Duck no audio pass through
hey there, I`ve built a Duck, checked for cold joints, right orientated components and so on. But no matter what I try I cannot get audio out of this module.. the yellow led is constently on. red led works with gates and settings.
Any idea, what do to check first?
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Hey Nys, I would start with the VCA/main board:
Reflow suspicious solder joints, start with the ICs.
Check the board connections with the headers
Check the supply rails: +12 V / -12 V at TL074 and LM13700 (U2), and the +10 V reference around LM4040 (IC6) and U1 (Pin 1).
With no audio connected, measure VCA_OUT DC (lower pad of R31) voltage. It should be close to 0 V. If it is strongly positive, negative or near a rail, check U1B, R31, R32 and LM13700 (U2), especialy for solder bridges or bad joints.
Apply a gate and measure CV_TO_VCA (left pad of R15). The voltage should clearly change with the envelope. If it does, continue through U1C → Q2 → LM13700 pin 1. This is the VCA control-current path.
The constant yellow LED is especially interesting because its driver monitors VCA_OUT. So I would measure the DC voltage at VCA_OUT first. If you send me that voltage plus the voltage at CV_TO_VCA with and without a gate, we can narrow it down quickly. Thanks,
Stefan