1

LA502 Optical Compressor / R5 100K reads 26.6K after soldering it in... correct? DOC24

« Last post by noeqplease on Today at 07:09:26 AM »

Hi all,

I am populating my first 502 compressor, and on one resistor, R5, which is 100K, after soldering it in, it reads 26.6K.

This is on DOC24, the version I am building.

Is this a normal reading for that? I know sometimes you can get mixed or different readings when things start getting connected around the circuit.

Thanks!

2

First Aid / Re: True Grit (Kit) not working

« Last post by guenter1910 on July 02, 2026, 08:52:08 AM »

I measured my way through the circuitry and discovered a broken link between C13 and R12. After fixing this everything seems to work fine. 

All the best
Guenter

3

First Aid / True Grit (Kit) not working

« Last post by guenter1910 on July 01, 2026, 05:23:50 PM »

Hi all,
I just finished the assembling of the true grit and unfortunately it is not working. The only thing that is working is the IN switch and the Blend Poti. All other switches and Potis have no function. I could measure the + and - 16 V on V+and V-. Also the tube is heating up.

Since I have not found any troubleshooting infos, I do hope to get support in the forum.

Any help is highly appreciated!!

Thank you in advance,
Guenter

4

SK49 Multi-patern Tube Microphone / Shockmount elastic

« Last post by Alex Harmer on June 30, 2026, 11:53:50 PM »

Hi JPK,

I noticed the elastic band in the shockmount has started to wear, after one of the mics received a small impact. The shockmount did its job, and the mic is not damaged!

However, I would like to know where to get a new elastic band. Are you able to show me where? Or can I buy one from you?

Thank you,
Alex from NZ

5

LA502T Tube Optical Compressor / LA502T REV1.4 modifications

« Last post by JPK on June 18, 2026, 06:53:57 PM »

D1, D2, D3, D4 diodes connections
These diodes add soft clipping, thus preventing abrupt clipping of the output stage.
The connections for these diodes are missing on the REV1.4 PCB. They can be restored by soldering short wires at the red line positions in the picture.

R16 replacement
It is recommended to replace the resistor R16 by a film capacitor of 100nF.
The leak current of C5 creates a voltage offset of about 20mV in the output stage when the gain pot is at 0. The cap eliminates it.

6

MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by JPK on June 07, 2026, 04:52:32 PM »

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MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« Last post by spurton@gmail.com on June 07, 2026, 01:18:00 AM »

Sorry yes R53. I replaced it and it works! I just recorded bass tracks through it and it sounded great. Thanks for the help. 

8

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« Last post by JPK on June 04, 2026, 05:30:55 PM »

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AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« Last post by terroirmusic on June 04, 2026, 04:36:02 PM »

It turns out I am, in fact, a dunce, and was misreading the value of C14 thinking it was correct. I got it and C5 mixed up. Swapped them and it is functioning correctly now.
Apologies for any hassle this may have caused, and thanks for your patience!

10

AB528 Microphone preamplifier / Re: AB528 build has an abnormally high noise floor

« Last post by JPK on June 04, 2026, 03:46:34 PM »

on the heatsink of Q5 (test point I) I get around -0.07V instead of -0.5V.
How much do you get on point F? and on the low side of R22?