[TriEmbed] Ground Confusion

[Scott Hall]

That's why in pro-audio you ground only one side of all signal connections: in
broadcasting the rule of thumb is to connect grounds on the source side of the
signal only; in sound reinforcement or PA systems (live stage audio) its just
the opposite -- the rule of thumb is to connect the grounds only on the
destination side (this is to have the outside of most of the signal wiring at
the mixing console's voltage potential, and thus supposedly safer if one of the
instruments attends mains voltage level from worn-out stage amps and equipment,
and someone steps on a frayed outer jacket of a worn wire -- sounds awfully
dangerous to me though, if a guitar is plugged into an old tube amp where the
practice was to ground the chassis to one side of the 2-prong plug, and the
player steps on a frayed mic wire with his body as the ground path; I'd much
rather use a separate mic to the amps speaker, or at least a direct box
(non-galvanic line transformer, turns ratio 54:1 to reduce any inducted voltage
54 times) with the added bonus of giving me a balanced differential signal for
the long run back to the board).

On 05/01/2014 02:46 PM, Jeffrey Crews wrote:
> Apropos of nothing, the same issue arises in guitar wiring; you can get hum if
> you have ground loops.
>
> On Thu, May 1, 2014 at 2:29 PM, Martin Brooke <martin.brooke at duke.edu
> <mailto:martin.brooke at duke.edu>> wrote:
>
>
>     The problem arises when you use the resistors R1 and R2 to support a
>     higher output voltage.
>
>     If the ground on Resistor R2 (see page 12 of the data sheet) is not very
>     close to pin 9 you could get small voltages due to current in the ground
>     paths making your circuit behave unexpectedly.
>

-- 
Scott G. Hall
Raleigh, NC, USA
ScottGHall1 at GMail.Com

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