Author Topic: Channels keep becoming unbalanced

December 05, 2023, 12:08:17 AM
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tvesneski

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I bought the CP4500 secondhand, so excuse my lack of knowledge on the build. My problem is the right channel keeps getting a boost in level. It seems like it has a little quirk - I'll turn T3 ever so slightly and it fixes the issue, but I'll come back the next day and it's back to being unbalanced. I've gone through the calibration steps and it works great when it's stereo matched. I really am not sure how to approach this issue so any advice would be greatly appreciated.

Thanks!

December 05, 2023, 10:28:27 PM
Reply #1

Dolbah

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This is funny, i buildt mine a couple of years ago and today i realized it is now ublanaced. First post i see in here is this :) +1
My issue is that whn i start calibrating the unit from start, i can not get T1 on channel one to match the 3.0 VAC signal that is present when i standby. T1 only manages to increase the voltage to 2.595 VAC.

Edit: and on channel two board i can't get T2 og T3 down to 2.595.

Sorry, did'nt mean to hijack this tread, but since we are in the same boat, lets see what JP says
« Last Edit: December 05, 2023, 10:59:35 PM by Dolbah »

December 06, 2023, 04:06:19 PM
Reply #2

JPK

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@tvesneski
It could be a damaged T3 (Mouser 3266X-1-201LF)
Or an intermitent solder joint. Reflow any bad looking solder joints.
JPK

December 06, 2023, 04:10:25 PM
Reply #3

JPK

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@Dolbah
Do you get TP1=1.5VAC with 3VAC at the input?
Are the VCA's socketed or SMC?
JPK

December 07, 2023, 07:47:03 PM
Reply #4

Dolbah

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@Dolbah
Do you get TP1=1.5VAC with 3VAC at the input?
Are the VCA's socketed or SMC?


@JPK



3.0 VAC source signal gives me 1,492 VAC on TP1.

With T1 turn on max, it gives me  2.709 VAC on the unit output.


My VCAs are in sockets

EDIT:
I realized now, that when testing with only board 1 powered, i get the above results. As soon as i power both boards, board/channel 1 suddenly gets a bump and is suddenly outputting 2.95 VAC
When removing board 2, it goes down to 2.7 VAC.

EDIt 2:
I had a bunch of OPA2134PAs laying around, so startet switching them. When replacing U212, i finally was able to match the bypass and active signal. But i have no chance of getting T4 to trimm the meter to 12 dB attenuation (worked yesterday).
Also noen of the trimmers on board 2 is reacting. And i feel the threshold is very sensitiv. Lets close my apperance in this thread, and start a new one. --> https://www.soundskulptor.com/forum/index.php?topic=422.msg2350#msg2350
« Last Edit: December 07, 2023, 10:28:21 PM by Dolbah »