Hi Scott

> I’m still interested in knowing what the original cause of the hum is (and a solution) if anyone knows.

Hum can be a very complex topic. To know the cause one would have to
know all your equipment and all the cabling. That is not doable via the net.

25 years ago I did a lot of installations and the reconfigurations of
professional recording studios. To find the cause for a hum, we usally
unplugged everything(!) and then reconnected one cable by one, testing
after each new cable. We used a scope for the monitoring (sometimes also
a battery driven speaker for listening) and started always with the
device which seemed to have introduced the hum.

Typically people have a low level basic hum, which they ignored for
years, and then they add a device which makes this (former) low level
hum very appearent. So assumingly the Doepfer rack is not the cause, but
it is the piece which "puts the finger" on the weak spot.


In modern computerized studios there is one device which quite often is
the cause for hum: the monitor of the computer. But this is only a blind
guess. But it is often helpful to remove all connections to/from the
computer (USB, Firewire, analog out from the headphoneout of the
laptop...) from the interface and the analog audiogear.

Florian