Archive of the former Yahoo!Groups mailing list: MOTM

I Fully agree with the idea of star grounding, and the ferrite
beads, PCB ground plane etc. are also good for noise suppression.
However, these synths are loaded with potential ground loops. First
you have two wires to ground on the power supply lines. There
probably isn't a problem here as both are closely paralleled.
However, the modules are also grounded to each other via any and all
patch cord grounds and also very possibly through the screws and
rack rails, although the paint or powder coat may provide some
insulation. Ideally all patch cords should be grounded at one end
only.

Having said that, theory isn't the same as practice. In wiring my
studio I would only use patch cables with ground connected on only
one end as a second last resort. Often they make the situation
worse instead of better and often you are trading less hum for more
noise. The last resort is to use one of those horribly unsafe gray
AC ground adapters. This is not a smart idea, especially if you
have balanced line AC.

I still wonder about the MOVs though. I'm no expert on these
things. But aren't they variable resistors which have a high
resistance (impedance?) at low voltage levels but break down and
conduct at high voltages? If the breakdown point is current related
then I can see how several in parallel would require a higher
voltage before they conduct, but if the breakdown point is voltage
based, the number in parallel shouldn't matter. Also what is the
relation to the speed the surge travels down the wire to the time it
takes the MOV to breakdown? Unless the breakdown is virtually
instantaneous the surge is going to be traveling down the line to
some degree so it would make sense to have MOVs at more than one
location.