Amp Camp Amp - ACA

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sr71castle

Member
Joined 2018
6L6 said:
The common (ground) connection is attached to the red speaker posts.

The actual output of the amplifier is connected to the black posts.

Because this amplifier circuit is inverting in absolute phase, if you connect your speakers to the amplifier red to red and black to black, absolute phase will be restored.

You are not the only one slightly confused by this, so it's totally worth explaining again. :D
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ecause this amplifier circuit is inverting in absolute phase, if you connect your speakers to the amplifier red to red and black to black, absolute phase will be restored.


Thanks for the time to answer. I will now solder the connections as shown to the red posts. It will be like the dairy queen blizzared test when they tip it upside down to verify it is thick. I always jump. May do the same thing when I power on the first time..........
 
Big Cheese

Big Cheese

Member
Joined 2016
Anand, I redid all pins on Q1 and Q2, they should be good.
Tried again, still the same problem...

MrAudioGuru & RNJorge, I did not wire in the rear switch, it is only stereo RCA, so that should not be a factor.

I am about to give up on these Q3 and Q4 and put in new ones. Can I use 2SK170 to replace the K170 on Q4? Should I replace Q4 on the other board as wel?

I will pack it in for today, see if I can continue with it tomorrow.

Thanks for all your help so far
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
Big Cheese said:
I took the non-cooperative board out and compared it to the left-channel board (which is working correctly). I couldn't see anything wrong, but I must be overlooking something...
Your review would be appreciated.
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I can't see anything obvious either I'm afraid.

If there is doubt over input switching then you could just wire each input directly to its socket to eliminate any errors

(I haven't actually built or handled one of these amps and so am not familiar with the specific instructions regarding input switching)


I see you just posted... if the current is correct in the 0.47/0.68 ohms (you've measured and it is) then Q3 is good.

Q4... small signal FET's can give odd results if faulty but its unusual. Have you tried applying a constant sine test tone (disconnect the speakers for this) and then measure the AC input voltage on the 'top' end of R11. Should be the same for both channels of course. Use a frequency in the 400 to 1kHz range. I'm assuming you haven't a scope.
 
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sr71castle

Member
Joined 2018
6L6 said:
Correct.

Stereo single ended, use RCA connectors on both RCA jacks and attach L and R speaker to the respective speaker posts.

Monoblock XLR, use the XLR jack and take speaker output from the two black posts.

Monoblock RCA, use the Left RCA for input, leave the right empty, flip the switch up, and take speaker output from the two black posts.
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Was looking for this. Was not sure how to hook up monoblock mode. Thank-you
 
C

cRomer

Member
Joined 2017
Mooly said:
You need to connect the meters black lead to the main zero volt (ground point) which is that common 'bussbar' connection at the back of the amp.


Make sure your meter is on DC volts and check the supply voltage on the middle leg of Q2 which should be 24 volts.

You should also have 24 volts on one end of R7.

Those are the first things to check.
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Hi Mooly

Both sides of the amp are heating up now and they have that 24 volts on Q2 and R7. All that is missing is the elusive sound.


Thanks again.

Ed
 
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cRomer

Member
Joined 2017
6L6 said:
cRomer - Great news! What changed and/or was fixed?
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Hi Jim,

Not sure. But yesterday before I took pictures, I removed both boards and rewired them so pictures would show clearer connections. Before I put them back, I did a bit of re-soldering on components. I re-install them and took pics that I uploaded to Rafa.

This morning I powered the amp on and felt a slight warmth touching this side of the amp as against the other one which was heated up after a few minutes. I removed the board again did some more re-soldering as recommended by nycavsr (Thanks Anand)

After putting it back it heated up evenly as with the other one. But still no sound. Shut the amp down. After a few minutes heard a slight pop from speaker and saw leds lit for a second with the front switch off. Got scared but switch it on and a loud pop from the speaker upon switching off. Long story short, found the black output wire is loosely soldered to the speaker binding post.

I will remove the other board and post more detailed pics now that some other members posted how to. :)


Thanks for inquiring.

Best

Ed
 
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Extreme_Boky

Extreme_Boky

Member
Joined 2003
Kwabbernoot said:
Thanks everyone for giving me some pointers regarding the loud buzz. Tomorrow I will try some of the proposed solutions.
I use the amp now with a chrome audio and I do hear a very slight buzz coming from the speakers. But I do like the sound of this little fella. It packs quite a nice punch.
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The buzz might be coming from the laptop (PC) switching mode power supply, via the common ground, all the way to the ACA... Try unplugging the power supply from the laptop, i.e. run the laptop on its battery.

Do you hear the buzz if there's nothing connected to the RCA sockets?
 
poseidonsvoice

poseidonsvoice

Member
Joined 2004
audiocircle.com/gallery/index.php?cat=48485
Paid Member
Extreme_Boky said:
cRomer,

I noticed that you did not use the middle distancer (any distancers) to properly position the PCB's - how far they will sit... away from the heatsink. You may have a solder joint and/or a wire touching the heatsink...
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He did. It is most clear in the third picture. It is a nylon spacer and is a clear color, not aluminum one like some of the other ACA kits. I ordered 2 sets as monoblocks so I received one of each kind.

Best,
Anand.
 
C

cRomer

Member
Joined 2017
Extreme_Boky said:
cRomer,

I noticed that you did not use the middle distancer (any distancers) to properly position the PCB's - how far they will sit... away from the heatsink. You may have a solder joint and/or a wire touching the heatsink...[/QUOTE

Hi Extreme_Boky

There are plastic distancers and maybe at least a little less than 1/4 inch away from the heatsink. I think I will have to say I am sure that no wire or solder joint touches the heatsink. I have not installed them yet to save time when removing the PCB while it is being fixed.

Thank you for pointing that out. Wish it were just the problem.

cRomer
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jhead

jhead

Member
Joined 2004
Starting up my build on the ACA 1.6 version. I have more then enough NOS Silmic 2200uf/35v that can drop in to where the output coupling position(3300uf/35v) is would this be unadvised and just be a outright bad idea? I wish to make this amp the best that it can be within reason
 
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CJ5 Renegade

Member
Joined 2011
short or what ???

When i power up everything works fine ..the leds glow and the speakers make sound...but when the boards warm up the psu crashes and cycles on and off.
tested seperately both boards do the same thing
tr4ied an other psu and it just crashes until unpluged and replugged in
i checked proper installation of all components and it all seems good
any thoughts on where to go next
thanks Harvey
 
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garybx

Member
Joined 2013
After completing my v1.6 build and setting the bias, the amp is working fine (I'll re-set the bias after it has warmed up fully). However, I just noticed that one of the bags contains leftovers - 4 small nuts and 6 small flat washers. I'm not aware of anyplace that they should have been used, especially since their quantities differ. Ideas?
 
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