MOTM

Ideally, you would like to see each signal to a panel jack have a ground 
point on the board, which connects straight out to the jack ground.  
Most (if not all) MOTM modules are wired like this.  However, there is 
an advantage in twisting a grounded wire with signal wire, even if it's 
grounded at one end only.  You will get some shielding effect.  (If 
grounding to a panel jack, make sure that some other wire returns the 
jack ground to the board.  You might buss all the jack grounds together 
and run one ground wire from near the power connector on the board.)   I 
try to find a ground point on the board for each signal wire, even if 
it's not right next to the signal connection.  Multiple ground wires can 
share a single ground point with a little creative wiring, too.  Loop 
one around the other and solder, leaving a single wire to insert into 
the ground hole.

Someone may comment on ground loops, which can cause unwanted 
oscillations.  A ground loop is formed when there are multiple ground 
paths for a signal to follow.  I have never encountered a problem that 
turned out to be caused by a ground loop, that I know of.

As to using the normal lug to ground inputs, it depends on the circuit.  
Any input that terminates at an op amp summing node can be grounded.  
But if going into a comparator (like the MOTM-120 inputs) or to a 
passive mixer network (MOTM-490 inputs), then you do not want to ground 
the input when it is unused.

Richard Brewster
http://www.pugix.com

Mark wrote:
> Does anyone have any thoughts on using twisted pair cable when there
> is no adjacent ground connection on the PCB??  For example, most
> third-party PCB's do not have ground connections near the jumper
> connections for CV inputs and outputs.  However, they usually have a
> method of connecting the shields of all the jacks to ground.  So if
> the panel end is tied to ground, is there an advantage in using
> twisted pair cable when connecting a CV's to the PCB even when the
> ground wire is not connected at the PCB??
>
> Also, as a general rule, should unused high-impedance inputs be
> connected to ground using switched jacks??  Some of the MOTM
> instructions say to do this, while others don't.
>
>