[sdiy] Lies, damn lies, and ground references

[Dave Magnuson]

At 02:02 PM 4/2/03 -0800, Tim Ressel wrote:
>
>Hi all,
>
>Let this be a lesson to anyone who wants to build a
>system. My poor CVs have to go through some pretty
>rough neighborhoods. By the time the CV gets from my
>Midi-2-CV convertor to the VCOs, it looks like an
>episode from Cops. I am getting gate feedthrough,
>offsets, and RF noise. 
>
>Now I know this has been done successfully before, and
>without having to resort to fiber-optic patch cords.
>So I am going to have to tackle this thing
>systematically and see if I can vanquish some of these
>foes. This might call for Samurai Jack. Or at least
>some microbrews...
>
>--Tim

It's difficult to diagnose without knowing the particulars of the modular
but here's a few things I'd consider:

Are there any CV processing modules between the MIDI->CV and the VCOs?
These could be the culprit.

How does the CV output of the MIDI converter look with no load?  Try
loading the MIDI-CV with a dummy load (10K?) and see what happens to the
output.

Are all of your jacks connected together via a metal faceplate?  Perhaps
you're getting junk fed through the chassis?  

How does the CV look when only the MIDI-CV and VCOs are connected to the
powersupply?  Perhaps part of the problem is dirty power... try scoping the
V+ and V- rails with everything connceted.

Are you using bananas or shielded 1/8" or 1/4" cables?  If you're using
bananas, make some sheilded ones and see if the problem improves.  Make
sure the shield covers as much of the signal lead as possible, and solder a
ground wire and banana off of it.

Dave Magnuson

Resonant Frequency:
resfreq at hoohahrecords.com
http://www.hoohahrecords.com/resfreq/index.html
-------------- next part --------------

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.463 / Virus Database: 262 - Release Date: 3/17/03