Moog Music Forum

Hey guys,
my DFAM VCA Out ist dead, no sound, nothing. All other works, also the single VCO outs.
Any idea?

Thanks....

The block schematic diagram of the documentation implies an analog technology behind. If that's true you will find an OTA like the LM13700 serving as VCA. Check the input and output of that OTA with a scope to see any signals reach and pass the VCA. If the output is dead, just replace the OTA.

Hi
I've run into an issue with my Dfam, making random click noise , I think related to the VCA (decay?), it always seems to happen when it reset to the first step.

Any idea?

Thanks

A silent VCA out doesn't necessarily mean the VCA is dead. If the VCO mixer or the VCF or the VCA EG are dead, you would still get nothing at the VCA out. A few easy things to try:

Plug in into a mixer or amp and turn the gain up until you can hear the background hiss of the DFAM.
If you turn the volume, does the hiss level vary - if so the is before the output stage.
Do the filter controls alter the hiss in any way? If they do, the fault is before the filter.
If you stick a CV into VCA CV input, does it vary the noise? That would suggest the EG isn't working.

Hope that helps narrow it down a bit...

Steve

SPR wrote: Sun Sep 07, 2025 11:16 am A silent VCA out doesn't necessarily mean the VCA is dead.
...

Yes, so at the end you must do a kind of back tracing. Start at the VCA and "follow the rabbit" backwards to the saw core or whatever the first sound source is.