Electronic sounding Hiss from Studio Monitors. Any Tips?

[Arktik83]

So I have a pair of KRK Rokit 5's, most recent models and I put them through my apogee Gio.

When music is playing they're fine, do the job they need to do but when idle they have this weird kind of electronic hiss, it can be rather annoying.

I've done a few processes of Elimination and it seems to be eminating from my Gio. I thought it might be drawing inteference from my mac because it's bus powered, no adaptor needed and when I plugged in my dad's M-Audio which has an adaptor there were no issues.

My flat has old wiring so I would say that the issue is generally coming from the power supplied to the unit but any work-arounds other than getting the flat re-wired or flogging the apogee?

Thanks!

[maltingsaudio]

Most likely coming from mac power supply is it a laptop?

[Arktik83]

Most likely coming from mac power supply is it a laptop?

Nope, it's an iMac.

[Arktik83]

Found the source, it's either the apogee or the USB from the iMac is giving it interference. Either way it seems like I'll have to get a new independtly powered interface. Bummer =/

[ecc83]

Is the noise present when just using headphones? If not you have a fairly common usb computer/earth/monitor loop problem and maybe Apogee can suggest a fix? Noisy usb returns are rather common on cheap 16bit usb mixers but you would expect state of art here?

I note the manual does not give a signal to noise figure (poor show Apogee. Not in keeping with your rep!) but since the device is 24bit capable I would expect a noise floor at~ -100dB FS? The output is also a rather puny +12dBu but even so, noise should be way below that.

Dave. No hint of a noise problem here: http://www.soundonsound.com/sos/jun1.../apogeegio.htm