ADSR/VCA problem(Solved)

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Sparrows78
Learning to Wiggle
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ADSR/VCA problem(Solved)

Post by Sparrows78 » Fri Mar 16, 2018 10:26 pm

I just finished building the ADSR/VCA and having problem with the VCA. The output just gives a steady voltage, it doesn't get affected by triggers or the adsr. If I send audio to the VCA input, the VCA output sends the same signal out unaffected.

The ADSR out seems to work the way it should, controlling filters etc. in all three modes, both looping and with gates. The led works as it should.

I have checked all connections, reseated all ICs, replaced u5, u6, u7.

I have tried to follow the schematic as far as I can but starting to run out of ideas - I would appreciate any help I can get :)
Last edited by Sparrows78 on Mon Apr 09, 2018 5:18 pm, edited 2 times in total.

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Synthbuilder
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Post by Synthbuilder » Sat Mar 17, 2018 4:00 am

Does the 'GAIN' trimmer change the level of the signal at the output of the VCA? If so, the VCA itself may be working fine but the VCA control signal may be at fault. This may indicate a problem with the circuitry around the right hand side of U5 - perhaps even Q5. Check Q5 is a BC560.

Tony

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Sparrows78
Learning to Wiggle
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Joined: Sat Feb 03, 2018 5:37 pm
Location: Sweden

Post by Sparrows78 » Sat Mar 17, 2018 8:34 am

Following your advice I manage to find out that Q5 was not working as it should. I replaced it temporary with a 2N3906(reversing the pins) and the module is working like a charm!

Thank you for your help! :)

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