> A side question: No one has ever been able to explain to me why the third
> terminal (ground) is necessary.

That's because your brain has made the leap straight to the "A-B"
part. In order to determine what the answer to A-B is, you need to
determine values for A and B and they are both voltages with
reference to ground. You might be able to put your meter directly
across the terminals but an amp can't. It needs to get its power from
somewhere and do the sums with respect to ground.

Steve.



======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: steveb@tla.co.nz      fax +64 9 820-1929
======================================================

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