AxeFX USB + Audio Interface = Ground Problem?

JazzMac251

Inspired
Hi all. I'm trying to get the most out of my AxeFX 2 setup. I was trying to figure out how I could achieve these things with my setup:

1) Use my Axe2 to interface with my DAW (Cubase 5) so I can easily record.
2) Interface the Axe2 with my computer via USB so I can still use Axe Edit to manipulate patches.
3) Use my PC speakers to monitor (I know, I'll get some powered monitors when I get a chance - my current 2.1 system isn't too bad, though), and do this with as little latency as possible
4) Use my Axe2 + PC as a practice amp when the Axe is home (i.e. not being used for digital-only gigs)
5) Do all of this with a minimum of cable-switching and fiddling with system properties

Here's the solution I came up with.

1) I interface the Axe with the PC via USB. This satisfies #1 and #2
2) To address the input/output latency issue, I installed ASIO4all, set it up to use the Axe as the input device, plugged Output 1 of the axe into the rear 1/4in INPUTS of a Focusrite Saffire Pro14 firewire audio interface I already had, plugged my PC speakers into the Focusrite box's monitoring Outputs, and set ASIO4all's Output device as the Focusrite box. The Saffire sums for monitoring all inputs and outputs in the box itself (without involving the PC directly), and this provides me with both PC audio AND 0-latency monitoring from the AxeFX. The recording latency is down to 2.6ms on both the output and input sides. This achieves #3 and #4.
3) Why not just use the Axe as a soundcard? Because in that setup the Axe has to either be on all the time to route PC audio, or I have to go through the hassle of resetting my default audio devices, crawling under my desk to get to my PC speakers and plugging them into the Axe whenever I want to record or practice. That is impractical. With this setup, all I have to do to record or practice is turn on my Axe. Much better!

Here's the problem:

I'm getting some wicked ground buzzing with the Axe's outs plugged into the Focusrite's ins. It's only on the Focusrite side, too. My recordings are dead quiet. Do I just need to get some Humbuster cables or what? What could be causing this issue?
 
There seems to be a charge building up on the guitar cable, too. Touching it send a loud pop through the unit and the speakers. The guitar cable is also highly microphonic. None of this is present when the Axe is NOT hooked up to the audio interface.
 
Is everything grounded properly?
Either way, have you tried using SPDIF?
If you use spdif you should still have the same setup.
 
what would that have to do with it? just curious as I use my macbook pro and have no issues
Becasue laptops that run off power "adaptors" (eg: 12v DC converters) are *NOTORIOUS* for causing/having ground loop buzz/hum for audio over USB. YMMV might vary with macbook.. not a Mac guy.
 
A fast way to know if its the adapter that is causing the problems is to unplug it and run on batteries for a short while. If the noise stops, it's the adapter.
 
After 6 hours of hunting for ground problems among all my gear, I finally opened up my Axe and found that 2 of the 3 pins on the header of the front panel instrument input had come unsoldered. took about 15-20 minutes to repair after I found the issue.

The contact pads on the PCB are extremely small. It was very difficult to repair the joint without burning the hell out of the PCB - which I ended up doing anyway. Oh well, at least it works now. :) It looks to me like there wasn't enough surface area on the contact pad to make a reliable joint so the original joint just popped off in 2 places.

I bought this item used here on the Fractal forums from someone that shall, for now at least, remain nameless and was given every assurance that the unit was in pristine condition. Kind of hard for me to believe that the owner didn't notice this massive ground issue with the main input pf the device... It was packed very well and the box showed no impact damage either, so I doubt this happened in transit. Hmph...
 
On a positive note, while I was inside the box I took note of what type of fan was in there. It seems to be your standard 80mm electronics fan. Should you find the stock fan annoyingly loud, this should be a far superior option: Noctua NF-R8 80mm Fan (31 CFM) - FrozenCPU.com

Here's a demo of it on youtube: Noctua NF-R8 PWM - YouTube

I don't start to hear any fan-whine until somewhere around 10 volts, which is very near to the fan running at max RPM. With the fan's included Ultra Low Noise adapter, you'll be running at far lower RPM than what you're hearing in that video at 10v and you'll be pumping out 15cfm, still higher than the stock fan's 14cfm.
 
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