Reducing Interference Hum


Hi all

I was wondering if someone could explain to me what is happening with this interference and how I might go about decreasing it. Any suggestions on how I might improve setup overall would also be appreciated.

I have an instrument lead unplugged and there is an audible hum in my headphones (HD-25) when i point the lead at the monitor of my iMac it stops dead also the external hard drive boxes, the 003 rack and the speaker amp. Gets louder and pitch changes when i point at my Roland electronic drums- switched off and changes pitch when i point at the modem/ voip phone. I have used another lead to check it wasn't that.

When i attach the lead to my acoustic guitar (maton with AP5 active pickup) it still hums away at roughly the same volume and pitch. Which is the annoying thing I would like to decrease hum on.

i have turned everything off except the preamp and monitor and still get the hum. Running an Apogee Mini-Me into a 003 rack via spdif cable.

Since above post I've done a bit more homework and it would appear that ground loop is not as bad as first thought. However the unbalanced instrument cable I am using for my guitar is still very annoyingly noisy. Any tips on how I can reduce hum on the unbalanced cable to recording interface?


Looked at a few sites and a suggestion is to disconnect the shield in one end!

Used an active DI with no improvement in the hum situation.

Been a good exercise in cleaning up my leads, connectors etc


Why does hum disappear when I touch the sleeve? How can I replicate this in the path from my guitar to computer?