amp hum

[mark rachelle]

here is the situation

ui am running two different amps for my keyboard rig

out of the left side i am using a jc120 and on the right side a be!@#$%^& 90watt keyboard amp

all leads are good and both are off the same circut and power board

why would i be getting hum it happens to either amp

[Simon B]

I hope this isnt an insult to your inteligence..... but could it be an earh loop from using different power points? or an impedence mismatch?

[mark rachelle]

"all leads are good and both are off the same circut and power board "

including the keyboard
if i plug in the keyboard (a nord stage 88b) into either amp by itself there is no problem with hum

its just a rounder fuller sound with the two amps together

however tghe hum only becomes a problem
when 2 amps are conected to the keyboard at the one time

amp 1 is connected to the left output
amp 2 is connected to the right output

its not a huge problem but its one of those nasty inbetween earth hums

[Linear]

The hum comes from a potential difference equalising itself down the audio cables.

Try connecting the chassis of the amps together with some heavy duty cable. Also check that the amps themselves are properly earthed - sometimes 0V on the amp isn't connected to ground, making it a floating 0V (rob correct me if i'm wrong).

If you're feeling really techy, check 0V vs ground on the amp using a multimeter - make sure there is no potential difference there.

Chris