91

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

« Last post by MRMNW on January 06, 2026, 04:41:02 PM »

Thank you. Including the VCAs?

I'm now getting 

V+ 4.59
V- 16.40

+12: 3.55
-12: .682

with no IC's in their sockets.

92

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

93

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.

94

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

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

95

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.

96

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…

97

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

98

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.

99

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

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

for reference

100

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