AW: AW: AW: To earth, or not to earth...

[Haible Juergen]

	>The balanced output stage is indeed a problem.  A common
solution is the cross coupled Howland >current source,  Like 
	>everything active it relies on good resistor matching for a
good CMRR.  A British broadcast mixer >manufacturer uses this 
	>topology with off the shelf sil resistor packs for the
"matched" resistors.  The brochure claims >ZERO output impeadance for 
	>the circuit (can't work as the op-amps are 553X which won't
drive 600R too well)..

Hi Tim,

Howland current source - I guess this is the word for things like the
SSM2142.

I'd love to see a design that uses discrete opamps (matched resistors
are no problem for me). I know the 2142 data sheet has a block diagram,
but I think there's more than just building the resistors around the
opamps
to get a circuit that is stable and protected under all output
conditions
(long cables). So I'd be glad to see a 5534 (or whatever) based circuit
from an existing mixing console. 

JH