51

MU524 Vari-Mu Tube Compressor / Re: MU524 Low Tube PCB Voltage

« Last post by seanlew98 on May 21, 2025, 08:35:29 PM »

shorting as in connect both leads of of R39? Will try in a bit!

52

MU524 Vari-Mu Tube Compressor / Re: MU524 Low Tube PCB Voltage

« Last post by JPK on May 21, 2025, 04:52:10 PM »

It looks like the soft start of the tube heater always remains on "soft".
Try shorting R39 (18R) with a little piece of wire and check if the tube heater voltage (step 4) looks better.

53

MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by JPK on May 21, 2025, 03:56:29 PM »

BUT in Step 8, TR 1 doesn't seem to affect anything.
Check That TR1 is working : 0 to 1k3 (approximately, in circuit).
Check the solder joints of R3, R4.
Where you able to do the sub-steps of step 8, before TR1 adjust?
How many DC Volts did you get on TP6 and on U4-pin6 (against 0V), when you did this:
?  Adjust TR4 (Vref) until you read 3.0VAC.

In all cases, we can fix it for you, contact me here.

54

MU524 Vari-Mu Tube Compressor / Re: MU524 Low Tube PCB Voltage

« Last post by seanlew98 on May 21, 2025, 12:24:21 PM »

*update*

Reflowed practically everything one leg at a time on IC and transistors to not overheat, and exactly the same, 2.54 VDC on the two outer legs of tube PCB, no glow.

55

MU524 Vari-Mu Tube Compressor / MU524 Low Tube PCB Voltage

« Last post by seanlew98 on May 21, 2025, 07:18:49 AM »

Hi all, I've a problem with my MU524, the voltages didn't seem quite right upon first step of setup but I went through with the calibration anyways just in case. The compressor is working and might I say sounds pretty damn good, but I feel something is still not right given that I couldn't get the setup parameters right and it's also a lil low on the output.

Lemme run you through the details.

SETUP

Outer pins of tube PCB would only go up to 2.486 VDC MAX, even after half an hour.

Tube doesn't glow at all, same tube glows in my orange micro terror amp. Tube gets barely warm after a long time being powered on, it's basically as warm as the output transformer and the Q4 U U6 area.
Swapped 12AX7 tube from amp into MU524, voltage got up to around 4.45VDC but nowhere near 6v even after long. Swapped back to stock tube for rest of test.

V+ 15.72 VDC

V- -15.69 VDC

B+ 45.28 VDC

1.0 VAC Sine tone bypass, when compressor is in it drops to 0.523 VAC (!!!)

output pot maxed out reads only 5.927 VAC

rest of the setup was okay except for step 10 TR5 Couldn't hit 3.0 VAC, was about 2.43 VAC

Also scrubbed through some other similar posts and measured:
- 6.19 VDC between V- test pin and the right side pin of the tube holder PCB (marked H).
- Q4 is warm
- C32, C33 not reversed

Troubleshooting:

TPI
43.57 VDC
0.232VAC

TP2
43.97 VDC
0.124 VAC

TP3 = TP4
0.244 VAC

output 0.489 VAC

changed conditions

TP3
0.09 VAC

TP4
1.058 VAC

TP5
1.037 VAC

TP6
-0.773 VDC

Output 2.1 VAC

GR Meter 1.5dB

Here are some pics for reference!
And yes, followed the steps in detail for both calibration and troubleshooting, including knobs & switches positions & removing and attaching of JMP1.

Also, I had to desolder the two headers on the meter PCB (J1B & J2B) cause I soldered em on the wrong side (yikes). They're resoldered on fine with some pins coming out but reposition levelled with the rest, and the pots & switches were fully working in the final assembly so I don't think that would be the issue. Also since the power side (?) isn't on this PCB.

Also, bit of an embarrassing thing, when I got to the relay step on the build guide, I thought IC's was similar having soldered IC's in previous builds so I just soldered them in and only say the IC sockets later on. Could that be the problem? Seemed unlikely to me since I have fully functioning and great sounding compression.

Please help

56

MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by greyskull on May 19, 2025, 10:34:24 PM »

Hi JP,
Either I'm extremely unlucky or very stupid.
With the new Tube I was just about able to get the voltage down to 0 between tp 1 and 2 in step 7
BUT in Step 8, TR 1 doesn't seem to affect anything.
Similarly, adjusting TR5 further down, has no affect.

Could it be I've had two tubes each with one half bad? In any case should I send the unit in at this point to prevent you being further out of pocket?

I followed the rest of the instructions to the end, and whilst I wasn't able to calibrate the unit within spec, it works, in so far as it passes audio and compresses, albeit with an increased noise floor as you turn the attack - which would lead me to think that the tube halves are not balanced.

Any help gratefully received.

Many thanks.
Guy

57

MU524 Vari-Mu Tube Compressor / Re: manque JmP1 et ref transistor

« Last post by JPK on May 12, 2025, 09:56:12 AM »

En effet, le document n'est pas  à jour, nous corrigeons immédiatement !

58

MU524 Vari-Mu Tube Compressor / Re: manque JmP1 et ref transistor

« Last post by PMswing on May 11, 2025, 05:51:44 PM »

Merci pour votre réponse, le document est le "MU524 parts list" fourni avec le kit, je vous envoie la photo par mail.

59

MU524 Vari-Mu Tube Compressor / Re: manque JmP1 et ref transistor

« Last post by JPK on May 11, 2025, 03:43:10 PM »

Embase 2 broches : Désolé c'est une erreur, on vous envoie ça demain.
Les transistors sont identiques, pase de problème.
Le pot 202 et le bon. Sur quel document avez-vous vu 203 ?

60

MU524 Vari-Mu Tube Compressor / Re: manque JmP1 et ref transistor

« Last post by PMswing on May 10, 2025, 06:43:13 PM »

J'ai aussi un potentiomètre ajustable tr1 noté 202 au lieu de 203 dans la nomenclature, c'est bon ?