Tube power supplies & grounding

[Harry Bissell]

The common practice in most Guitar Amplifier circuits (USA) is to use the
Chassis as Audio Ground, and then reference that ground to "neutral" via a
.05uF/600V capacitor.
Problem is you don't know which side of the line is "neutral" in all cases
(bad premesis wiring etc...) So they use a three position switch and allow the
cap to be connected to either side of the line... or floating.

It is my experience that the "floating" position often gives the lowest hum /
noise. And tying the chassis to one side of the line can give some funny
little "pokes" here and there if
you run into another chassis capacitivly coupled to the "other neutral"
line...

I'd try it out and see what you like. IMHO I'd use a switch that allows you to
select how the grounding is accomplished.

P.S. Note I have not mentioned "earth ground". It should be at neutral
potential in the USA. If you ground to this... be sure it is really earth...
(read connected to anything... connected to the RIGHT thing etc...) The
Hardware store sells little testers that have three
neon lights... get one and use it. Cheap insurence policy. Take it on the road
too...

I WOULD NEVER tie the chassis direct without the cap !!! I like my life too
much. I made other band members DISPOSE of their equipment that had
potentially hot chassis
(an old Traynor for instance) after these amps ganged up and tried to kill me
!!!
:^) Harry

Doug Tymofichuk wrote:

> Happy New Year, everyone!
>
> I have completed building a power supply for my tube synth
> (see attached gif). When I built the dual VCO module, I
> built separate high voltage and filament supplies just for
> it on the VCO chassis. So this power supply just supplies
> 120 VAC to the VCO and then all the other appropriate
> voltages for the rest of the synthesizer.
>
> There is a time delay relay that keeps the high voltage off
> (standby) for 30 seconds to allow the filaments to heat up
> first.
>
> All filament power supplies are completely isolated from
> the rest of the circuitry.
>
> The DC common/signal grounding system is set up as a "star"
> ground, and is not connected to the chassis earth at any
> point. My question is this: should the chassis/AC earth
> ground be connected to the DC common/signal ground
> directly, through a small capacitor, or not at all? (See
> dotted symbols in centre of diagram.)
>
> Any other comments/suggestions/flames?
>
> Thanks in advance!
> ----------------------
> Doug Tymofichuk
> dougt at cancerboard.ab.ca
>
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>  [Image]