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.

At 9:01 PM +0000 12/12/01, paulhaneberg wrote:
>
>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.

MOTM is quieter than any synth I have ever heard, and I got my first synth
in 1978.  I'm pleasantly surprised -- originally I was concerned about not
having an enclosed chassis.

>First you have two wires to ground on the power supply lines.

That lowers the ground impedance, which is a good thing.

>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.

I can't speak for Paul, but I'm sure he had patch cords in mind when he
designed the system :)

Btw, who did anyone win the LFO UI "contest" ??

It seems my most recent comments were misconstued as a complaint 
against Paul Schrieber and the design of the MOTM.  It was not 
intended as such.  I was merely pointing out that as in the case of 
the MOVs, theory is not always practice.  There are certain aspects 
of the MOTM design which I pointed out that do not necessarily 
follow theory but in practice work out very well.  Some of these 
including the dual ground wires are a trade off; potential ground 
loop vs. lower impedance.  
I have absolutely no complaint about the MOTM design at all, in fact 
it is superior by far to anything else I have encountered and I have 
owned probably 75 or more synths.
I'm just still looking for a definitive answer on the MOV question, 
if there is such a thing.
Paul Haneberg