Amp Camp Amp - ACA

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acowans

Member
Joined 2019
I used the illustrated build guide from the forum and am using the external 24 v power DC power supply specced with the kit, I bought it from the DIY site. I believe its the most current kit/set up avail from the DIY store. I made no mods to any part of the build, just used the BOM and parts provided and followed the excellent Illustrated build guide from the site. I turn on the amp by a front panel switch. I can pull the cover off and take a photo of the inside it thats helpful?

thanks
 
6L6

6L6

Moderator
Joined 2010
Paid Member
Switching the front panel is the DC side.

The sound is the output coupling cap charging. It’s normal. That sound is even in a video in the build guide. :D

acowans said:
... in the back of my nervous/paranoid audiophile mind I think it could damage tweeters at some point lol
Click to expand...

There has not been a report of any speaker damage, and there are a lot of ACA in the world. I’d not worry about it.
 
myleftear

myleftear

Member
Joined 2017
Paid Member
acowans said:
I built the amp, it works fine and sounds good for what it is, I don't trust/like that the initial rising pitch noise it makes when first powered (...) . The noise isn't very loud
(...)
thanks
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Others here have called it „the welcome fart“ ... unfortunately, I can barely hear it when I start my ACA (Same Version as yours)
If you want to suppress it, you‘d need to implement a soft-start of sorts, which seems to be „complicated“. Many recommendations and proposals in the thread.

Good 6L6 or mighty ZM (and most others too) are very knowledgeable...
 
6L6

6L6

Moderator
Joined 2010
Paid Member
Easiest way to not hear it is make 2 and run as bridged monoblocks. As the speakers are then not connected between ground and output, but between the two outputs, you don't hear the cap charge.

...it’s still doing it, you just don't hear it. :D :D :D
 
Last edited:
Alan4411

Alan4411

Member
Joined 2011
acowans said:
I built the amp, it works fine and sounds good for what it is, I don't trust/like that the initial rising pitch noise it makes when first powered on through the speakers, I'm assuming it's the caps (?). Is there a fix for this ? I'm just using the amp thru "expendable" desk top speakers. The noise isn't very loud but enough that in the back of my nervous/paranoid audiophile mind I think it could damage tweeters at some point lol

thanks
Click to expand...

It is C1 charging. It is a 'feature' not a fault and quite normal. Learn to enjoy it or build another ACA and run them in bridge mode...
 
thomasnadeau

thomasnadeau

Member
Joined 2010
acowans said:
I built the amp, it works fine and sounds good for what it is, I don't trust/like that the initial rising pitch noise it makes when first powered on through the speakers, I'm assuming it's the caps (?). Is there a fix for this ? I'm just using the amp thru "expendable" desk top speakers. The noise isn't very loud but enough that in the back of my nervous/paranoid audiophile mind I think it could damage tweeters at some point lol

thanks
Click to expand...

That is a common thing that was discussed earlier somewhere here. Apparently the wall wart DC supply struggles with the initial charging of the cap, and in some cases trips its protection a few times. You can avoid this by using a linear power supply. If you don't feel like or are iffy building one like the DIY Forum's PSU board (which is well designed and sounds great, but is a little challenging finding the parts list right now), you can alternatively purchase one just make sure it meets the specs needed for the amp (current/voltage/connector type and polarity).

For one of my amp camps I wanted to compare a ready-made PS with the wall wart to show my son a quick example of the differences. It works really well, and you do notice a big difference in the sound quality and dynamics. Since experimentation is one of the big points of this forum as well as learning how these things work, it might be worth a try. Not sure about forum policy for cross-posts so I think you can unicast me if you cannot find a suitable one on eBay/etc... and I can help you with that.
 
W

willcal48

Member
Joined 2020
Hi to you all ,and thanks DIY Audio and Mr Pass for this fantastic amp .I got the ACA 1.6 one.
Everything worked fine even though I am a newbe in the DIY field.
But there is a kind of noise in one of the channels sometimes almost inaudable then it goes up and down in volume and sounds like a storm from afar.Please help. .Any ideas?
Best
John
 
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