Hum using usb fast track but no hum when using headphone output.

[pslater]

Hi all,

I'm installing a small Mac suite at the moment and bought Fast Track audio interfaces as I thought these would ensure a reliable, clean audio signal. However, after much investigation with cabling etc. plus quite a lot of googling into ground loops and the like, I have discovered that if I just use the headphone output from the iMac, the signal if free from any unwanted noise. Has anyone experienced this before? I'm sure it's going to be down to the power for the fast Track going through the same USB as the data and have also tried putting a powered usb hub in-between the Mac and the Fast Track in the hope that the Fast track doesn't get its power from the Mac, but this hasn't helped. I should also mention that the unwanted noise isnt just mains hum, it has a higher pitch to it too and includes random clicks and pops...oh and I've got the latest drivers for the Fast Track too!

Mant thanks,

Pete

[mbrunt]

If plugging a set of headphones into the headphone jack of the mac is totally fine but going via the USB Fast Track isn't ok then its fairly obvious its the Fast Track at fault. Does the fast track require power from mains? If so, try moving to another socket. What happens when you plug an input into the fast track, but mute that input, is the hum still there? What about when you plug an input into the fasttrack and play sound (e.g.) a guitar, is the hum still there?

THanks

[mbrunt]

Have you also tried removing the fast track, taking it to your office and plugging it into your pc?

[pslater]

The fast Track can only be powered through USB, will try the input idea. This problem occurs for all 10 of the Macs and Fast Tracks that I have installed.

Pete

[j17sparky]

Using what software? Is the latency set too low? Is there hum/noise when no applications are open?

[Andrew_C]

The hum will probably be a ground loop issue. Happens a lot with sound kit. Quickest fix is an isolating transformer, about the cheapest I've seen are the in-car ones that CPC sell.

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