Hello Florian

First of all thanks for taking time and answering me !

Today i did exactly what you wrote here. I took all the audio and electricity cables out .

My experience with modular system follows ;

Lets say;

-you have a module in case A
-you have same module also in case B
- And you have your outputs going to your mixing console from case C

When you connect the module in case A to case C , there is a hum .
When you connect same module but from case B to case C , there is no hum .

And sometimes if a module is making hum from Case A , when the time you connect another module from Case B somehow killing the hum coming from Case A .

Another example ;

lets say you have Cwejman MX4S mixer in Case A
And on Case C you have Cwejman AI

When you connect them each other , there is no hum , but when take something from Case B to MX4S where it is connected to case A , with this chain , output from Case C is also starting to make hum .

Seems like modules each other are able to kill the hum , but also modules each other are also creating the hum .

If Cwejman MX4S mixer is on high volume, but no signal inside , this is reducing the hum coming out from AI2 .
But when you start to volume down the channels of MX4S , hum is getting higher again .


As summary , hum is getting high and low also if you start to play the volumes of the devices .

Is it normal
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

As an example of grounding each other ;

Case A > Case B > Case C > Case D

After this point do i have to turn back from Case D to Case A too


Well, these are my experiments .

--- In Doepfer_a100@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
> Hi
>
> > I am having serious humming problem in my modular system .
>
>
> Did you monitor the Doepfer rig standalone (without any connection to
> the outside world but the powerconnectors - no MIDI!!!) and insert a
> headphone in a VCA out - it will be not extremely loud, but will be
> enough for checking. Is the hum also there without any connection to the
> outside
>
>
> If no: There is only one serious method for tracing a hum. Disconnect
> everything in your studio, and reconnect one cable after the other and
> check after each cable, whether the hum is added. And if i say
> "everything" I mean everything. All power cables, all audio, speaker,
> lan, midi, usb whatever cable. You start with no cable connected at all.
> Then you start from the beginning:
>
> Poweramp to poweroutlet and speakers to Amp -> switch on -> check
> Mixer to power and to Poweramp -> check -> switch Mixer on -> check
> Reverb to power -> check -> switch Reverb on -> check
> Efx-Send to reverb in -> check
> reverb left out to fx return left -> check
> reverb right out to fx return right -> check
> and so on...
>
> In my studio this took a whole day, but it was worth the effort.
>
>
> BTW: To my experience today to most likely source for humming are USB
> midi or audio interfaces which are supplied by USB instead of a separate
> own powersupply.
>
> Florian
>