1

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: October 14, 2023, 08:03:29 PM »

Sorry, yes P2.
It seem P2 does not go down to 0 Ohm.
Can you check directly on the pot, between the center pin and each side pin, after disconnecting the front PCB?

- I think my nomenclature was a little unclear in my last post. It went down to 300 milliohms, or .3 ohms, so I think it was functioning okay.

- I built by second of my stereo pair and it passed all tests perfectly. After some more troubleshooting swapping out ICs and the tubes between the two units, the first unit started operating normally, so I guess something may have needed to be re-seated. So everything is great now! Thanks so much for your time in helping me troubleshoot - and thanks for making great products =)

2

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: October 12, 2023, 05:53:34 PM »

These values are good.
With power off and still no IC's, measure the minimum resistance value of P1 between pins 6 and 7 of U1. It should go from 0 to 2k2.

Did you mean to say P2? P2 measures from 2.075k ohms to 300m ohms across pins 6 and 7 of U1

3

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: October 12, 2023, 08:46:07 AM »

Check values of R1, R2 and P1.
In step 3 initial conditions,
Do you hear the pure input tone at the output or is it hum or noise?
What are the AC and DC voltages you get on TP1 & TP2?

- Values of R1, R2 and P1 are correct

- I hear pure tone at step 3

With no front PCB and no ICs, 1VAC sine wave applied I get:

TP1: 1.66VAC, 30.42VDC
TP2: 1.75 VAC, 30.41VDC

4

MU524 Vari-Mu Tube Compressor / Re: MU 524

« on: October 12, 2023, 07:31:40 AM »

Hey I'm having a similar issue with my MU524: getting an unusually high output for step 6 of the setup guide (about 5.6 VAC from the output with initial conditions). When I turn the output knob up, it goes up to 22VAC.

Input transformer label is facing the back, and I feel as though I've done a good job double checking component placement and values.

With no front PCB and with all ICs removed, I get exactly 3VAC across TP3 and 0V.