Sound Skulptor forums
Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: SKa on March 06, 2025, 10:03:12 PM
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Hi everyone,
My name ist Stephan, i'm from Germany and i need your friendly help with a CP4500 problem.
I am not getting a signal at the output, obviously because I have incorrect measurements at the test points.
I did the voltages checks on Channel 1 PCB (A) first:
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Step 1.1
Mix = 100%
Ratio = 10
Attack = 0.1
Release =1.2
IN button pressed
HF lift, 100Hz, 50Hz buttons released
Negative meter probe on 0V
V+ = +15.9 VDC,
V- = -15.9 VDC,
+12V = +11.8 VDC,
-12V = -11.8 VDC
Everything good.
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Step 1.2
conditions plus:
Input signal = 0V
Threshold at +15
Makeup on 0
TP1 = 0VDC
TP2 = 0VDC
TP3 = 0VDC
TP4 = 14.9VDC !!!!
TP11 = 0VDC
TP12 = 0VDC
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Step 1.3
conditions plus:
Input signal = 0V
Threshold at +15
Rotate Makeup from 0 to +20
TP12 goes from 0 to -2.3VDC - YES exactly!
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1.4
Input signal = 0V
Makeup on 0
Rotate Threshold from -15 to +15
TP13: constant -14.6 VDC !!!
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At this time I stopped measuring.
I replaced U9 and U10 but unfortunately there was no change :-(
The PCB is Revision 1.4
Can you help me with this information or do you need more information?
Many thanks in advance and best regards...
Stephan
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TP13: constant -14.6 VDC !!!
Check that the DC voltage (from +12 to -12V) coming from the threshold pot gets to to R95 (left pin).
If not check the solder joints on the pot P1 and on the connectors CN1a and CN1b
TP4 = 14.9VDC !!!!
Check the solder joints on U9, U10, R36...R40.
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Hello JPK.
Thank you very much for your help!
And sorry for the delay... I had some personal work to do.
So I did, what you suggest.
- Re-soldered the connections on potentiometer P1 and on connections CN1a and CN1b.
- Checked whether the DC voltage from the threshold potentiometer reaches R95 (left pin): Yes, it is between +11.8 and -11.8 V.
- Re-soldered the connections on U9, U10 and R36...R40.
But unfortunately, it is still 14.9 VDC at TP4 and a constant -14.6 VDC at TP13 (as described above).
Do you have any other ideas? I would be very happy. Unfortunately, I'm not making much progress on my own.
Thank you very much!!!
Cheers...
Stephan
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Check if the voltage on R95 left pin moves with the Threshold pot. Should go from -12V to +12V
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Yes, it goes between -11.8 and +11.8 V.
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Do you confirm that TP11 is at 0VDC ?
If true there is something wrong arount U21 and R95 to R99. Check the resistors value.
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Hi JPK,
Thanks for your patience (I was on vacation).
And thank you so much for your help!!!
After checking R95 to R99 and not finding any errors, I focused on U21 (based on your suggestion). I had already swapped that one for one from the RIGHT PCB.
And, you won't believe it, BOTH OPA2134s were defective. I swapped one broken IC for another. That doesn't help, of course :-) :-)
Ordered two new ones... ZACK... everything works!
I would never have thought of it without you. Thank you so much!!!
Cheers...
Stephan
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(https://fonts.gstatic.com/s/e/notoemoji/16.0/1f44d/32.png)