Progress.

Ran a ground inside the amp from the star ground point to the screen pin
on the XLR7. Buzz now constant - and makes no difference if you get close
or touch anything.

X/0 was bolted to the speaker stand. Stand made of ally Speedframe, and
the joints (corners etc) are plastic covered so may well not make a good
electrical connection. Amp is just sitting on crossbars and has rubber
feet, so insulated.

Unbolting the X/O and just leaving it lying on top of the amp, clean.

Insulating the mounting between X/O and stand is going to need thought,
though. At the moment it's just a basic rack mount.

--
*The early bird gets the worm, but the second mouse gets the cheese *

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