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MU524 Vari-Mu Tube Compressor / Re: MU524 is noisy

« Last post by egelmett on Today at 06:59:11 PM »

Check if any component is overheating, U2 in particular.

How does one know if U2 is overheating? Is this estimated by touch, or measured in some manner?

OttoWei's discription, and troubleshooting is the exact same issue as mine...I had to double-check it wasn't me who wrote the initial post! 

Ed

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SK49 Multi-patern Tube Microphone / Re: How long is the 7-pin XLR cable that comes with the SK49 kit?

« Last post by Alex Harmer on Today at 12:50:59 PM »

I think the best method would be to check the voltage across R13 in the PSU.
You want around 140mA in the tube heater so the voltage should be about 0.14 * 27 = 3.78V.
If the current falls under 133mA (3.6V accross R13) you can lower the value of R13 to increase the current.

Hi JPK,

I'm resurrecting this topic about the 25-metre long 7-pin cable for orchestral recording. 

Would you consider selling me two new power supplies with a specific value in R7 that would be appropriate for the voltage drop across this length of cable? 

The microphones are amazing - and rather than risk damaging the power supplies with some modifications that I don't understand, I'd prefer to have two dedicated power supplies for when I am using longer cables. 

What do you think? The microphones are amazing, and I'd like to use them for this task of longer cable runs. 

Cheers from New Zealand. 

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MP573 Microphone preamplifier / Re: Second hand MP573 with -6dB level drop

« Last post by JPK on Today at 11:29:51 AM »

Perform the checks described here, starting by Try to follow the signal:
https://www.soundskulptor.com/forum/index.php?topic=5.msg5#msg5

Report any difference.

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MP573 Microphone preamplifier / Re: Second hand MP573 with -6dB level drop

« Last post by sdiazmun on Today at 10:16:03 AM »

Yes, at all gain and output positions

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MP573 Microphone preamplifier / Re: Second hand MP573 with -6dB level drop

« Last post by JPK on Today at 09:59:19 AM »

Is the 6dB drop the same for a gain set to 20dB and a gain set to 30dB ?

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MP573 Microphone preamplifier / Second hand MP573 with -6dB level drop

« Last post by sdiazmun on April 20, 2026, 08:07:07 PM »

Hi!!

Im just received a second hand MP573 (I have other three), and after compare them with "Smaart", the last one has a -6dB drop across the entire frequency spectrum, and that difference remains even when modifying the gain or the output potentiometer.

Where should I start looking for the point of failure?

Thanks in advance
Regards 
Sergio

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

« Last post by JPK on April 20, 2026, 11:19:16 AM »

Now I lost ac voltage at TP1 and I still get 1.64vac at TP3 and 0.055vac at TP4
You can debug without the front panel PCB connected. This will help to narrow down the search area.

Just to confirm
Normal. 2 pins are connected together. 10kohms max between the 2 other pins.

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on April 20, 2026, 11:09:08 AM »

Contact me here for a repair.

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

« Last post by Ben on April 18, 2026, 11:01:38 PM »

I'm stumped, Now I lost ac voltage at TP1 and I still get 1.64vac at TP3 and 0.055vac at TP4
I still have 30vdc at TP1 and 2 as well.
Just to confirm, what value should I be getting on P1? the impedance stays at 0 when turning the pot on the right 2 pins when looking at the pot from the rear, It varies between 0 and 10k on the left 2, I get 10k on th outer 2 pins

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on April 18, 2026, 04:57:30 AM »

Well I think if there’s nothing left to check, I give up.  I’ve replaced Q7 three times and still am coming up with the same results.  I’ve looked over the schematic and retraced everywhere for continuity.  Every part I’ve pulled out has tested fine.  All of the Q7 transistors have tested identical out of circuit.  I haven’t had trouble like this with other diy kits so I’m feeling a little defeated.  There must be something small I’m overlooking somewhere.