AW: 2/4 quadrant multiplier theory

[Haible Juergen]

	>What is this circuit like? Is it an inverting amplifier with unity
gain where 
	>you connect one end of a pot to the input and the other to the
output? The 
	>wiper then outputs a signal that goes from 1 to -1 gain.
	>Or is it something more clever?

This is method #1, and it works fine, but it has no constant
output impedance.
Method #2 is building an opamp all pass stage, and replacing
the RC filter with a potentiometer.

JH.