240volts and ground hum problems.

[Martin Czech]

> Dear Larry,
> and synth diy list 
> in Europe the power is different,
> 240 volts 50 Hz .Most domestic buildings don't have 3 phase supplies, 
> so you have Live neutral and Earth connections.

? 

I think every electric kitchen oven has 3 phase supplies,
and how would you connect your circular saw?  I think every house
has a 3 phase mains connection in the cellar...

I wouldn't say that 120V is less dangerous then 240V, it depends on the
situation.

For small signals balanced audio is the only way that allways works.
Shield connected to both ends to grounded chassis and twisted pair cable
(some cables are not twisted, even microphonme cables are sold this
way!! ). Even today some machines are wired inside such that signal
ground and chassis ground connect.  That is very "clever", because now
the expense for balanced audio pays in a super hum unless one side is
ground lifted.  But ground lifting will effect the hf shielding in a
negative way.

Pro equipment is allways balanced, even with severall volts signal amplitude.
It is ridicolous to have unbalanced connections an one hand and 20 bit ADC
or more at the other. My home studio is quite silent, no large industrial
power consumption etc. But with unbalanced cables I won't get the hum and dirt
much more below then -86 dB or so (FFT in cool edit of Soundscape input, mixing
desk fader down).

For live playing and outdoor playing there is only one method: transformer
coupled balanced audio. Inside your 19" rack you should have no more
problems then at home, but the fun starts if cables are running a couple
of meters across the stage and elsewhere. There is stage light (dimmed,
hf dirt). If you know nothing  about your ground potentials at different
places on stage or back stage or far away from stage at the mixing desk,
this is the only possible way. Electronic balancing isn't made for large
common mode voltages.