Sound Skulptor forums

Build help and troubleshooting => MU524 Vari-Mu Tube Compressor => Topic started by: b.riesel on March 09, 2023, 08:58:07 PM

Title: Problems with my build
Post by: b.riesel on March 09, 2023, 08:58:07 PM

Hi Jean-Pierre

I have problems with my build of the Mu524.
I did the setup, step by step. 
I got to point 9 "sidechain setup" during setup. 
Up until then everything was fine. At point 9, I could only get TR3 down to 4.8 VAC. Nothing went deeper.
Nevertheless, I completed the setup process and all the rest of the values were correct, except for TR3.

After that I checked the values from your post „In case your MU524 doesn't work as expected (https://www.soundskulptor.com/forum/index.php?topic=347.msg1907#msg1907)“.
Here are the results:

Initial conditions:
IN pot @ max
OUT pot @ min
REC pot @ max
Bypass toggle @IN
All Push buttons @UP
Input signal: Sinus 1kHz, 1VAC
Jumper JMP1: removed

Results:
TP1 and TP2: 30VDC (black probe on 0V) TP1 15,6 VDC, TP2 34,2 VDC
TP1 and TP2: 1.25VAC  TP1 - Ground 1,99 VAC, TP2 - Ground 0L to 38 VAC jump around, couldn’t get a result from the measurement
TP3 = TP4 = 1.8VAC TP3 - Ground 3,5 VAC, TP4 - Ground 3,49 VAC
Output: 3.5VAC (between XLR pins 2&3) 3,4 VAC

Changed conditions:
Jumper JMP1: on 1-2
Input signal: Sinus 1kHz, 0.3VAC
OUT pot @ max

Results:
TP3: 0.26VAC (black probe on 0V) TP1 - Ground 0,23 VAC
TP4: 1.5VAC TP4 - Ground 2,6 VAC
TP5: 2.9VAC TP5 - Ground 2,55 VAC
TP6: -3.5VDC TP6 - Ground -3,23 VDC
Output: 3.5VAC (between XLR pins 2&3) 2,67 VAC
Meter: -6dB -6dB


When I send a musical Signal in the unit, I get heavy plops , the frequency of the plops is getting lower, the higher recovery time gets.
As far as I rise the input, the gain reduction is immense, the input signal seems far to loud.

Do you have an Idea what could be wrong?

Best regards and a thousand thanks for your support.
Stefan

Title: Re: Problems with my build
Post by: b.riesel on March 13, 2023, 04:25:46 PM

Hi Jean-Pierre

I just want to correct that with the plop noises. If I increase the recovery time, the repetition frequency of the pop noise decreases. Not the frequency of the noise itself.

I hope, you´ll have an idea, what could be wrong.

Best regards
Stefan

Title: Re: Problems with my build
Post by: JPK on March 15, 2023, 11:20:21 AM

TP1 and TP2: 30VDC (black probe on 0V) TP1 15,6 VDC, TP2 34,2 VDC

Something wrong in the tube stage. Check the value and solder joints of TR1, TR2, R3 to R7, tube socket and tube PCB connectors.
When TR2 is properly set, the DC voltage on TP1 and TP2 should be the same.

Title: Re: Problems with my build
Post by: b.riesel on March 15, 2023, 06:25:21 PM

Hi Jean-Pierre
Ich checke everything and resolderd some elements, but everything looks fine.
So I did the setup again an got the following result:

Power-Voltage check:
V+ to 0V = +15,4 DCV
V- to 0V = -15,5 DCV
B+ to 0V = 45,5 DCV

Audio path check:

Signalamplitude 1,0 VAC in bypass
now, when I switch the compressor "in", I got 7,3 VAC.
When I turn the Out knob, it increases up to 13,2 VAC

Tube balance 1:
TR2 minimum was -17,36 DCV

Tube balance 2:
I did the trim on TR3,4,5 and set the jumper to 2-3
I adjusted the Out pot to get 6,0 VAC
I adjusted TR4 but could only get 2,0 VAC

Then I started again from the beginning.

Audio path check:

Signalamplitude 1,0 VAC in bypass

now, when I switch the compressor "in", I got only 0,3 VAC.
When I turn the Out knob, it increases up to 1,56 VAC

after 10 more minutes I get 0,47 VAC and can increase up to 1,74 VAC.

do you have an idea, what's wrong?
best regards
Stefan

Title: Re: Problems with my build
Post by: JPK on March 16, 2023, 11:02:11 AM

Tube balance 1:
TR2 minimum was -17,36 DCV
To set tube balance 1, the voltmeter must be placed between TP1 and TP2 and TR2 must be adjusted to get a voltage as close to 0V as possible.

Title: Re: Problems with my build
Post by: b.riesel on March 16, 2023, 01:10:41 PM

isn´t it an issue, that while audio path check, i first got 7,3 VAC, when switching "in", and only 0,3VAC in my second run?
Or does this depend on the trim of TR2?

Best regards and thank you so much for your help.
Stefan

Title: Re: Problems with my build
Post by: JPK on March 16, 2023, 04:05:22 PM

You are correct, this is an issue.
Check again the power voltages (setup guide step 7).
If OK, check that you receive the input signal between pins 7 & 10 of the input transformer: 0.65VAC with IN pot @max.
And 0.27VAC between pins 2 & 5.
And 1.8VAC (+/-20%) on TP3.

Title: Re: Problems with my build
Post by: b.riesel on March 16, 2023, 06:27:57 PM

Hi Jean-Pierre

here are my results:



Audio path check:

Signalamplitude 1,01 VAC in bypass

when I switch the compressor "in", I got only 0,4 VAC.

When I turn the Out knob, it increases up to 1,7 VAC




You are correct, this is an issue.
Check again the power voltages (setup guide step 7).
If OK, check that you receive the input signal between pins 7 & 10 of the input transformer: 0.65VAC with IN pot @max. 0,67VAC
And 0.27VAC between pins 2 & 5. 1,18VAC
And 1.8VAC (+/-20%) on TP3. I don’t understand, how to measure TP3, sorry...0V to TP3 = 0VAC?

Title: Re: Problems with my build
Post by: b.riesel on March 20, 2023, 08:35:56 AM

Hi Jean Pierre
Unfortunately, I have absolutely no idea how to narrow down the error further. I can't see any error visually. I posted my test results. Unfortunately, I am quite ignorant and have no idea how to get the device to work.
I would be very grateful for a tip.
Best regards
Stefan

Title: Re: Problems with my build
Post by: JPK on March 20, 2023, 09:36:00 AM

Remove U3 & U4 in order to test the audio path alone, without interaction from the side chain.

And 0.27VAC between pins 2 & 5. 1,18VAC
Does it return to 0VAC when you remove the input signal?

I don’t understand, how to measure TP3, sorry...0V to TP3 = 0VAC?
DMM red probe on TP3, black probe on 0V.

have no idea how to get the device to work.
If you would like us to repair your unit, contact us here (https://www.soundskulptor.com/en/content/6-contact).

Title: Re: Problems with my build
Post by: b.riesel on March 20, 2023, 07:35:14 PM

Hi Jean-Pierre

I did the Measurement with removed U3/4




Remove U3 & U4 in order to test the audio path alone, without interaction from the side chain.

And 0.27VAC between pins 2 & 5. 1,04VAC
Does it return to 0VAC when you remove the input signal? No, it goes to 1,02VAC and

These are the same values as with U3 and U4.

DMM red probe on TP3, black probe on 0V.
this is 0VAC

I noticed one more thing. I can only hear the test tone when the module is switched off. 
As soon as I turn on the compressor, the sound goes away, even if I turn on the out. Does that help in any way? What does that mean?

Best Regards and thank you so much for your patience.

Stefan

Title: Re: Problems with my build
Post by: JPK on March 21, 2023, 08:58:16 AM

Please check the usual suspects (https://www.soundskulptor.com/forum/index.php?topic=347.msg1907#msg1907), in particular the last one.
If nothing works, maybe it is time to send us the unit for a check. Contact us here (https://www.soundskulptor.com/en/content/6-contact).

Title: Re: Problems with my build
Post by: b.riesel on March 21, 2023, 10:21:20 AM

OK, I'll check it again carefully and if I shouldn't be successful again, I'll get in touch with you to send it in. Thanks in advance.

Regards, Stefan