91

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

« Last post by JPK on July 18, 2026, 05:01:47 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?

92

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by JPK on July 17, 2026, 09:12:26 AM »

OK, you may have an issue somewhere.
Please wait until I am back at work (end of July) so I can help you.

93

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

« Last post by noeqplease 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.

94

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by Slembones on July 16, 2026, 08:57:43 PM »

Found the measurements I made of a real 1073. Here’s the flat frequency response at a few different gains
flat to 50k Here’s the 1073 High shelf response 

95

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by Slembones on July 15, 2026, 10:18:42 PM »

This sweep has about 6dB boost and cut you can see the roll off. I also included a flat setting 

96

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by Slembones on July 15, 2026, 10:02:09 PM »

 the red Line is switched out and the blue Lin is switch in but with all bands "off"

97

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by Slembones on July 15, 2026, 09:41:51 PM »

the unit is beginning rolling off at 10K even with the band switches set to "off"

98

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by Slembones on July 15, 2026, 09:40:06 PM »

can I mod the unit to be flat to 50K and restore the shelf

99

EQ573 Equaliser / Re: EQ573-II ran in my lab

« Last post by JPK on July 15, 2026, 06:34:38 PM »

It is a shelf but it is followed by a high frequency attenuation after 20kHz caused by the compensation caps in the circuit.
Can you make another diagram with a +/-6dB correction?

100

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

« Last post by JPK on July 15, 2026, 06:26:40 PM »

Remove U1 and check again R5 right pin.
You can keep U1 removed until this is fixed.
Check the value of R5. It will be lower than 100k because of the other components around.
Checl the optocoupler is in the right direction.
Look for solder bridges or bad joints around R2, R3, R4 and the ratio switch.