MXR ISO Brick - Ground Loop?

MSN0001

Today I upgraded my Boss BCB60 power supply to an MXR ISO Brick. The ISO Brick is silent when powered, all good so far. I am using a standard UK double switched power socket outlet which is earthed correctly and I've setup in the best place in my home that gives me the least interference, just the usual single coil hum through my Blues Jnr.

When I touch the powered ISO brick unit I get an audible buzz through my speaker. Is this due to the unit being earthed through the power socket and then earthed through myself when I touch it - is this like making a ground loop? Or is my unit faulty? 

Secondly, (not talking about the ISO Brick now, but with just my Fender Strat plugged into my Blues Jnr) the hum noise I'm used to is noticeably reduced when I touch the strings/bridge. Does this mean the ground connections in my guitar electrics are not grounded effectively? I always thought that a well grounded circuit in my guitar would mean no change in noise when touching the metal parts of my guitar.

thanks for your help - first post.

peteri

Ok - second point first, no that's normal - you're earthing the guitar, that's one of the reasons people talk about wireless as a good idea in dodgy clubs, saves electrocution.

No sure on the ISO brick, but my experience with one is it's less 'ISO' than the name implies, I had a pedal with a noisy clock which was audible through other pedals - which kind of makes you think there's not an entirely isolated signal.

Much happier with the (much more expensive) Gigrig stuff (there are cheaper alternatives)

MSN0001

Thanks for the feedback. I previously used the PSU on my boss BCB60 with a daisy chain setup, one of the capacitors was leaking electrolyte so I thought it was a good time to switch to an isolated supply and went for the MXR ISO because the variety of power options works well for my board. 

I powered the unit again today and tested all of my pedals one at a time with different power connectors and patch cables. I tried as many combinations and still I can't get rid of the buzz when I touch the power supply unit. Got 2 new mogami gold leads coming and if that doesn't cure it I don't know what else to try. 

Sporky

peteri said:

Ok - second point first, no that's normal - you're earthing the guitar

No - you're being grounded through the guitar, and your body (which is not far off a big bag of salty water) acts as a shield.

MSN0001

So it could be that when I touch the power supply I am creating another path to ground - resulting in a ground loop? Would this cause the buzz? The thing is none of my pedals react to my touch in this way so I'm leaning toward the idea that the ISO unit has a defect.