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Annoying Hum

In my recording (DAW - Adobe Audition 2.0) I am using an Alesis Fusion 6 HD synthesizer going into a Phonic 12 Firewire Mixer, and then into my computer with a firewire cable. (Windows XP). The problem I am experiencing is an audible hum whenever I hook up the Fusion to the mixer. I get it on every channel. I don't get it when using a microphone for voice and guitar, and I don't get it when I play the Fusion by itself, not hooked up, using headphones to listen.
The sound card is a Sound Blaster Audigy, which comes with a hub. I tried disconnecting the hub and went firewire direct into the PC, and still get the hum. According to the device manager, the sound card drivers are working fine. Any other music I listen to is fine, CD or mp3 or streamed. The Phonic drivers are used for recording and the Audigy drivers are used for playback.
I tried switching cables and tried various hookups. I normally run a cable from the Fusion Headphone jack to the mixer channel, but have also tried the left and right channels out of the Fusion as well.
Anyone have any suggestions? (I hope I posted this in the right place. if not...sorry)


Boswell Mon, 07/10/2006 - 02:39
Do you get the hum when the Fusion is connected to the mixer and to the mains but switched off? If so, does the hum go away when you unplug the Fusion from the mains?

What happens if you connect the Fusion L and R outputs to the Audigy soundcard inputs (by-passing the FireWire mixer)? You will have to enable the Audigy drivers for recording instead of the Phonic drivers for this test.

What type of cables are you using to connect the Fusion to the mixer (balanced TRS, unbalanced TS etc)?

I'm not 100% clear about how you normally connect the gear together. When you plug into the headphone output of the Fusion, do you use a split lead to feed two channels of the mixer?

Member Wed, 07/12/2006 - 07:17
Thanks for the replies. I have determined that the problem is a ground (earth) loop. I plugged in a Direct Box with a ground loop switch, even using mono cables, and that solved the problem. No hum at all. Previously I had tried hooking up with TRS cables and there was still some noticeable hum.
In answer to your question about hookup, I originally ran a mono cable out from the keyboard headphone jack when I'd read someone's blog that they'd gotten good recording results that way. Since then I've learned that not only is the headphone signal more amplified but it is also unbalanced so now I am running cable from the keyboard L & R out to the Mixer stereo L & R in. Then the mixer runs to the PC through FireWire.
En route to all this I did try rearranging my power supply, having everything coming from the same recepticle source, different combinations of wire et al, and still the hum was present. It was only the Direct box that stopped it. So...that's it! Problem solved. Yay!