Laney VC30 valve amp, works fine in its own accord. But owner wants to set
it up with another amp , another make and solid state if relevant, for a
pseudo stereo set up using the A and B outputs of a pedal effects unit.
Produces mains hum on switching from standby to on. Making one of the feeds
isolated and relying on the grounds from each amp makes no difference, still
intrusive hum.
Bridging stout wire from mains earth to the VC30 input socket makes no
difference .
Pulling V1 from the amp still induces hum in the other amp. Had to return
the amp for owner to do a gig as normal mono set up. I did not try an
isolation transformer and I did not get inside the works, just testing the
valves. I'm assuming internal shared ground path for HT return current ,
anyone any thoughts for the next time if I'm faced with this.
Only a year old so maybe PbF problem at the input perhaps

less than 0.1 ohm between input ground and mains ground in all 3 cases of
the VC30 , his other amp and my amp to confirm a VC30 problem

On Thu, 29 Sep 2011 10:03:30 +0100, "N_Cook" wrote:

less than 0.1 ohm between input ground and mains ground in all 3 cases of
the VC30 , his other amp and my amp to confirm a VC30 problem


Is one side of line bonded to ground where you are? If so there may be an
incorrect bonding or lack thereof.

??-)