pedal switcher problem: hum when plugging in second amp!

[mainlymusicman]

i just wired up my 3 pedal switchers with comander.

im using the last loop of the 3rd pedal switcher to switch between amps (soldano and marshall, one set to clean, one set to dirty)

everything is fine when using just the soldano, but when i plug the cable going to the second amp into the OUT of the pedal switcher i get a bad hum coming from the soldano(the amp thats not selected)


its not that bad when the amp is turned down, but at the volume ill be using for a gig, it would be real loud..

it happens wether the guitar is plugged in or not.


i tried switching out the guitar cable, and i even tried powering the pedal switcher with its own power adapter in a separate outlet, no good.

i also tried a different pedal switcher... still the hum...

i tried plugging both amps into the same wall outlet, still hums...



anyone have any ideas??

i dont have much time to get this sorted out

[domct203]

Have you tried just a single pedal switcher with nothing but the two amps to see if anything changes? Just guitar, pedal switcher, amps.

Dom

[mainlymusicman]

Have you tried just a single pedal switcher with nothing but the two amps to see if anything changes? Just guitar, pedal switcher, amps.

Dom

yeah, i unplugged everything else from the pedal switcher. even the power of the pedal switcher.

and the hum is there on the first amp(soldano) even if its selected or not.

[mainlymusicman]

well i think i solved it, sort of...

just on a hunch, dont know why, i tried cutting the ground connection on one end of the guitar cable going to the marshall amp, and 80-90% of the hum was gone.

does this make sense?

id love to know why this worked, and why this hum is there to begin with. cause i have no idea... and maybe theres a better way to achieve the same result???



can anyone tell me if this is safe?

both amps still have their 3 prong power cables plugged into the outlets.

[JohnClark]

The hum is (was) a result of a ground loop. Once you lifted the audio ground to one of the amps, you eliminated the ground loop. Lifting ground on one of the audio cables, as you have done, or adding an isolation transformer before the front end of one amp are the two usual solution choices.

Good Luck!

[mainlymusicman]

The hum is (was) a result of a ground loop. Once you lifted the audio ground to one of the amps, you eliminated the ground loop. Lifting ground on one of the audio cables, as you have done, or adding an isolation transformer before the front end of one amp are the two usual solution choices.

Good Luck!

thanks john.. as an update ive since bought one of those EBTECH "hum X" plugs, which is to eliminate ground loop hums... i plugged the marshall amp into it and pluged it then directly to the wall, and bing! - hum completely disappeared!!

before, with cutting the ground on one of the cables, there was still a small amount of hum present, now theres zero!!

and ive gone back to using an unmodified cable to the amp, as i dont ned it anymore.

its more expensive , but it works.