[sdiy] More ground questions

Dave Magnuson resfreq at hoohahrecords.com
Thu Aug 1 19:02:14 CEST 2002

At 09:23 AM 8/1/02 -0700, Scott Stites wrote:

>Also, I have a book called "Build a Better Synthesizer"
>by Thomas Henry in which he recommends that shielded
>cable be used for module-front panel interconnection
>and that only one end of the shield be grounded at the
>module itself.  I’m wondering, is this standard
>practice in the Synth DIY world?

Hey Scott,

I think the use of shielded cable is a good idea... although I don't
usually put it everywhere.

An example:  For LFO or EG outputs I don't usually use shielded cables...
But: Audio inputs/outputs, gain controls, or anything with audio on it gets
shielded.  It would be ideal if you used shielded cable everywhere (keeping
noise from radiating OUT of CV wires), but I find it expensive and harder
to work with.

Originally, I didn't shield anything, and usually there wasn't a problem.
On a few modules (especially ones w/ makeup gain) I got a little noise from
adjacent CV wires... so I reinstalled sheilded cable after-the-fact.  Now I
tend to build stuff with shielded wire on audio paths.  I also tie the
shield only at the PCB end.  If I need a ground on the panel control, I run
a seperate wire, rather than using the shields.  

Also, you'll find that on some PCB kits (Paia, EFM, etc) it will be
difficult to tie the sheild to ground... there may not be a ground near the
connection point.  This gets akward to deal with, and a little messy too... 

Most of my noise problems were when modifying a pair of SH-101's.  There
wasn't enough room in the case to get the knobs very close the the circuit
board... so there are a few 12" or 16" wires in there that were picking up
LFO/clock noise.  Replacing them with shielded wire really cleaned it up

Dave Magnuson

PS... I definitely recommend the seperated dirty/signal ground.  I use the
.156" Molex connectors ala Blacet, Synthesis Technology, etc.  They use a 4
conductor cable, making this pretty easy to implement on your home-brew
modules while still following one of the popular standards.  If possible
tie the two grounds togther only at the power supply.  You could do it at
the distribution board, but I prefer to do it right at the power supply.  

Resonant Frequency:
resfreq at hoohahrecords.com

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