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LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: August 20, 2026, 06:30:57 AM »

UPDATE:

I spent some time away from testing this compressor. Glad I did.
I saw some new test equipment, so I ordered a few new items to replace my aging oscillator and old as hell multimeter.

So, in the end it turns out that it was my test equipment that was not happy with this compressor.

Today I tested the LA 502 compressor I thought was bad, and it wasn't. At all.

Lesson: Always test your testing equipment, and always test your wires, leads, alligator clips, etc.

Thank you for your help and patience. Time to order a few mic preamps now

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LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: July 18, 2026, 06:12:16 PM »

All seems to be good when U1 is removed.
So the issue must be around U1.
Check the value and solder joints of R6, R7, P1, C5.
Check with another OPA2134.

You said the device is not working, but you did not specify what the symptoms are?

Hi JPK,

Will do these tests as soon as I am able to. 
First I'll turn it on with the current op amp, and write down all the symptoms for you, then go on to the tests, including using a different OPA2134.
Thanks.

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LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: July 17, 2026, 05:11:44 AM »

Thanks JPK,
So, reporting on your suggestions:

1. Removed U1.
2. R5 value is 17.3 kOhms
3. Optocoupler in correct orientation, checked against the other compressors which work, and on the board itself.
4. Renewed all solder joints for R2, R3 and R4, and scrubbed to remove any possible solder bridges, none seen under magnifying glass.
5. Checked VAC of R5 right side pin, reports 0.514 VAC, better than the previous value of 0.025 VAC.
Additionally I re checked TP1 for VDC and now it reported 7.8 mV DC.

Thanks.

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LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: July 14, 2026, 07:09:10 AM »

pic of the OPA2134 tests...

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LA502 Optical Compressor / Re: 502 Compressor not working - test results.

« on: July 14, 2026, 04:41:11 AM »

Just tested all 6 OPA 2134 ICs, all passed the test, both amps on each IC.

Will continue testing...

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LA502 Optical Compressor / 502 Compressor not working - test results.

« on: July 13, 2026, 04:16:31 AM »

Hi,

So one of my 4 LA 502 compressors did not work when first turned on. today I tested all the items on your handy troubleshooting list.

1. Checked for bad / cold solder joints, did not find any visible ones. Tested some different places on the circuit, and was able to get readings everywhere pretty much.
All ICs, transistors, and capacitors are in their correct orientations. No leads are near the chassis plate at all.

2. Checked DC voltages: + voltage is 16.14VDC, - voltage is -16.60 VDC. On TP1 I do get 1.105 VDC with the circuit bypassed, 1.04 VDC with the circuit engaged. So, there is some issue.

3. Applied a 1 VAC 1kHz signal to the input to follow it: Black probe on 0 V point.
R2 right leg reported 0.69 VAC
R 5 Right leg reported 0.025VAC with circuit in bypass, 0 VAC when engaged. REV 1.4
TP1 Reported 0 VAC, and no change when turning the GAIN knob.

So, something is definitely up. Please let me know what else I should test and how, so I can pinpoint the issue.

Thanks!!!

PS the other 3 compressors work beautifully.

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

« on: July 12, 2026, 04:11:53 AM »

Thanks!

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

« on: July 05, 2026, 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!