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Build help and troubleshooting => CP5176 FET compressor => Topic started by: Ptb on November 25, 2025, 07:07:08 AM

Title: CP5176 only compresses in 20:1 / SLAM mode
Post by: Ptb on November 25, 2025, 07:07:08 AM

I have a problem with my CP5176: it only compresses in the 20:1 (SLAM) mode. In all other ratio settings (4:1, 8:1, 12:1) there is no audible compression and the gain reduction meter does not move, even with high input level.

All calibrations have been done according to the manual and the values are correct. The unit passes audio fine and sounds good in 20:1, but the other ratios seem inactive.

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: JPK on November 25, 2025, 09:52:57 AM

Can you do the measurements shown in 4. Check the side chain in this page (https://www.soundskulptor.com/forum/index.php?topic=7.msg7#msg7)?

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: Ptb on November 26, 2025, 09:29:48 PM

Thanks, here are the measurements

AC level on TP3:

• Ratio 2 : 0.65 VAC = 3,3
• Ratio 4 : 1.3 VAC = 6,58
• Ratio 8 : 2.1 VAC =  9,04
• Ratio 12 : 3.4 VAC = 11,02
• Ratio 20 : 5.9  VAC = 11,69
• Ratio SLAM : 6.6 VAC = 9,56

DC level on TP4:

• Ratio 2 : 0 VDC = 0
• Ratio 4 : -0.5 VDC = -0,5
• Ratio 8 : -1.3 VDC = -1,3
• Ratio 12 : -2.5 VDC = -2,5
• Ratio 20 : -5.5 VDC = -5,5
• Ratio SLAM : -0.6 VDC = -0,6

DC level on JMP1 pin 1:

• Ratio 2 : 0.6 VDC = 0,7
• Ratio 4 : 0.9 VDC = 14,42
• Ratio 8 : 1.2 VDC = 12,3
• Ratio 12 : 1.9 VDC = 11,78
• Ratio 20 : 2.3 VDC = 9,17
• Ratio SLAM : 7.9 VDC = 13,8

DC level on TP6:
      -4.5 to -1.2 VDC depending on P6 = -13,2

DC level on TP5 with jumpers JMP1 on 2-3 and 4-5 [o o-o o-o]:
      0.32 VDC =  0,32 

A 12,7
B -0,6
C 13,3
D -0,2
E 15
F -0,8
G -15,1

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: JPK on December 01, 2025, 04:04:12 PM

With the same conditions as in 4. Check the side chain
What AC voltage do you get on U1 pin1 (1.4VAC) and U1 pin5 (0.7VAC) ?

Check the solder joints and value of resistors R25, R27, R33, R34, R35.

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: Ptb on December 04, 2025, 03:56:20 PM

Measurements: U1 pin 1 = 1.10 VAC, U1 pin 5 = 0.55 VAC.

I inspected the solder joints around U1 and the checked resistors; solder joints look OK and the resistor values (R25, R27, R33, R34, R35) match the values.

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: JPK on December 05, 2025, 11:44:30 AM

The problem lies around U1-U2, R33, R34, R35 and maybe R28 to R32.
The signal gain between U1-pin5 and TP3 should go from 1 to 9, depending on the ratio switch.
Your gain goes from 6 to 21. The gain is based on these resistors.

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: Ptb on December 14, 2025, 07:12:20 PM

Hi, and thank you for your help. I went through all the solder joints and cleaned up some of them. Everything is now working perfectly

Title: Re: CP5176 only compresses in 20:1 / SLAM mode
Post by: JPK on December 15, 2025, 09:44:20 AM

(https://fonts.gstatic.com/s/e/notoemoji/16.0/1f44d/32.png)