MOTM

There are two questions here.  One is whether analog and digital grounds 
can be connected together on a PC board connected to a MOTM-950.  The 
answer to that is, Yes, because the two are connected on the MOTM-950 
itself anyway.

It's a different question whether a module can propagate noise through 
the power supply connections into other modules.  I am sure that is 
possible.  If noise could get through simply due to the analog and 
digital grounds connected, then the MOTM-950 would be subject to this 
problem for *any* set of modules supplied by it.  Analog and digital 
grounds have to connect somewhere.  At one point is ideal.  The 950 
provides that point.

In the end whether you have a noise problem comes down to whether you 
*detect* a noise problem, i.e. you have audible noise or noise visible 
on a 'scope.  If you do, then it becomes a matter of tracing the source, 
and, if you suspect coupling through power supplies, it is a simple 
matter to disconnect the suspected modules to see if the noise goes 
away.  I haven't noticed noise from my Veeblefetzers (which have a bunch 
of LED's), but if I detected a noise problem, I would disconnect them to 
see if it fixed it.

I have my digital modules, including Veeblefetzers, the MOTM-650, CGS 
digital circuits, Blacet Miniwaves, etc., on separate power supplies 
from the VCO's, VCF's and VCA's in my synth.   Right now I have a 
MOTM-950 powering nothing but two Veeblefetzers, the MOTM-650, and two 
MOTM-800 envelope generators.  The other digital modules are on a MOTM-900.

-Richard Brewster
http://www.pugix.com

Mark wrote:
> On 10/26/06, Richard Brewster put forth:
>   
>> It depends on whether your circuit keeps analog and digital grounds
>> separate.  If it does, then there is no reason to connect these on the
>> board; they will be connected at the supply.  If the two grounds do
>> connect at the board, it is not cause for concern.  I am running a
>> couple of Veeblefetzer's off a MOTM-950, and the analog and digital
>> grounds do connect together on the board.  I asked Paul S. if this would
>> be a problem and he said no.
>>     
>
> I don't know what a Veeblefetzer does, or what sort of noise
> considerations there are in "Veeblefetzering".  However, if noise is
> a concern, as it would be in an audio or precision voltage module,
> then, imho, it is best to keep the digital and analog grounds
> separate.  If it were something like a logic module, then it wouldm't
> matter much.
>
>
>
>