1

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: July 04, 2023, 12:17:26 PM »

Yes, it was the pot! It's working just fine now...thanks you very much for the great help!!!

2

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: June 21, 2023, 11:07:18 AM »

Without front PCB and IC's TP3 = 2,3Vac

3

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: June 20, 2023, 10:18:06 AM »

The initial condition measures (without the front PCB) are:

TP1-0V = 29,6Vdc
TP2-0V = 29,4Vdc

TP1=TP2 = 3,4Vac

TP3=TP4 = 0,01Vac

Output = 1Vac

I resolder every pot joint and the connectors between the PCB's. The output voltage still changes, wen I press against the front PCB. I have ordered new input and output pots. maybe this will fix it. 
I have checked all the 5x2 and 10x2 connections between the PCB's with an DMM and most of the connection pairs on the 10x2 connector are linked. Is that right? 

4

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: June 19, 2023, 11:11:07 AM »

Could be something wrong with pot 1 (Input pot). When I measure the output voltage it jumps between 2-26V when I press the input pot a little to the side. Do you have an idea what could be the problem there?

5

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: June 19, 2023, 10:38:48 AM »

TP3 to 0V = 0Vdc
TP4 to 0V = 8,2mVdc

6

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: June 16, 2023, 12:36:39 PM »

Thank you for the response! 

The input transformer label is facing to the back and the Torx screws are on the correct spot upwards. 
I resolder every joint and checked the components (except the small ceramic capacitors, they are to small to read). Everything seems fine.

When I check the voltages I get: 

Initial 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 = TP2 = 29.3VDC (black probe on 0V)
TP1 = TP2 = 2.4VAC
TP3 = TP4 = 13.8VAC
Output: 26.5VAC (between XLR pins 2&3)

Changed conditions:
Jumper JMP1: on 1-2
Input signal: Sinus 1kHz, 0.3VAC
OUT pot @ max

Results:
TP3: 0.21VAC (black probe on 0V)
TP4: 8.24AC
TP5: 2.32VAC
TP6: -2.77VDC
Output: 16.4VAC (between XLR pins 2&3)

7

MU524 Vari-Mu Tube Compressor / MU 524

« on: June 14, 2023, 06:22:05 PM »

Hello,
I just build two MU524. The first one is working and I had no problems with calibrating the unit . 
But the second one has over 26Vac at the Output in Step 6, were it only should have 3-4Vac. In Bypass it is the normal 1Vac at the Output. As soon as I engage the the bypass to „In“ its 26V. I checked the pots and could‘t find and mistakes. Do you have and thoughts? 

V+ and V- are +- 15-16V 
B+ is 46V
TP1 = 30V
TP2 = 27V but maybe its because I didn’t end the calibration. 

Best regards! 
Benjamin