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MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by JPK on May 08, 2026, 08:46:01 AM »

Can you tell me which pins were shorted?
What results do you get from the voltages checks in the test guide steps 2 to 5?

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MP566-II Tube microphone preamplifier with HPF / Possible ICs fried MP566-II

« Last post by spurton@gmail.com on May 07, 2026, 09:10:04 PM »

I recently built the MP566-II Tube pre and when I first powered it on I could not get any sound out of it. So I removed it and discovered I had a solder bridge on the back of the header pins to the tube PCB. I fixed the bridge and ran it again. It puts out sound but very quiet, not enough to register signal but I can hear it faintly. It also distorts heavily when I turn up the gain knob or output knob. I know shorting leads can fry the ICs. Does this sound like what I did? If so I will order new ones. Thank you. 

3

Discussions about the products / Re: LA502T Tube Compressor Setup

« Last post by UrbanOsterman on May 01, 2026, 10:23:48 AM »

Thanks,
Later I looked closer and then I realised it was The SKTPS that was meant.

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Discussions about the products / Re: LA502T Tube Compressor Setup

« Last post by JPK on April 30, 2026, 07:58:00 PM »

Sorry for the mistake, it is not U5 but U9, the large préassembled module.

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Discussions about the products / LA502T Tube Compressor Setup

« Last post by UrbanOsterman on April 30, 2026, 05:05:24 PM »

I have just finnished building the LA502T Compressor.
And I am trying to set it up.
But I dont understand 
point 3 Section 'High voltage check' and 'Heater voltage check'

High Voltage check:
  It says I should check the voltage Between V- an B+ pin on U5 
  (which is a TL431 chip).
  the Setup paper say it will start at 30V and rise up to about +225V.
  But I measure just 2,48V?

And in section
Heater voltage check 
it says  I shuld meassuer between H- and H+ on U5 (same TL431) ... it should go from 7 Volt up to 12 Volt.

I assume some thing is very strange here?

Urban Osterman

 

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MU524 Vari-Mu Tube Compressor / pair of MU524 - crackling/noise/hiss

« Last post by herwig.scheck on April 30, 2026, 11:37:30 AM »

Hi,

I have a pair of MU524's. One has a cracklinkg/noise/hissing problem. When I turn down the gain (in as well as out) the noise goes down with it. After some swapping out of the tube and op-amps between the units the problem stayed. 

Until I swapped out the U6. They're different for both units and the problem moved with the U6. The "small" one behaves while the "tall" one is the noisy one.
When I touch/tap the small daughter board I can hear that in the circuit.


Is there something I can do on my end or should I contact support for this?


TIA,
Herwig

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

« Last post by JPK on April 29, 2026, 09:13:34 AM »

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

« Last post by Ben on April 29, 2026, 05:29:16 AM »

I found it at last! there was a tiny solder bridge between pins 3 and 4 on U2. Thank you so much for your help and patience?
Cheers!
-Ben

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

« Last post by JPK on April 28, 2026, 09:07:39 AM »

7  0.05vdc
This should be 0.00VDC.
Maybe something prevents the output from changing.
Check that there is not a short circuit between TP4 (output of U1.2) and 0V or an other point around J1-pin17-18, C12, C9, R15.

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

« Last post by Ben on April 28, 2026, 12:33:29 AM »

I have 1.65vac at pin 5 of U1, voltage doesn't seem to get to pin 7, I have tested R15, R16, C9, C10, C11 multiple times and all appear good and the traces all seen ot have the correct continuity with the components.  I've also swapped the op amps and get the same result.