Losing my mind: Erica Synths VCA v3

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the_laconic
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Losing my mind: Erica Synths VCA v3

Post by the_laconic » Mon Feb 15, 2021 12:27 pm

I am at my wits' end with this one.

The second VCA doesn't work in dual mode. I have traced the audio signal forward and backward using the schematic. Audio comes in fine, signal materlalizes at the output of the op amp at DA1, but just disappears when it hits the single/dual switch after that. So there is no input to the AS3360 at pin 9. The control signal seems OK, it's just that there's nothing to control by the time it hits the IC.

The switch itself seems to work when i flip it either way and test for continuity where it's supposed to be. When I flip it "off" (down), which is supposed to be dual mode, I would expect from the schematic that it would connect pins 2 and 4 on the top left header, but it doesn't seem to -- no signal ever appears on pin 4.

Is the header damaged? The switch? I would have guessed the AS3360, but I'm pretty sure that works fine for the first VCA, and in single mode.

I really tried to troubleshoot this sucker myself, but now I throw myself at the mercy of the muffwigglers.

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EATyourGUITAR
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Re: Losing my mind: Erica Synths VCA v3

Post by EATyourGUITAR » Mon Feb 15, 2021 12:31 pm

did you check the control inputs with an oscilloscope? 0 to +2v linear control voltage. if you have CV but no audio passes then you have a bad AS3360. you must do this test to determine if the AS3360 is bad. there is no other way.

http://www.alfarzpp.lv/eng/sc/AS3360.pdf
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the_laconic
Learning to Wiggle
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Re: Losing my mind: Erica Synths VCA v3

Post by the_laconic » Mon Feb 15, 2021 12:54 pm

I checked with an oscilloscope that there is a CV running between 0 and +2v at pin 10, yes.

Hmm. When I flip it to Single, I get audio coming in on pin 9, but no output either. I guess I should bite the bullet and try replacing the AS3360.

Thanks. I'll report back once I get the chip.

the_laconic
Learning to Wiggle
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Re: Losing my mind: Erica Synths VCA v3

Post by the_laconic » Mon Feb 22, 2021 4:35 pm

I popped in a fresh 3360, and... that's not the problem. I wonder if it's the switch...

the_laconic
Learning to Wiggle
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Re: Losing my mind: Erica Synths VCA v3

Post by the_laconic » Mon Feb 22, 2021 6:13 pm

Gah, I've been counting the pins wrong on the 3360. (Why do we have dots AND notches...?)

the_laconic
Learning to Wiggle
Posts: 17
Joined: Tue Feb 02, 2021 12:50 pm

Re: Losing my mind: Erica Synths VCA v3

Post by the_laconic » Mon Feb 22, 2021 7:35 pm

I'm not sure there's even a problem here, except for one or more of the following:
1. The calibration instructions refer to v2.1, and something changed in v3 so that they no longer apply as written.
2. The single and dual modes are switched.
3. Single and dual mean the opposite of what you expect.

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