DVCA build problemos?

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breadman
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DVCA build problemos?

Post by breadman » Wed Jan 23, 2019 6:24 pm

Hey all, unfortunately I've spent the better part of a day troubleshooting a DVCA to no avail. Channel 1 works fine, but Channel 2 does not pass any input or respond to knob-turning. The normalization of Channel 1 to Channel 2 is okay and the bicolor LEDs respond when Channel 1 is normalized so the problem is definitely happening pre-U4. I'm pretty sure I've reflowed the whole board at this point and checked continuity on everything against the schematic.

One issue I noticed is that Pin 11, the VC input for the working side, typically reads at about 0.3V at maximum pot setting while Pin 6 is at +10.3V or so, though I can't detect any short between that pin and positive power or 10V reference. Likewise, C3 has very little voltage across it and C4 has 10V or so.

Anyone have any helpful hints where I might look next?
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merlin
Learning to Wiggle
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Post by merlin » Wed Jan 30, 2019 11:33 am

breadman wrote: One issue I noticed is that Pin 11, the VC input for the working side, typically reads at about 0.3V at maximum pot setting while Pin 6 is at +10.3V or so, though I can't detect any short between that pin and positive power or 10V reference. Likewise, C3 has very little voltage across it and C4 has 10V or so.

Anyone have any helpful hints where I might look next?
You will not get anything through the VCA with 10 Volts on the control i/p, pin 6 (+3.3 Volts give -100dB attenuation which is the maximum), hence the reason why there is no signal at CH2 out. I would check the – supply on the amp with C4 across it and that C4 is soldered correctly, if not, or it's open circuit, the amp will have a very high gain. The C4 op-amp may also be faulty.

Just some thoughts on your issue, hope it’s of help.

Karl

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