Power supply musings

[harry bissell]

Whoh! Heavy topic...

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.

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

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

macdonald at evenfall.com wrote:

> I have some basic questions about bipolar power supplies.  Most designs
> seem to use a center tapped transformer with the center tap acting as
> ground (the mains ground wire is connected to the center tap I believe)
> and the other two outputs going off to the rest of the supply
> circuitry.   To me this means your supply ground is then a "real"
> ground, compatible with your other, similarly grounded, equipment.
>
> Then there are other designs which don't use a center tapped
> transformer, one output acts as ground and the other output seems to
> feed both the plus and minus conditioning circuitry of the supply.  I
> have not seen one of these with a mains ground wire connected in to the
> circuit.  What is the reason for this?  Wouldn't the "virtual" ground
> created have the potential to cause ground loop problems when the
> circuit was connected to other equipment?
>
> The latter design does seem attractive because you could use a simple AC
> output wall wart (cheap, easy to find) to drop the voltage to a safer
> level before it even enters the enclosure.  But without a mains ground
> connection it seems the potential for grounding problems is increased?
>
> Thanks,
>
> Chris MacDonald