Sound Skulptor forums

Build help and troubleshooting => MU524 Vari-Mu Tube Compressor => Topic started by: Mona on March 21, 2025, 07:50:22 PM

Title: something wrong with my build
Post by: Mona on March 21, 2025, 07:50:22 PM

when I turn Mu524 on my Vac level on the output drops. I can get it right by turning up tr2, but then when I have to match tr 1 and tr2 to  0 volt  I have to turn ytr2 down again and my output level is gone.
I changed the to transistors Q1 and Q2 to be sure they where not the problem but that didn't help.
this are the other voltages. The voltages on the tube sides and v+, v- and b+ are all correct.

A in =  1khz 1.0 vac
tp1 30.6 dc
tp2 30.6 dc
tp1 1.45 vac
tp2 1.45 vac
tp3 1.8
tp4 1.8


 
output 0.141 vac
 
B in = 1khz 0.3 vac
tp3 0.02 vac
tp4 0.25 vac
tp5 0.24 vac
tp6 0.002 vac
 
output 0.5 vac
meter 0

checked everything again can't find any misplacement. Also resoldered the input trafo.
any idea's what I could check else please.

Title: Re: something wrong with my build
Post by: JPK on March 27, 2025, 03:29:59 PM

tp4 1.8
output 0.141 vac

TP4 is good but not the output. It looks like there is a problem on the output stage around U2. Check the solder joints on C12, U2, BR1. Check the direction of U2 and BR1.
Check the signal on U2 pins 1 and 8, in case it is the relay which is defective.
If it doesn't work try replacing U2.

Title: Re: something wrong with my build
Post by: Mona on March 28, 2025, 10:54:35 AM

Thanks,
the signal on pin 1-8 of U2 goes from OL to 9vac. I changed U2 but that didn't help.

Title: Re: something wrong with my build
Post by: JPK on March 28, 2025, 11:05:04 AM

Sorry, I do not understand going from OL to 9vac. Can you explain?

Title: Re: something wrong with my build
Post by: Mona on March 28, 2025, 12:11:36 PM

sorry, wrong measurement.
I measure on U2 pin 1-8 9vac and 15vdc

Title: Re: something wrong with my build
Post by: JPK on March 28, 2025, 05:47:01 PM

Do you measure 15VDC against 0V on both pin1 and pin8 ?

Title: Re: something wrong with my build
Post by: Mona on March 28, 2025, 08:16:52 PM

sorry I'm stupid I measured the wrong pin, 5 instead of 8 so clear that there was 15v. 
the good measure is pin 1-8 0.145 vac no dc.

Title: Re: something wrong with my build
Post by: JPK on March 31, 2025, 07:37:43 PM

Is RLY1 in the correct direction?
Can you measure the signal on U2 pin4? With and without U2 inserted.
Is U2 correctly powered on pins 5(-16V) and 6(+16V)?
Try removing BR1.

Title: Re: something wrong with my build
Post by: Mona on March 31, 2025, 09:01:08 PM

Hi JPK, Rly is in the correct direction. I'm traveling now for 2 weeks, so I can't do the other checks when I'm back and the mu524 is not miraculously working I'll post again. Thanks so far.

Title: Re: something wrong with my build
Post by: Mona on April 19, 2025, 11:37:18 AM

found it. Works like a charm now and sounds amazing. It was a bad soldering at T1 and TR1 was bad. really happy thanks again.

Title: Re: something wrong with my build
Post by: JPK on April 24, 2025, 07:05:50 PM

(https://fonts.gstatic.com/s/e/notoemoji/16.0/1f44d/32.png)