chassis grounding

Tom May ftom at
Sat Aug 10 01:43:30 CEST 1996

Gene Stopp writes:

>Within a self-contained system such as a synthesizer I always just 
>ground everything together - the circuit board ground, the panel, the 
>jacks, the box, and the third prong of the AC power cord. Works fine 
>for me so far. I think that you only run into ground loop problems 
>when interconnecting machines together whose AC power comes from 
>different and/or distant outlets.

I had ground loop problems on a tube amplifier that had effects loop
jacks grounded to the steel chassis.  I got a lot of hum reduction by
replacing them with nylon-bushing jacks and grounding them at the
power supply.  On the other hand, Mackie highly touts their metal
jacks screwed directly to the steel chassis.

>You can lift the synthesizer housing from the third prong if you want 
>to avoid potential ground loop problems. What I would do in that case 
>is make sure that the power supply ground terminal (usually the center 
>tap of the bipolar supply transformer winding) is connected to the 
>box, jacks, and circuit board ground.

That's just like using a three-to-two prong (ground lift) adapter,
which is a reasonable fix for something you didn't build yourself,
although you lose the safety advantage of having the chassis directly
grounded.  For DIY, I have thought the better solution is to use the
chassis as a shield and a safety by connecting it to the middle prong,
then ground all the signal stuff (power supply, jacks, circuit board)
together and call it a signal ground, then ground the signal ground to
the chassis ground through a ground lift switch.  That way the chassis
always has a beefy ground connection, but ground loops can be
minimized by opening the ground lift switch if necessary.

There are a couple books I'm planning to look at some day that should
be more authoritative: "Grounding and Shielding Techniques in
Instrumentation" by Ralph Morrison, published by Wiley, and "Noise
Reduction Techniques in Electronic Systems" by Henry Ott, also
published by Wiley.


More information about the Synth-diy mailing list