Sound Skulptor forums
Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: morast on August 31, 2026, 01:35:06 PM
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Hi,
i finished my 2nd MP573 build and I'm having troubles getting it to work & would need some advice / guidance.
When the DI board is inserted, JMP3 removed, everything works fine. However, with no DI board, JMP3 on + Mic/Signal via XLR, there is no output.
Tests / measurements I did so far:
DC Values A-K all have the correct voltage.
AC Values with multimeter on 50hz Sine wave via XLR Input:
* In+ to In- : 0,6V
* C2 to C3: 0,6V
* TP2 to T1 Pin 7: 0V
Hints:
* The kit was missing C3, which i then substitutet with a ceramic cap "n47" 100V. (see attached pic).
(https://i.imgur.com/KCCdLVZ.png)
* RLY1 edge got burnt (see attached pic2). I don't remember if it was from soldering iron (unlikely) or due to faulty connection...
(https://i.imgur.com/VHsSI6S.jpeg)
Thanks for you support & cheers from Austria
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The burnt relay is very probably what causes the DI/Mic issue.
You need to replace it.
Mouser/Digikey: TQ2-24V
TME : AZ850-24
Sorry for the missing cap. If you have an other one, you could also replace C2. C2 and C3 must be similar for the best CMRR.
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Hi,
i figured it might be the relais, i'll try to (gently) replace them. ::)
I will replace C2 as well to be of the same type as C3.
Thanks & kind regards,
Herbert
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Hi,
i swapped the relay which is working now, however, i fucked up the input trafo in the process :o.
I'll send you an email / pm because now i need spare parts, haha.
Cheers,
Herbert
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Too bad !