camp Amp - ACA

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Loudthud

Loudthud

Member
Joined 2007
The ACA shouldn't produce a turn-on thump although you might get one from the signal source. Current draw starts slowly because C2 needs to charge up through R7. At turn off a large current is flowing in Q1 and Q2 and there is suddenly no place for the current to come from. C1 discharges into the speaker. One solution is a large capacitor to prevent the supply from collapsing so fast. See post 1970 and the discussion just prior to it.
 
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tommydoan84

Member
Joined 2016
tommydoan84 said:
Thanks propitious for the reply and help!



maw503, no need to replace power supply. After doing some research on this symptom, i seem to find a solution:

"1. You can place a small value capacitor across the switch terminals
or
2. Put a metal oxide varistor (MOV) in parallel with the primary side of the transformer but after the switch."

I will try no 1. by soldering a small non-polar cap 10nF in parallel (across 2 terminal of the main switch). Will let you know if the pop goes away with this fix

Thanks
Tom
Click to expand...


Modification: adding a small cap might not be the ideal case since the capacitor will discharge the stored energy when the switch is on. MOV or RC circuitry is what you want to prevent this to happen. I read some other topics they mention 10nF x2 safety cap in series with 180ohm -220ohm , 1 W resistor.
 
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Loudthud

Loudthud

Member
Joined 2007
george_ct said:
Hello,
How can I reduce the bias of an Amp Camp Amplifier? Which values of the components should I change?
Click to expand...

Do you mean bias Voltage or bias current? Bias Voltage is controlled by the pot, P1.

Q3 controls the bias current. If you remove the 2.2K resistor that has been added between Q3's Base and Emitter, that will reduce the bias current to about 1 Amp.

If that's not low enough, you will need to replace R1-4. If you want to simply cut the bias current in half, simply remove R2 and R4. If that is too low, replace R2 with 1 Ohm 3W and R4 with 1.5 Ohm 3W. That will bring the current back up to about 0.75 Amp.

Output power into 8 Ohms will be reduced and there will be an increase in THD. If you are driving headphones, increase R1-4 by about 4 times. R1,2 to 2 Ohms 2W and R3,4 to 2.7 Ohms.
 
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zekeblue

Member
Joined 2012
Can anyone suggest which chassis from the diyaudio store (store rep?) would be the minimum in size and cost that would offer adequate heat dissipation when running the ACA amps at 24v? I would mount both channels in a single chassis (dual mono). Narrower than full width would be preferable if feasible.

Thanks,
.........Zeke
 
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rnjorge

Member
Joined 2016
As it is being mentioned, allow me to ask for an oppinion,

I have just finished my ACA kit (without the monoblock enclosures) and I was surprised as how well they perform with the supplied PSUs.

As I was waiting for my kit to arrive, I was planing on using a regulated power supply and going to the 24V "mod", but now I am wondering:

Does it really perform so much better in 24V as to justify the increased heat?

Thanks,

Ricardo
 
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thiagomogi

Member
Joined 2013
rnjorge said:
As it is being mentioned, allow me to ask for an oppinion,

I have just finished my ACA kit (without the monoblock enclosures) and I was surprised as how well they perform with the supplied PSUs.

As I was waiting for my kit to arrive, I was planing on using a regulated power supply and going to the 24V "mod", but now I am wondering:

Does it really perform so much better in 24V as to justify the increased heat?

Thanks,

Ricardo
Click to expand...

Yep!!!

Thiago
 
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Dennis Hui

Member
Joined 2002
Paid Member
zekeblue said:
Can anyone suggest which chassis from the diyaudio store (store rep?) would be the minimum in size and cost that would offer adequate heat dissipation when running the ACA amps at 24v? I would mount both channels in a single chassis (dual mono). Narrower than full width would be preferable if feasible.

Thanks,
.........Zeke
Click to expand...

I would consider the 3U mini dissipante:

Mini Dissipante 3U – diyAudio Store
 
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zekeblue

Member
Joined 2012
Dennis Hui said:
I would consider the 3U mini dissipante:

Mini Dissipante 3U – diyAudio Store
Click to expand...

Thanks, that helped me to focus. It does make sense as I see them now. It's narrower but still with substantial heatsinks. You think the height of the 3U is prudent over the 2U and the 300mm depth shouldn't be shortened? To put a another way, did you pick that particular variant of the Mini Dissipante line as being the sweet spot in size?

Thanks again.......
 
ernesternest

ernesternest

Member
Joined 2007
Paid Member
My ACA is housed in a 2U /300 Mini Dissipate. Powered by 19V,with R12, or R15 mod - I forgot, it never gets hot. I can permanently lay my hands on the sink. Powered by 24V, without resistor mod it shouldn't be much of a difference. I suppose, the ACA mono block uses a 2U /250 heatsink.
The only downside of the 2U /300 Mini Dissipante is, you have to rework the upper and lower guide rails, since the vertical dimension of the pcb plus fets is too big. An angle grinder is your friend.
Tonight I'll try the 24 V.

Cheers Ernst
 
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