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MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« Last post by aj99009 on July 02, 2024, 08:13:28 PM »

Found the problem.
I had R8 and R18 in the wrong spots..  Switched them and everything is working good now!
Rookie mistake..

Thank you for helping me figure it out!

2

MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« Last post by JPK on July 02, 2024, 03:39:20 PM »

The upper side of R8 should be at 46 Volts.
It is only connected to R6, R7 and C7.
Check these components. There must be something wrong here, like a solder bridge of a bad solder joint.

3

MP573 Microphone preamplifier / Re: Bias Adjust

« Last post by JPK on July 02, 2024, 03:30:21 PM »

I ususally wait 5 mn before adjusting.

4

MP573 Microphone preamplifier / Re: Bias Adjust

« Last post by Evan Sabby on July 01, 2024, 09:11:49 PM »

Thanks.  Should I wait for the voltage to settle before I adjust P2 to 3 volts or will it be ok the way I adjusted it right after I powered the unit on?

5

MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« Last post by aj99009 on July 01, 2024, 04:40:16 PM »

Ok so tested 0v to both sides of R8.

Lower side of R8 (toward the TP pins) reads 46.6
Upper side of R8 reads .607

6

MP573 Microphone preamplifier / Re: Bias Adjust

« Last post by JPK on July 01, 2024, 03:20:56 PM »

It is normal for the voltage to drop a little, around 100mV, as the unit warms up but it should stop when it reaches its equilibrium temperature.

7

MP573 Microphone preamplifier / Bias Adjust

« Last post by Evan Sabby on July 01, 2024, 12:57:10 AM »

I have a question about the bias adjust portion of the testing.

I place the positive (+) test probe from the DMM on TP4 and the negative (-) test probe from the DMM on TP2.  I power on the unit and adjust P2 until I read 3 volts.  My question is after I get P2 adjusted to 3 volts the voltage begins to drop very slowly and continues to drop over time.  Is this ok?  If not what do I need to do to fix it?

I appreciate any input.

Thanks,

Evan

8

LA502 Optical Compressor / Re: LA502 - PCB 1.2->1.3 C5 47p cap

« Last post by JPK on June 27, 2024, 05:53:11 PM »

No, not necessary.
This cap ensures better Common Mode Rejection Ratio (CMRR) in case the 2 caps differ in value.

9

LA502 Optical Compressor / LA502 - PCB 1.2->1.3 C5 47p cap

« Last post by rameau on June 25, 2024, 12:53:18 PM »

Hello,

I bought the LA502 PCB 1.2-Version and already did the mod for reducing noise.
In addition to that mod, there is an additional C5 47p cap at the input part of PCB 1.3 who's been missing in PCB 1.2.
Is it also recommed to add this C5 cap?
What exactly is the benefit of this cap in addition to the two 470p caps?

thanks!
best regards,
Guido

10

MU524 Vari-Mu Tube Compressor / Re: AudioPath Test Question

« Last post by JPK on June 23, 2024, 03:36:56 PM »

What is the DC voltage on each side of R8, against 0V ?