On Thu, May 15, 2008 at 1:51 PM, Chuck Guzis <cclist at sydex.com> wrote:
A couple of weeks ago, I was working on a friend's
old Roland analog
synthesizer and discovered that there were *two* grounds on the thing-
-digital and analog. And they weren't the same. Neither one
corresponded to case ground or even the sleeve on the audio output
jacks. Fortunately, both grounds had labeled TPs on the PCBs.
Good and common design on synths. Ground loops can be a killer -
figuratively, not literally, introducing hard-to-remove hum on lines.
First time I saw a "ground lift" I was shocked (again, not literally)
by the concept, but found it indispensable for many live setups.
Was the connector on the audio a 3-conductor 1/4 inch? The analog
ground might be on the ring, not the sleeve. You plug in a mono 1/4
plug, it'll ground the sleeve, and a "stereo" (tip-ring-sleeve) plug
is usually used for balanced signals - the analog ground becoming the
-ve line. The sleeve can connect to the cable shield on either side
in that case, and sometimes this is a must - it's useful to have one
or two balanced 1/4 phono cables with sleeve to shield on only one end
in your box o' cables!
Ideally (but expensive) there should be and isolating transformer on
the output. And 3-pin XLR.
Joe.