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

« Last post by vwyf11 on March 29, 2026, 07:42:40 PM »

When I installed the diodes I was able to get a solid 3v between tp2 and tp3.  After this step I had double checked the next day and am back to not being able to get a steady 3v from tp2 to tp3.  The meter bounces around from 2.4 or so volts to 2.8v.  I cannot even get to 3v anymore. I’ve ripped everything apart and double checked everything now.  Tried reflowing parts, nothing seems to be working.  

The voltage from 0v to V+ and V- both give me steady correct voltage.  

All the other tests on the page you link to are giving me results in the ballpark for the required voltages but all fluctuate around 0.25v up or down from the target voltage

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on March 27, 2026, 04:08:55 PM »

Remove U4.
What values (DC and AC) do you get on TP1 to TP4 in the initial conditions here.

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

« Last post by JPK on March 27, 2026, 04:01:52 PM »

D -1.35VDC
Something wrong here.
Check Q4 (BC550C), R11 to R15.

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MU524 Vari-Mu Tube Compressor / Low output voltage step 6

« Last post by Ben on March 26, 2026, 06:40:57 AM »

I am only getting 0.152v ac on the output when engaged. I believe the transformer is oriented correctly and solder joints appear clean. I am getting 0.14v ac @ U2 pin 4 and U2 has power. I hear the relay click when taking out of bypass. I also tried cleaning the tube pins. Please advise, Thank you
+15.6 v
-15.56v
B+ 45v
tube heater 6.15v and glowing

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

« Last post by JPK on March 24, 2026, 05:03:39 PM »

No problem, these diodes are very close.

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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.