VCA bleed thru

[Rarecomponentadsr]

Not quite MiniMoog but nearly.

It’s about a MIDI DAC VCA module based faithfully on the Minimoog circuits.
This is a module by AJH synths and I have two however one has started to leak an audio signal even with all controls set to off.

AJH told me it’s probably one of the Trim pots breaking down . There are two 100ohm ones as per the Mini vca circuit., however I’ve adjusted both these and it’s making no difference to the leaking audio.

I wonder if anyone has any info regarding this issue ?

[analogmonster]

Assuming you refer to the discrete VCA of the original Minimoog schematics:

The VCA is opened and closed by the current sink Q18 (Minimoog service manual). If there is an audio leakage in your device I would check the base voltage of the equivalent of that transistor in your device first (contour input). If it is not zero, the contour control (envelope?) does not go to zero and therefore does not close the VCA totally and the audio material is not attenuated correspondingly.