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MU524 Vari-Mu Tube Compressor / Re: Stuck on step 7

« Last post by soundguy937 on August 18, 2025, 03:39:35 AM »

UPDATE: my DMM keeps fluttering between 1-4vdc in small to large increments between tp1 & tp2. All the other prior tests seems to be working correctly. 

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MU524 Vari-Mu Tube Compressor / Stuck on step 7

« Last post by soundguy937 on August 18, 2025, 02:42:02 AM »

Got to step 7 with my latest kit and the voltage between tp1 & tp2 keeps jumping up and down by hundredths of vdc. I did let the tube warm for at least 15 mins before testing. What would cause the voltage to flutter? Is it possible it is the tube?

Thanks

P.S. I got the U6 part for the stereo right kit today, Thanks a million

83

CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by JPK on August 17, 2025, 09:04:51 AM »

It is now necessary to sort out the bad chips. This is what I would do:
- Check that the diode bridges BR1 and BR2 are in the correct direction.
- Remove all the IC's from the PCB (U1 to U9, U21, U22).

- Insert the first THAT1246 in U1, power, wait until you are sure it doesn't get hot. Check that the DC voltage on TP1 is close to zero  (less than 10mV).
- Do the same with the second THAT1246.

- Insert the first THAT1646 in U7, power, wait until you are sure it doesn't get hot. Check that the DC voltage on pin1 and pin8 is close to zero  (less than 20mV).
- Do the same with the second THAT1646.

- Insert the first OPÄ2134 in U6, power, wait until you are sure it doesn't get hot. Check that the DC voltage on pin1 and pin7 is close to zero (less than 5mV).
- Do the same with all the other OPA2134's.

84

EQP501 Passive Equalizer / Re: Son faible et pas d'EQ

« Last post by JPK on August 16, 2025, 06:39:30 PM »

avec le switch SW3 on, entre R21 et 0V je lis 11M ohm
Pouvez-vous refaire ce test avec la LED court-circuitée ?

Mais maintenant quand je court-circuite Q1 le son se coupe completement alors qu'avant ca activait l'EQ
C'est un autre problème. Vérifiez le DOA, les connexions entre PCB.
Vérifiez que vous avez du signal sur TP1 (avant EQ) et sur TP2 (après EQ).

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MU524 Vari-Mu Tube Compressor / Re: Stereo Right Kit

« Last post by JPK on August 16, 2025, 06:18:04 PM »

It was mailed on August 7. It shouldn't be long now.

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MP573 Microphone preamplifier / Re: MP573 LED not behaving correctly

« Last post by JPK on August 16, 2025, 04:29:49 PM »

There are plugins for that.
Also https://www.soundskulptor.com/en/content/12-download-useful-links

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EQP501 Passive Equalizer / Re: Son faible et pas d'EQ

« Last post by Pierro on August 16, 2025, 01:47:31 PM »

J'ai verfié les soudures et elles ont l'air bonnes, avec le switch SW3 on, entre R21 et 0V je lis 11M ohm...
Mais maintenant quand je court-circuite Q1 le son se coupe completement alors qu'avant ca activait l'EQ. Aurait il cramé entre temps?

88

CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by Gian on August 16, 2025, 01:17:25 AM »

with no input signal

with control panel (front) board pulled and with U7 pulled out and U6 pulled out
TP2=1.192VDC

Wth U7 pulled and U6 inserted
TP2=-16DVC

I have built over 16 different 500 series mic preamps and at least 8 500 series EQs and Compressors. I am very careful with placement and soldering.

What can I trace to see where this is coming from?
What are my options here?

Where can the -16VDC be coming from? I have checked all solder and washed both sides of the board.
I don't know what else to do.

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MU524 Vari-Mu Tube Compressor / Re: Stereo Right Kit

« Last post by soundguy937 on August 15, 2025, 07:21:36 PM »

How soon should I expect to receive the part?

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CP4500 Stereo Bus Compressor / Re: CP4500 Cannot level match and incorrect voltages in step 1.6

« Last post by Gian on August 15, 2025, 11:59:03 AM »

Hi, I did not misplace those components.
I was meticulous in my placement and orientation.

I will swap them for the ones on the other board and see what results I get.