Sound Skulptor forums
Build help and troubleshooting => CP4500 Stereo Bus Compressor => Topic started by: titotunes on December 07, 2022, 10:50:41 PM
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Hello, I just built my kit and was doing the calibration but stuck at step 7 (Adjust trimmer T1 in order to get absolutely no output level change when switching on and off with the IN switch.)
The trimmer for me has no effect. Also the IN volume is quite loud.
Here's my readings and photos of my board. Thanks for your help.
Voltages Checks
Channel 1
Step.....
Conditions
Result
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+ =+16.04
• V- =-15.98
• +11.93
• -11.77
1.2
Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Makeup on 0
TP1, TP2, TP3, TP4, TP11, TP12 = 0VDC true
1.3
Step 1 conditions plus:
Input signal = 0V
Threshold on +15
Rotate Makeup from 0 to +20
TP12 goes from 0 to -2.3VDC. 0 - 2.32
1.4
Input signal = 0V
Makeup on 0
Rotate Threshold from -15 to +15
TP13 goes from -1.8V to +2.8VDC. -1.178 - 2.82
1.5
Input signal = 3VAC
(measured between output XLR pins 2&3
with compressor bypassed)
Makeup on 0
Threshold goes from +15 to -15
• TP4 goes from 0.060VAC to 0.190VAC My meter isn’t sensitive enough. I see 0 - 0.1
• TP5 goes from +0.35VDC to a negative value -.21 - -2.34
• TP11 goes from 0VDC to -3.5VDC -0.22 - -2.74
• TP12 goes from 0VDC to +3.5VDC 0.23 - 2.73
1.6
input signal = 3VAC
Threshold on +15
Makeup on 0
Signal level (VAC) on
• TP1=1.5VAC, 1.3
• TP2=1.5VAC, 1.0
• TP3=1.5VAC, 1.3
• TP4=0.06VAC 0.0 (not enough resolution in my meter)
DC voltage (VDC) on
• pin 1 of U6 (white dot) = 0V 0.01
1.7
input signal = 3VAC
Threshold on -15
Makeup on +20
Signal level (VAC) on
• TP1=1.5VAC, 1.3
• TP2=0.4VAC, 0.8
• TP3=1.5VAC, 1.3
• TP4=0.2VAC 0.2
DC voltage (VDC) on
• TP11=-3.5VDC, -2.74
• TP12=+1.2VDC, 0.4
• TP13=+1.7VDC 0.95
(https://i.imgur.com/ukRJMs5.jpg)
(https://i.imgur.com/gCrfvZR.jpeg)
(https://i.imgur.com/1YXBm20.jpeg)
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1.4
TP13 goes from -1.8V to +2.8VDC. -1.178 - 2.82
The max threshold voltage doesn't go low enough. Check component value, solder joints and direction of U21, P1, R95 to R99, R36, R37.
The other deviations are probably related to this one.
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Hey sorry I made a typo in my readings before. Step 1.5 shows reading of 1.78 not 1.178. All other numbers are the same.
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Check the solder joints of U6, R54, T1.
After removing U6, check with your ohmmeter that the resistor between the 2 extreme pins of T1 varies from 0 to 1K.
Also the IN volume is quite loud.
Louder than when bypassed?
1.5
Input signal = 3VAC
(measured between output XLR pins 2&3
with compressor bypassed)
Makeup on 0
Threshold goes from +15 to -15
• TP5 goes from +0.35VDC to a negative value -.21 - -2.34
TP5 doesn't go to a positive value. Is it the same if you remove U9 ?
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Checked joints and orientation of U6, r54 and T1, no problems there.
T1 is measuring correctly 1k and sweeping.
When compressor is IN the volume is about 9db louder than when it's OUT. The trimmer actually does have and effect it's just minuscule. (about .2db difference)
When I remove U9 and do step test step 1.5 I get this value 0.21
Thanks
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When I remove U9 and do step test step 1.5 I get this value 0.21
Do you mean + 0.21V
1.3
Rotate Makeup from 0 to +20
TP12 goes from 0 to -2.3VDC. 0 - 2.32
Is it plus or minus 2.32V ?
The trimmer actually does have and effect it's just minuscule. (about .2db difference)
The trimmer normal action is +/- 0.8dB
1.6
input signal = 3VAC
Threshold on +15
Makeup on 0
Signal level (VAC) on
• TP1=1.5VAC, 1.3
• TP2=1.5VAC, 1.0
• TP3=1.5VAC, 1.3
• pin 1 of U6 (white dot) = 0V 0.01
Do you confirm getting a 9dB louder signal than bypassed?
This sounds impossible because the output voltage is equal to 2x the voltage on TP2 which makes 2VAC.
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Finally got it up and running. I had blown the safety resistor on the -12v rail, the zener diode protecting and the VU. Also the crimp connectors on the VU weren't making a reliable connection so I had to solder them.
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Great !