Hello,

you did not truely answer the central question:

does the hum exist, if you do not connect the Doepfersystem to any
mixer, but use a VCA-out or A138-Mixerout with an headphone

If yes: the fault is in the Doepfer system.

If no: the fault is in the groundwiring of your power connections.


Florian

timbre1096 schrieb:

> Is it normal

no

> In this case , grounding 4 Doepfer cases are sense
> If yes , what is the proper method to do it I have exactly the same yellow green grounding cable . What i tried was , connecting grounding points of the 2 racks together .
> But is that enough

The Doepfer system needs no additional ground, but it definitely
requires that all connected devices (A100 racks, external mixer,
poweramp, effects) share one common power ground. The power connector of
all A-100 racks MUST be three prong connectors and the multi power
socket bar must use all three lines.

Florian