• From: Cardiff, UK
  • Registered: 2009-05-09
  • Posts: 28

Topic: [FF400] Ground loop when USB audio device connected to Fireface

I am experiencing a ground loop when connecting a USB-powered audio interface (specifically an MBox2 Micro) to the inputs of the Fireface 400.

The MBox2 is connected to the Fireface via a stereo mini jack to two mono jacks cable. The Fireface and MBox are both bus powered.

In an effort to break the ground loop, I've disconnected everything inessential from the PC, so that its only connection to the outside world is a single power lead. (I even unplugged the monitor.) The ground loop remains exactly the same.

Would using a different cable to connect the MBox to the Fireface help? Or is the problem something to do with the wiring in the PC? (Sorry for the dummies' phrasing - I can't figure this out...)

Thanks in advance for any advice.

iain_m's Website

  • From: Cardiff, UK
  • Registered: 2009-05-09
  • Posts: 28

Re: [FF400] Ground loop when USB audio device connected to Fireface

Sorry for the self-bump, but ... can anyone advise?

iain_m's Website

  • Registered: 2008-01-01
  • Posts: 3,025

Re: [FF400] Ground loop when USB audio device connected to Fireface

The problem might be that your USB port and Firewire port use different grounds on the computer.

When you say that the only connection is the power lead of the computer, what about powered speaker connected to the MBox or FF?

  • From: Cardiff, UK
  • Registered: 2009-05-09
  • Posts: 28

Re: [FF400] Ground loop when USB audio device connected to Fireface

Hey - thanks for the reply.

I disconnected the speakers (from both the audio interface and the mains) and monitored the levels using TotalMix (I can "see" the ground loop as a rise in noise on the input channels to which the MBox is connected).

Regarding the grounding of the firewire and USB ports, what you say makes sense to me in principle, but wouldn't they both ultimately be grounded through the single mains power line connected to the PC? neutral

iain_m's Website