A shockingly basic question

Dan Higdon hdan at charybdis.com
Thu Jun 26 21:13:50 CEST 1997

This is a shockingly basic question :-), but for some reason it
occurred to me the other night, and I couldn't answer it.

If you have a 1/4" jack input (2 conductor), the normal way to
hook it up to an opamp is to ground the sleeve, and then tie
the tip to the opamp in with a resistor.  However, this causes
your module to share ground with the incoming signal, which
(I think) could cause a ground loop, especially if both devices
have ground pins on their power cords.  Am I right so far?

Ok, here's the question:  Assuming you're just doing something simple
(like buffering the signal), could you hook it up as follows:

          | |\   |
TIP: --R1-|-|-\  |
            |  \_|___ Out
            |  /

This would (I think) accurately buffer the signal (inverted, of course), but
without a ground connection between the two devices.
Am I right?  Is this a pointless observation?  Thanks for any responses.

I'm slightly embarassed, since I've been building modules for a little while
now, and I routinely redesign the schematics floating around to better match
my requirements.  Oh well, the hazards of an informal education....

Dan Higdon (hdan at charybdis.com)

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