In article ,
Sumatriptan wrote:
I'm now convinced it is stray field pickup due to the poor
quality, long phono leads. I tried 'shortening' the leads by wrapping
them into a small volume and the hum level reduced considerably. That
workaround plus the isolating transformer in the motor 50Hz feed has
given this result:

If it's hum pickup in the cables, you can usually prove this by moving
them, and see if it changes.

--
*He who laughs last, thinks slowest.

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