Re: [AH] Doepfer Opinions (PSU CROSSTALK)

From Plan B (Peter Grenader)
Sent Fri, Feb 8th 2008, 15:11

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On Feb 8, 2008, at 4:52 AM, Florian Anwander wrote:

>> my main concern with Doepfer is quality, are there any issues with  
>> crosstalk
>> or quality of rails n PSU?
>> i remember reading somehjting about it, but have none personal  
>> experience.,,

> No. There is no "crosstalk",

Um...with all respect, there most certainly is an issue with  
crosstalk with current Eurorack power busses. The ground connections  
on the bussboards are daisychained, which results in an open path for  
noise created by one module to be  transmitted down the line.  As a  
result, VCOs and some filters placed in the same rack (powered by the  
same PSU) as LFOs, EGs, and modules which use PICs or Microp's and  
others which are notorious noise makers will cause the zero  
transitions of these listed modules to be heard at the outputs audio  
modules which share the same power.  So by noise I don't mean white  
noise, but I so mean clicks, hums and audible LFO oscillations in the  
signal path. This effect can be lessened by connecting the power to  
any audio modules in shared racks as close to the main power inputs  
as possible.  This works in some instances.

There should have had separate ground traces running from each of the  
connectors on the bussboard directly to it's power input terminals  
which lead to the PSU.

There is a fix however if you've using racks in duplicates of two  
(meaning an even number of rack cases), but it'll cost you two more  
bussboards per pair:

If you purchase an extra bussboard per rack, mount a second into each  
of the cases, then make separate cables coming from the two PSUs (one  
in one rack, one in the other) and interconnect them so that one PSU  
in one rack powers one bussboard in each of the two cases, and the  
PSU in the second case powers the others bussboard in each of the  
cases, then you've created separate power systems for audio modules  
and control modules.

- P

Peter Grenader
p: 888 791-0010