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CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« Last post by Denis on March 23, 2026, 08:46:32 PM »

I changed Q1 but that was not the issue
Did the sound return when Q1 was disconnected?

I see that R56 and R57 changed color a little.
This means you have a short circuit somewhere. Are they getting hot?

A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
You can check their value with your ohmmeter (in circuit).

Do you think it might be transistor or capacitor?
Not a capacitor. Neither a transistor if you got the DC voltages right in the picture here.

Hi Jean Pierre

I did some more digging. on ratios 2-20 the output does not change. as soon as the comp is in slam the output gets very loud, i think this is the volume it should be. And when I tap C9 quite hard I see changes in the volume. I swapped C9 out but no changes.

Work on Q1 did not change anything, with our without.

R56 and R57 are not hot or warm. same temp as all other components (excluding the walls of SK25, they are light warm as they should be i guess)

R56 has 6.6 Ohm and R57 has 7.6 Ohm

I checked the AC and DC Voltages all measured to 0V with 1VAC and XLR pin 2-3:

AC level on TP3: (measured first with 100mVAC on the input and it was around 1/10 of the now measured voltages)

• Ratio 2 : 25mVAC
• Ratio 4 : 50mVAC
• Ratio 8 : 80mVAC
• Ratio 12 : 133mVAC
• Ratio 20 : 230mVAC
• Ratio SLAM : 12.74 VAC

DC level on TP4: all on point

DC level on JMP1 pin 1:

• Ratio 2 : -0.2 to 1.7 mVDC
• Ratio 4 : -17.8mVDC
• Ratio 8 : -19.7mVDC
• Ratio 12 : -21.2mVDC
• Ratio 20 : -25.2mVDC
• Ratio SLAM : 2.79 VDC

TP6 6mVDC

TP5 on point

A 13,22VDC (crackle while placing the probe)
B -0.55VDC
C 13.8VDC
D -1.35VDC
E 15.6VDC
F -0.75VDC
G -15.9VDC

Thanks a lot for helping me

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 23, 2026, 02:12:37 AM »

I couldn’t get consistent voltage on a couple of the readings so I just decided to pull everything apart.  I made an incredibly stupid error and skipped over the last two diodes on the front panel pcb.  I couldn’t find the 1n914 diodes included but I had some 1n4148 diodes so I put them in their place at d10 and d11.  Testing seems to be going much better so far.  I know these diodes are almost identical so shouldn’t be an issue.  Will these be any problem?

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on March 21, 2026, 09:48:02 AM »

You could look for a continuity between ground and C8, C9, C10. But the best thing to do will be to shorten the pins.

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 18, 2026, 03:33:37 PM »

I did notice now that I forgot to trim the leads of T2 and that may have shorted to the case.  Is there a test while that is still soldered to check for issues there?

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on March 18, 2026, 12:14:19 PM »

I only get resistance from 0.3ohms to about 1.6Kohms
Normal because the trimmer is in parallel with R31+R32.

I have added some DC voltage checks to do here. Please compare with your values.

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 18, 2026, 02:54:25 AM »

R26, TR2 and R31 all look fine and no bridged pins etc.  The resistance on the 5k pots don’t test the way I would expect.  If I measure from the wiper to another pin on TR2 I only get resistance from 0.3ohms to about 1.6Kohms.  Not sure if there’s a problem there.  I tested between tp2 and tp3 again and the voltage swings from 2.7V to 3.1V and will never settle

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 17, 2026, 05:51:07 PM »

Sorry, step 7 was where I was hung up.  I could not match bypass on and off level.  I was reading 1VAC between pins 2 and 3 when bypass was up and 0VAC when depressed regardless of how much I turned tr1

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CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« Last post by JPK on March 17, 2026, 05:33:08 PM »

I changed Q1 but that was not the issue
Did the sound return when Q1 was disconnected?

I see that R56 and R57 changed color a little.
This means you have a short circuit somewhere. Are they getting hot? 

A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
You can check their value with your ohmmeter (in circuit).

Do you think it might be transistor or capacitor?
Not a capacitor. Neither a transistor if you got the DC voltages right in the picture here.

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on March 17, 2026, 05:23:21 PM »

I moved on and could not get past step 6
What happened at step 6?

Check the solder joints on R26, Tr2, R31.
Check the wire connections to the transformer, look for a thread that might be causing a short circuit.

I was checking for shorts anywhere and did find continuity between two pins on U3
Pins 1 and 2 are connected by a 7R5 resistor, whick way look like a short.

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CP5176 FET compressor / Re: My CP 5176 is very quiet on the input stage

« Last post by Denis on March 17, 2026, 04:17:02 PM »

Try removing Q1 on the broken unit. If the sound is back then Q1 is the culprit.

Hi Jean-Pierre

I changed Q1 but that was not the issue..any ideas what it can be? I dont want to swap out all pre stage
I see that R56 and R57 changed color a little. A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
I swapped the SK25 and the front assembly with no effect either. 
Do you think it might be transistor or capacitor? I would swap the caps out first.

Thanks
Denis