Power supply musings

[Martin Czech]

> IMHO  (not too "H" I might add) the DC power supply ground should not be
> grounded. I open my equipment and remove such grounds from the audio path,
> though I would leave the metal chassis connected if ALL in/outs were
> isolated.
> 
> There are often 3 grounds in an audio chain... One is the audio shields...
> One is the mains ground... and one is the sneaky path from chassis to
> chassis.
> 
> If you break the audio shields, you are asking for noise problems...so I
> break the mains ground... and isolate the chassis from each other (humfrees
> are a commercial variety of the technique I use, nylon shoulder washers)
> 
> Noise is gone. Some say that I am at risk this way (safety)... I think the
> audio cables are more than adequate to handle the fault currents long enough
> for the breaker to trip. Most Audio gear can have the "3rd pin ground"
> safely plugged into one central common point. I pulg into the wall at
> exactly one point, and run a dozen outlets right from that point.

If it is ensured that your transformer has certain isolation properties
and your internal wiring IS safe, you don't need to have mains ground
connections at all.  Most music instruments are that way, they have only
two pin connectors, even if they are 19" metal "bricks".

Modern fault current detectors will sense any differential current
in the two mains lines, so in case of problems they will switch off.
Older models just sensed to return current in the mains ground , this
will of course not work if the faulty aparatus has no such ground.

I think such an interrupter is a very good investment, at least for your
workbench if not for the whole house. 

The bad thing is that you can't kill your wife by throwing the hairdryer
or shaver into the bath tub any more. (THIS IS JUST A JOKE. DON'T TRY THIS
AT HOME).

OTOH, in case of secondary high voltage like in tube amps a mains ground
connection to signal ground is a MUST.

> 
> The ground of the non-center tapped transformer can't be mains grounded if
> it uses a full-wave bridge rectifier... half-wave can be. It is really hard
> to generalize like this because all designs are different. In my 360sysems
> Midi Bass (rack) ther was a 5V regulator whose tab (ground) touched the
> chassis. This was audio suicide. When isolated (mica washer) all problems
> were gone

Yes, half wave. This is the big disadvantage of this simple transformer circuit.
Not recommended for severall amperes, but good enough for a stomp box.
 

> Watch out for MIDI cable grounds, they should have the shield grounded ONLY
> at the transmitting end of the cable, Never at the receiver. This can be a
> fourth ground problem.   Flames welcomed !!!! :^) Harry Bissell

It can be, but I think only with a faulty internal grounding circuit.

m.c.