Hi



1. No the rails are not connected to ground. This is the way Doepfer built the box and I was not advised to change it.

1b. I do not know if the power supplies are connected to ground. They are covered metal boxes. I would have to rip them open to find out. There are ground wires in the power cables so I assume they are, however, my tech is telling me this is caused by a badly designed power supply so I can’t be sure. For info, I first bought a pre-assembled Doepfer Basis System 2 and then added 2 additional LC9 cases later.



2. All power in the room comes from a reasonably good quality UPS that outputs a pure sine wave. There are over 20 synthesizers, a rack of effects and other synths, plus guitar pedals, other gear, 2 Genelec monitors, and a computer with 2 monitors, all powered from that one source. And as I said, there is no hum in the room except when I connect one of the Doepfer LC9 cases. When I patch something from a second LC9 the hum gets twice as loud.



3. I suspect the power supplies will have to be modded to fix this so for now I have just purchased an Ebtech Hum Eliminator. I will put the audio output through this box for now and see if it removes most of the hum until I can find a more permanent solution. I have decided to do a little rearranging of modules since I had the main case apart anyway so I will report back in a couple of hours on how this works.



I’d still like to hear any other technical information or ideas that might help understand what is causing this, though!



Thanks

Scott





From: Doepfer_a100@yahoogroups.com [mailto: Doepfer_a100@yahoogroups.com ]
Sent: Sunday, June 12, 2016 11:15 AM
To: Doepfer_a100@yahoogroups.com
Subject: Re: 1 Re: Loud ground loop hum





Hello

1.) are the power supplies and the rack rails connected to ground
2.) is your studios power distribution wired as star system It must be
based on a single wall outlet socket and then a central power "multiple"
(I don't know the right english word for that, sorry). Or you must be
very sure, that all wall outlet sockets are based on the same electric wire.

Florian

Am 12.06.2016 um 14:22 schrieb 'Scott Rogers' scott@...
[Doepfer_a100]:

> HI
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> Thanks but that’s a very dangerous idea and not really a solution. There has to be some explanation of what’s going on and a much better, permanent solution.
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> Scott
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> From: Doepfer_a100@yahoogroups.com [mailto: Doepfer_a100@yahoogroups.com ]
> Sent: Sunday, June 12, 2016 8:00 AM
> To: Doepfer_a100@yahoogroups.com
> Subject: 1 Re: Loud ground loop hum
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> Hello Scott,
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> Try to disconnect the Doepfer mains from earth.
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> Jacco Ville
> The Netherlands
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> Posted by: "Scott Rogers" < scott@... >
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> Yahoo Groups Links
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