91

CP5176 FET compressor / Modification HPF cp5173

« Last post by PMswing on January 06, 2026, 04:34:27 PM »

Bonjour, est il possible de modifier (simplement) le HPF du cp5173 en le faisant passer de 80Hz à 160hz ?

Merci

92

CP4500 Stereo Bus Compressor / Re: Bad power voltages and reversed THAT1246

« Last post by JPK on January 06, 2026, 04:19:31 PM »

Remove all IC's from their sockets and check again.
If V+ and V- are correct, put the integrated circuits back in place, one by one, checking the voltages each time.
This will show you which one has failed.

93

MU524 Vari-Mu Tube Compressor / Re: Initial AC voltage jump

« Last post by JPK on January 06, 2026, 04:11:47 PM »

94

CP4500 Stereo Bus Compressor / Bad power voltages and reversed THAT1246

« Last post by MRMNW on January 06, 2026, 02:12:11 PM »

Hi,
I was getting bad readings in the first stage of the setup guide:


V+: .890
V-: 15.67

-12: .711
+12: .174

I checked everything over and realised the THAT1246 was in upside down.

I've since replaced the 1246 but it's the same - so I'm guessing something else has blown.

Not sure where to look,
Any help much appreciated.

95

MU524 Vari-Mu Tube Compressor / Re: Initial AC voltage jump

« Last post by CGMix on January 05, 2026, 06:27:18 PM »

Well damn, that was it. Transformer was upside down…

96

MU524 Vari-Mu Tube Compressor / Re: Initial AC voltage jump

« Last post by JPK on January 05, 2026, 10:06:16 AM »

Is the label on the transformer facing towards the back of the module?
Check the input transformer coils resistance (in circuit with potentiometer IN on 10):
pin2-pin4 : 37ohms
pin3-pin5 : 37ohms
pin7-pin9 : 98ohms
pin8-pin10: 98ohms
pin7-pin10: 194ohms

97

MU524 Vari-Mu Tube Compressor / Re: MU524 is noisy

« Last post by JPK on January 05, 2026, 09:46:42 AM »

Do you hear any crackling noise with the tube removed?
If not, I would try to replace the tube.

98

MU524 Vari-Mu Tube Compressor / Re: Initial AC voltage jump

« Last post by CGMix on January 03, 2026, 04:29:42 PM »

for reference

99

MU524 Vari-Mu Tube Compressor / Re: Initial AC voltage jump

« Last post by CGMix on January 03, 2026, 03:47:31 PM »

JP! Thanks for the reply. At TP3/4 I’m getting 3.9vac. On my other working compressor it sits at 1.8, I believe. I pulled the transformer last night, thinking I may have pierced R1, but I had not. Also, I’ll have to check again, but I think I was measuring about half a volt on each grid of the tube. And then it jumps up to about the 4V pretty quickly thereafter. I believe the Transformers is correct because it’s installed in the same manner as my other

100

MU524 Vari-Mu Tube Compressor / MU524 is noisy

« Last post by OttoWei on January 02, 2026, 11:13:52 PM »

Hi,

I have had this issue since I built the compressor, but I set it aside for a while. I’ve now taken the time to do a proper fault-finding session and would appreciate your guidance.

On startup the compressor is quiet, but after a few minutes it begins to crackle and gradually becomes more and more noisy. The crackling noise is only affected by the OUT pot. None of the switches affect it at all, and changing JMP1 has no effect either.

Here is what I have checked and observed so far:

• I have tried the unit in different lunchboxes.
• I have gone through the setup procedure again and all values seem correct, except for the following:
  
  
  • In step 6 (“Check that output voltage has risen to 3–4 VAC”), I measure 2.6 VAC with the OUT pot set fully counter-clockwise.
  • TR5 (ATN2) does not produce a clicking sound at the end position, although the trimmer itself functions correctly (step .
• I have re-soldered most of the joints at this point.
• Tapping on components has not revealed any intermittents or changes in the noise.

Please let me know if there are any specific areas or measurements you would recommend checking next.

Best regards,
Otto