1

CP4500 Stereo Bus Compressor / Re: Can't Trim 1st Channel

« on: January 30, 2023, 12:45:40 AM »

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.

2

CP4500 Stereo Bus Compressor / Re: Can't Trim 1st Channel

« on: December 14, 2022, 02:32:51 AM »

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

3

CP4500 Stereo Bus Compressor / Re: Can't Trim 1st Channel

« on: December 11, 2022, 01:08:28 AM »

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.

4

CP4500 Stereo Bus Compressor / Can't Trim 1st Channel

« on: December 07, 2022, 10:50:41 PM »

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