41

MU524 Vari-Mu Tube Compressor / Re: test step 6 voltage

« Last post by JPK on May 26, 2025, 03:20:05 PM »

22.7 V semble peu vraisemblable. Il y a peut-être un Pb avec le voltmètre. Vérifiez la pile ?

42

EQ573 Equaliser / Re: Knob issue

« Last post by JPK on May 26, 2025, 03:11:23 PM »

You may have overtightened the screw on the red knob. You need to tighten it very gently.

43

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

« Last post by JPK on May 26, 2025, 03:09:00 PM »

2mV of noise at the output is normal with IN and OUT pots at max. 14mV seems a lot.
All tubes are more or less microphonic, this also is normal. Taping on the tube can create an output voltage of 50-60 mV.

44

MU524 Vari-Mu Tube Compressor / test step 6 voltage

« Last post by PMswing on May 26, 2025, 11:04:22 AM »

Bonjour, je suis à l'étape 6 de test du MU524, ma tension entre les pins 2 et 4 du XT500 avec le potentiomètre out à 0 est de 2,7V (contre 3 et 4 demandé) et avec le pot à fond j'obtiens 22,7 V (contre 9V ou plus demandé) , Qu'en pensez vous ? Merci d'avance.

45

EQ573 Equaliser / Knob issue

« Last post by MRMNW on May 24, 2025, 11:13:38 AM »

Hi
I’m having an issue where the frequency dial often moves the gain knob with it, is there any way to avoid this? Is this normal behaviour? 
Thanks

46

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

« Last post by seanlew98 on May 23, 2025, 10:18:34 PM »

Tho one thing I was wondering about before, I think I might have a microphonic tube.

Did some testing with my 12ax7 tube in for comparison. I did however noticed after the fact that the 12ax7 isn't glowing while the ECC189 was. The levels on the 12AX7 are more akin to the "soft" start mode before I bridged the resistor too.

What do you think? Is it still just noise from my rack since it's so "microphonic"?

https://drive.google.com/drive/folders/1EvaXznCp-66F9AlMgMM0UjU_vV91IWNP?usp=drive_link

EDIT: PS* Also from some searching I've understood that a "microphonic tube" isn't really what it is, the tube seems okay but is it normal for it to pick up so much noise around it? Just wanting to see if it's the source of the hiss.

Just measured the noise level with output knob all the way up and it's around 0.014VAC. I am however using a Midas L-10 tho, getting the link audio X-10 mod for it with the high end external PSU. Would report back on whether noise levels improve.

Thanks!

47

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

« Last post by seanlew98 on May 23, 2025, 09:51:38 AM »

It is indeed reversed. Lemme fix that real quick!

Flipped Q4 back and removed the bridge wire on R39 and it's working! You're a wizard man!!

48

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

« Last post by JPK on May 23, 2025, 09:43:37 AM »

It would be preferable to repair the soft start to extend the tube life.
I am not 100% sure but from your picture, I suspect Q4 being reversed. The writings on the transistor but be facing towards R38. Please check.

49

MU524 Vari-Mu Tube Compressor / Re: Hissing Noise on Output only - Voltage Regulator?

« Last post by seanlew98 on May 23, 2025, 08:01:06 AM »

Mouser is actually really close to my house so I’ll just grab that one. Obviously it looks different but I’m assuming the same function as the one provided in the kit? Any differences in sound expected between the too? Being a voltage regulator I assume not.

Im fairly certain last time I had the unit open C9 was fine. I’ll double check it again though when I install the voltage regulator.

Hi did this help?

50

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

« Last post by seanlew98 on May 21, 2025, 08:56:59 PM »

OMG Tube's glowing for the first time ever!

Step 4 Voltage is @ 6.19 VDC.

Do I leave the wire in? What's next? Didn't leave it powered on for long just in case.

EDIT:

I calibrated it and each step was right in the Trip pot range with no difficulties.

One thing tho, there seems to be a hiss coming from the output knob, I've seen it reported before as well. Any remedy for that?