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MU524 Vari-Mu Tube Compressor / manque JmP1 et ref transistor

« Last post by PMswing on May 10, 2025, 04:43:05 PM »

Bonjour,

je suis entrain de monter le MU524 et je n'ai pas d'embase JMP1 3 broches par contre j'ai une embase 2 broches qui ne correspond à rien. Que faire s'il vous plait ?

Par ailleurs, et juste pour être sur, les deux transistors Q1 et Q2 n'étaient pas les même references (un noté CEN.MPS.A29 et l'autre JCMP.SA29.R19) ils sont les même ? peu importe leur emplacement ?

Merci,

Pierre

62

MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by greyskull on May 07, 2025, 07:17:30 PM »

Thanks JP.

Unit is passing audio and output is up to 14.1V when out Is Maxed.

I've checked continuity between legs of tube and board to be sure, so I Think you're right!
I'll be in touch Via form/Email. Thanks again.


Guy

63

MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by JPK on May 06, 2025, 04:36:25 PM »

TP3 = TP4 = 0 VAC
Were you able to get 9VAC in step 6?
If true, then you may have a defective tube. Contact me here for a replacement.

64

MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by greyskull on May 05, 2025, 06:52:23 PM »

Thanks for getting back so fast JP.

I've re-flowed all of those and am getting the same readings with U4 pulled out of circuit and still not able to adjust balance to 0.


TP1 = 34.8 VDC (black probe on 0V)
TP2 = 40.7 VDC (black probe on 0V)

TP1 = TP2 = 0.82 VAC
TP3 = TP4 = 0 VAC


Picture attached in case I've done something stupid.
Many thanks again

65

MP573 Microphone preamplifier / Re: Laster Version of the Assembly Docs, Docs-24

« Last post by musicarr on May 05, 2025, 02:34:01 PM »

Thanks very much for the confirmation. I'll get started building.

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MP573 Microphone preamplifier / Re: Laster Version of the Assembly Docs, Docs-24

« Last post by JPK on May 05, 2025, 09:30:44 AM »

DOCS-20 is the correct documentation. The changes between DOCS-20 and DOCS-24 affect other products.

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MU524 Vari-Mu Tube Compressor / Re: MU 524 Stuck on Step 7

« Last post by JPK on May 05, 2025, 09:28:13 AM »

Check the solder joints on R6, R7, R9, R10, Q1, Q2.
Check that TR2 is working properly: Resistance going from 0 to 1k between center pin and one side pin and goinf from 1k to 0 on the other side pin.
Check again the balance setting after removing U4.

68

MP573 Microphone preamplifier / Re: Laster Version of the Assembly Docs, Docs-24

« Last post by musicarr on May 04, 2025, 11:20:25 PM »

In looking at the DOCS on the product page a little closer, it says, "from DOCS-20". The previous versions of DOCS suggest ranges, i.e. "from DOCS-13 to DOCS-19". Is it safe to assume that "from DOCS-20" is the correct assembly instructions from DOCS-20 through all others after that ?

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MP573 Microphone preamplifier / Laster Version of the Assembly Docs, Docs-24

« Last post by musicarr on May 04, 2025, 01:52:49 AM »

Hi,

Was about ready to start my build. On the outside of the box, is says, "DOCS-24". I'm presuming that's the current exact docs version I need for this version of the kit I have. But on the product page, it only goes up to "DOCS-20". Where can I find "DOCS-24"?

Thanks.

70

MU524 Vari-Mu Tube Compressor / MU 524 Stuck on Step 7

« Last post by greyskull on May 03, 2025, 04:35:31 PM »

Hi there, I've just finished putting this together, and I can't get the balance to read 0 Volts between tp1 and tp2. It only goes down to 5.9 volts before the trim pot hits the end of its travel. I've stopped at this point before breaking anything!

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 = 34.8 VDC (black probe on 0V)
TP2 = 40.7 VDC (black probe on 0V)

TP1 = TP2 = 0.82 VAC
TP3 = TP4 = 0 VAC
Output: 1.12 VAC (between XLR pins 2&3)