Amp Camp Amp - ACA

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aradan

Member
Joined 2015
moppy said:
Thanks for your reply but I can't find all the things I need in RS component.

For example they don't have R10 and R12 (332k ohms 0.4W and 68.1k ohms 0.4W)

Also Q4, LSK170, it seems can't get in RS component too.

Any idea where can I purchase online?
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68.1k depending on the precision.(note all resistors have tolernace). Meaning that your 68k at 1% precision can easily turn out to be close to 68,1k

You might use 68k instead of 68.1k or try to buy more of 68k and measure them.

I have used 68k instead of 68.1k in my builds. Out of 20 units easily got 3-4 of 68.1k which were stated as 68k

There would be no harm having the resistors which would have more power rating than required. As I have mentioned initially. I.e. you need at least 0.4w, any values up would do as well. As long as the size of the resistor would allow you to fit it in.



On the other hand you can try

http://mouser.com
element14 Singapore | Electronic Components Distributor | Premier Farnell Group

Fets are a different story you can try:

1. alweit via PM on this forum
2. Spencer
 
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maw503

Member
Joined 2016
Thump, need help, please.

Finished my ACA kit earlier today. First DIY project so I plugged them in, held my breath, turned them on and nothing. By nothing I mean no pops or smoke. I was a happy amp camper. Adjusted the bias and hooked them up. Listened for four or five hours. These amps sound really good and am sure will sound better over time. But when I turned them both off (volume all the way down, with pre still on) there was a loud thump from my speakers. I have a couple of other amps that I rotate in and out from time to time and have never heard this before. I'm using an acurus pre with pbj interconnects to the aca's, 10ga blue jean speaker cable and a pair of heresy II's. I've never used a class a amp before, so my question is, is the thump normal. Or could I have done something while soldering to cause this. I don't know much about electronics, the led lights up and music comes out, but I'm not sure all's well. Any comments, info, or suggestions would be greatly appreciated.
 
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maw503

Member
Joined 2016
Hi Zen Mod, thanks for your response. As soon as I flip the switch off there is a loud pop ( may be better description than thump) from my speakers. Mostly hear it in the woofer but also from the horns. I've used a sub before and when it was turned off it always made a soft pop/thump but was quiet enough that I was not very concerned. This is loudish and concerning. I take it that this is not normal for class a.
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
maw503 said:
Hi Zen Mod, thanks for your response. As soon as I flip the switch off there is a loud pop ( may be better description than thump) from my speakers. Mostly hear it in the woofer but also from the horns. I've used a sub before and when it was turned off it always made a soft pop/thump but was quiet enough that I was not very concerned. This is loudish and concerning. I take it that this is not normal for class a.
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what's visible bass excursion during that pop?
 
ChuckORWC

ChuckORWC

Member
Joined 2014
Perhaps I crowed too soon in my earlier post... I had only tested the right channel which worked. I assumed the left channel was working since it's all identical to the right, but that would be too easy, wouldn't it? So the left channel doesn't work... no output. :(

Checked all the solder joints, all good. Replaced Q1, Q2, & the sk170. Tested again. Still no output. Noticed that Q1 got very hot, very quickly. Q2 got hot but not blazing hot. Should both output FETs heat up at about the same rate?

Did not replace Q3 (ztx450) because I only have used spares which I'll have to desolder from an old board, but I suppose that's the next step. Then maybe swapping out caps.

Any other suggestions? Again, left channel is identical to the right channel, which appears to be working fine.
 
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tommydoan84

Member
Joined 2016
maw503 said:
Thanks xrk971, every bit of info helps.
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maw503: did you get the answer to your question "why the amp pop when turning off" ? I had the same issue with the amp too when switching off I heard a loud pop in my speakers even when volume is set to 0. I do not have this same pop sound with other amps that I have in my system.

I'm just checking to see if you found the solutions or maybe someone in this thread can help with the issue ?

Let me know,
Thanks,
Tom
 
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tommydoan84

Member
Joined 2016
I did some more research about amplifier pop when turning on and off and find this
"all amps pop and thump on turn-on and off, but they ussualy have muting circuits that delay output to the speakers until the Power supply is stable."
(Sources: What causes an amp to pop on turn on & turn off? No RCA's plugged in...still does it - Car Audio | DiyMobileAudio.com | Car Stereo Forum)

Realizing the fact that this is a very simple class A design which has no muting/delay circuitry and directly sources the DC unregulated supply voltage from the cheap external DC adapter made from China. I'm not surprised that the amp causes the pop when turning on and off.

What surprises me is no one had reported this pop sound issues besides me and maw503
 
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tommydoan84

Member
Joined 2016
Sorry for many posts on this Popping issues. I found a technical paper written by Texas Instrument by Mark Ginsberg explaining the technical background of popping sound at input/output stage of an amplifier and circuit design how to eliminate the POP.

Maybe this could be a design suggestion to Mr. Nelson Pass for another revision as an improvement to the ACA amp.

http://www.ti.com/lit/an/sloa108/sloa108.pdf

Thanks,
Tom
 
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maw503

Member
Joined 2016
Hi Tom, thanks for the information. I've found similar info also. xrk971 said his did not pop on start up or shut down, so I assume these amps are not prone to pop. These amps sound too good to think there's an assembly issue, so maybe it is the power supplies. I read a few pages earlier that someone had an issue with their's, but not sure what the issue was. Anyway, thanks for your help. I think I'll start looking for another power supply and see if that helps.
 
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tommydoan84

Member
Joined 2016
Thanks propitious for the reply and help!

maw503 said:
Hi Tom, thanks for the information. I've found similar info also. xrk971 said his did not pop on start up or shut down, so I assume these amps are not prone to pop. These amps sound too good to think there's an assembly issue, so maybe it is the power supplies. I read a few pages earlier that someone had an issue with their's, but not sure what the issue was. Anyway, thanks for your help. I think I'll start looking for another power supply and see if that helps.
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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 0.1 uF in parallel (across 2 terminal of the main switch). Will let you know if the pop goes away with this fix

Thanks
Tom
 
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Macfixer

Macfixer

Member
Joined 2011
mymacfixer.com
propitious said:
The turn off thump is well known and has been discussed many times in this thread. I do not know of anyone claiming the thump is so severe that it damaged their speakers. But if you think it is, read posts 1301 through 1303. As far as why ACA is designed this way, read post 636.
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Im sure way back that it was mentioned in a post that unplugging the supplies without turning off the amp with the rocker switch reduces this thump. Well thats what I do and it work for me so just dont use the switches...see if it works Im using with Fe206 so am aware it
 
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