OK, I'll offer up an opinion and disclaimer.
I did not exactly follow John's recommendations. But, I did use up all the
ground pads available on the PCB. You will notice I combined some grounds
and not others. I did not mix CVs and audio or anything else that logically
made sense to me might interfere with one another (which seemed to be John's
basic approach too from my casual observation).
Here was my small brain's thought process. In an unbalanced scheme, there is
as much signal current in the shield as the signal conductor. So, if you
have only one wire from jacks to PCB, then all these currents mix on the way
to the PCB. And, no matter how hard you try to keep them separate, you
cannot completely because they jacks are all quite well bonded at the panel.
So, some interaction between CVs and audio caused by the voltage drop in the
ground connection will occur. Ideally, there would be no common path
(isolated grounds, isolated path on the PCB). But, that of course is not
the case.
My thought was that I wanted as little interaction between I/Os as possible.
So, that meant to keep the R of the ground connection from jacks to the PCB
very low. Therefore, I went with the multiple wire method. I assume the
single wire method might work just as well, provided the wire was not
significantly undersized. Since there is a limit to the wire size that can
connect to the TM PCB, the multiple wire path made sense to me.
Disclaimer: I don't posses the educational accreditation to support my
theory. This is not meant to be an instruction on how it should be done,
but rather an insight on what I was thinking when I largely just followed
the designer's recommendation and made my own decisions. I have never built
any of my modules with the "strap 'em all together, one ground wire" method.
In fact looking at my Multimix, I see I used shielded I/0 and used heat
shrink near the PCB where I tapped the PCB end of the shield to run a ground
wire over to the SCRN connection (unless using the adjacent ground
connection). I am also not offering any criticism to the other methods.
Larry (now you know how my crazy brain works somewhat) Hendry
P.S. Since the TM is basically a "lo-fi" device AND according to our quiet
list friend Harry B, "BDDs suck" does it really matter?
----- Original Message -----
From: thomas white <djthomaswhite@...>
To: <motm@yahoogroups.com>
Sent: Tuesday, February 26, 2002 8:33 AM
Subject: [motm] Conversions Question
I am in the process of converting my Blacet Time Machine to MOTM format and
pose this question. Since all of the grounds on the Blacet schematic
individually "star" back to one point on the pcb, can't I simply connect all
the jacks with unshielded wire in a star type web and run one connection off
this web to the pcb ground for the same overall effect? I used the
unshielded wire method and it appears to work fine. Although in looking on
Larry Hendry's page I noticed that his model uses Blacets wiring scheme
while Dave Hylander uses the "Oakley Type" unshielded wire approach as I
did. Comments?
Thomas White
PS. Nice to not have to fiddle with 1/8 cables anymore :)
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