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

« Last post by Slembones on July 20, 2026, 07:48:39 PM »

I have traced it to the discrete amps circuit with a scope. my component installation is correct. I think the feed back circuit at the end of the descrete op amp is rolling off the highs too soon? (guess). it is happening in both amps the same. the feedback (470pf on A and 150pf on B) cap on the outside of the circuit has little to no effect.  could I have a bad component? 

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True-Grit Tube saturator / Re: TRUE GRIT Problème

« Last post by JPK on July 20, 2026, 08:34:54 AM »

Vérifiez le potentiomètre P1 : 20k entre les pins extrêmes, 0 à 20k entre la pin centrale et les pins extrêmes, en fonction de la rotation.
Vérifiez les soudures de P1, R5, R7, C9.

Vérifiez les connexion entre le switch SW2 et le connecteur J1 :
- pins 1-2 (à l'avant du switch) vers J1-pin2
- pins 3-4 (au milieu) vers J1-pin1 (pastille carrée).
Si une connection est coupée, il faut la réparer avec un petit fil.

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True-Grit Tube saturator / TRUE GRIT Problème

« Last post by Loudwig51 on July 19, 2026, 09:49:37 AM »

Bonjour 
J’ai un problème avec mon TRUE GRIT. Le son passe mais le potard de drive et le boost ne fonctionne pas, tout le reste fonctionne.
Le son sort comme si le drive était à fond et le boost enclanché.
Au montage, j’avais soudé les 4 boutons à l’envers sur le petit PCB, entre temps en tentant de dessouder j’en ai cassé un, un ami m’a prêté un pistolet à dessouder et j’ai pu récupérer les 3 en bon état et j’ai commander un quatrième.
Il s’avère que le bouton commandé est soudé sur le boost actuellement.
C’est peut être cela le problème, ou en utilisant le « dessoudeur » j’ai abîmé le petit PCB.
Seriez vous m’aider
Merci d’avance

Ludo

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

« Last post by noeqplease 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.

« 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?

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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.

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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.

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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 

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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 

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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"