1

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: February 10, 2024, 03:19:35 PM »

Yep, seems like C12 was touching one of the pins on the transformer board, I yanked it apart, also the tube board and got it working now. Thank you very much for the help.
I just was able to check it on a bass track and really like what it does, will probably get a second one soon to try in on the drum buss.
Cheers,
Jakov

2

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: February 03, 2024, 12:12:51 PM »

nitial conditions:
IN pot @ max
OUT pot @ min
REC pot @ max
Bypass toggle @IN
All Push buttons @UP
Input signal: Sinus 1kHz, 1VAC
Jumper JMP1: removed

Results:
TP1 = 36,94 VDC
TP2= 38,20 VDC 

TP1 = 12,58 VAC
TP2 = 6,46VAC
TP3 = 5,66 VAC
TP4 = 5,47 VAC
Output: 10,51 VAC (between XLR pins 2&3)

3

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: February 03, 2024, 11:59:11 AM »

The usual suspects look OK.
The measured voltages:

Test step 4: DC voltage between two side pins: 6,0629 VDC

Test step 5:
V+=15,378
V-=-15,212
B+=46,012

Test step 6:
Sine 1 KhZ
in bypass voltage on output pins 2-3 =1.0007 VAC
comp on voltage on output pins 2-3 =10,517 VAC

When I remove the input signal, the voltage drops to 6,204 VAC and the multimeter shows 0,230 kHz

 

4

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: January 20, 2024, 10:52:21 AM »

Very similar problem like the previous user, initial checks are OK,, V+, V-, B+ voltages OK. When I apply the 1VAC 1kHZ sine and engage the the voltage measures far to high approx 10,85 VAC and increase P2 it grows up 17,49 20 VAC.
I already checked R1, R2, they should be OK and are not touching the out- transformer pins. When I remove the ICs and measure between pins 6-7 of U1 I measure 0,6 Ohm to 2k2.

Disassembled everything mechanically and put again together (tube, ICs, PCBs..) several times with the fault is persistent.

help appreciated...