I have been reading various posts on various Fora about:
* use of 2- or 3-cord mains cables,
* relation of signal ground to mains earth,
* unbalanced IC construction,
* signal ground connection options,
* IGP (Interchassis Ground Potential) and consequent hum.
As the philosophy which
I adopt seems to be different to what I read in these posts, I thought I'd set out
my philosophy re. - in particular - unbalanced systems and invite your critique as to what might be wrong with it.
Firstly, mains cords. IMO, unearthed, 2-core mains cables only exist for cost-saving reasons. If you wanna do it
right, then:
* the mains cord is 3-core
* whether it's a captive mains cord or you have an IEC chassis-socket, the earth wire/earth tag is connected to the (metal) case. This:
a) acts as "
safety earth", and
b) creates a shield against RFI for the signal processing going on inside the case.
Secondly, input & output RCA sockets. These are
always isolated from the case. IE. signal ground does not touch chassis - hence never touches mains earth.
Thirdly, unbalanced IC construction. Simple RCA-based ICs have the shield acting as as the 'ground' / 'signal return'. Given that the shield picks up RFI, what you automatically have is RFI noise being injected into signal ground at the destination RCA socket.
IMO, what is a better idea is to have an IC made up of 2 wires ('signal' and 'ground') enclosed by a shield which is connected to the
chassis at
one end only (source or destination - I don't think it matters).
Fourthly, signal ground ... as mentioned in 2, above, signal ground floats throughout the system; it
never connects to any chassis.
Fifthly, IGP. Yes, which way round the primary winding of the power transformer is connected to the mains makes a difference to the chassis ground potential ... and the sound of the component. (And the lower voltage reading gives the better sound.)
However, if you adopt the previous 4 articles of faith, it makes no difference to the level of hum.
Interested in your input, guys.
Regards,
Andy