Been playing with an pro electronic crossover in conjunction with a Quad
405, and am having ground loop problems.

IIRC, a 405 used with a 33 etc pre-amp doesn't have the mains ground
connected - it gets its mains feed from the preamp via a two core main
lead. Perhaps not PC these days. The 405 input socket has the ground
connected to chassis. Have read the grounding arrangements internal to the
405 are slightly odd. ;-)

The crossover has electronically balance outputs, and the manual shows how
to connect them as unbalanced - the normal way of linking XLR pins 1&3 as
screen, and therefore ground at the 405.

With that done and a mains ground to both units, a ground loop. No
surprise.

With the mains ground lifted from the 405, better, but still slight hum.

Unplug either lead from the crossover - perfect.

Remove the ground connection from one lead - at either end - and there is
a slight buzz on that channel, the other staying perfect. I've been
experimenting with low value resistors in that screen - about 10 ohms -
which improves matters but still not perfect.

I'm running out of ideas. ;-) The connection leads are only about 1 foot
long.

Mains are two leads to a mains splitter. If I get things working properly
I may add a looped straight through IEC outlet to the crossover to tidy up
the mains wiring.

--
*Whatever kind of look you were going for, you missed.

Dave Plowman London SW
To e-mail, change noise into sound.