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<div class="moz-cite-prefix">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).<br>
<br>
On 05/01/2014 02:46 PM, Jeffrey Crews wrote:<br>
</div>
<blockquote
cite="mid:CAJ8-eyEtiEisLcs8FfynEdz56F3OpLosYh+XdpL=GUYqQwaH7A@mail.gmail.com"
type="cite">
<div class="gmail_quote">Apropos of nothing, the same issue arises
in guitar wiring; you can get hum if you have ground loops.
<div><br>
</div>
On Thu, May 1, 2014 at 2:29 PM, Martin Brooke <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:martin.brooke@duke.edu"
target="_blank">martin.brooke@duke.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_extra"><br>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">The
problem arises when you use the resistors R1 and R2 to
support a higher output voltage.</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">
<br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">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.</div>
<br>
</div>
</div>
</blockquote>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="80">--
Scott G. Hall
Raleigh, NC, USA
<a class="moz-txt-link-abbreviated" href="mailto:ScottGHall1@GMail.Com">ScottGHall1@GMail.Com</a>
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