Unbalanced output noise problem (static-like)

K

Kilvert

Member
Hey ... I just received my Ultra last Friday. I am experiencing a significant noise issue that seems to be emanating from the unbalanced stereo outputs.

I am using a simple PC recording set up right now. Here is how it is configured:

* Guitar> AXE front input> AXE unbalanced outs>Presonus Audiobox Inputs>Headphone Out from Audiobox

* I also have the Axe MIDI in and out properly connected to the Audiobox.

Everything functions perfectly but there is a very significant static-like/interference noise that I cannot seem to isolate. It is NOT present when I simply plug my guitar directly in the Audiobox. Interestingly, the noise persists even when the Axe is powered down.

Any advice would be GREATLY appreciated! Is it possible using the balanced outs would alleviate the noise/interference?

Thanks in advance!!
 
The crud on your signal could be coming from the Axe-FX, your guitar or cable, the Audibox, from a level mismatch between the Audiobox and the Axe-FX, or a ground loop between the two devices. The first step is to isolate where the noise/interference is coming from. Here are some things to check.
  1. Is the noise still there when you unplug your guitar cable from the Axe-FX?
  2. When the noise is there, can you reduce or eliminate it by turning up the threshold on the Axe-FX noise gate?
  3. Do you still get the noise when you plug your headphones directly into the Axe-FX output?
 
Thanks for the reply and suggestions.

Answers:
1) Yes. The noise is still there when the guitar and cable are removed from the input.
2) No. The noise gate doesn't seem to have any effect.
3) I have not tried to plug my headphones into either one of the unbalanced outputs. I will try that.
 
Update:

3) No. the noise is NOT present when I plug my headphones directly into the unbalanced outs. ;)

It doesn't sound like a "clipping" type of noise which might come from a level mismatch. It is more like a random high freq interference sound.

It is NOT affected at all by turning the out knob of the Axe to OFF. It also remains present when the Axe is completely powered down as long as the output cable remain plugged into the Axe.

It seems something is getting picked up at the unbalanced outputs, into the Audiobox and ultimately through the headphone amp of the Audiobox and the USB audio path to the computer.

If the unbalanced audio signal path between the Axe and Audiobox is removed it goes away.
 
That's a good start. From the first two tests, we know that the problem isn't being caused by the guitar or guitar cable. When you try the third test — plugging your headphones straight into the Axe-FX outputs — we'll know whether the Axe-FX is putting out a clean signal.

If you have a balanced XLR cable lying around, that's worth a try, too. Be sure to disconnect any unbalanced cables you may have on the Axe-FX output before you try the XLR cable.

One thing I noticed is that, from what I've read so far, the Audiobox takes an instrument-level input. The Axe-FX puts out a line level signal, which is way, way hotter than what the Audiobox wants to see. You may be overdriving the Audiobox. It may or may not be possible to fix that with the level controls.


Here's a summary of things to check next.
  1. Do you still get the noise when you plug your headphones directly into the Axe-FX output?
  2. Do you still get the noise when you turn the Axe-FX output level all the way down?
  3. Does the noise change when you play your guitar, or is it constant?
 
Hah! You beet me to the punch with your response.

We now know that the Axe-FX is outputting a clean signal. It's starting to smell like you may have a ground loop problem. Try the XLR cable and see what happens. You might also want to make sure the Audiobox's phantom power is turned off. I'm not sure whether or how that might affect the problem.
 
Thanks for helping Rex. Great info on the possible mismatch, I did NOT know that. I am travelling on biz right now and don't have access to my cable stash. I will try the XLR/balanced connections when I get home. I don't think it is an issue with the Axe.

1) No. See my post earlier.
2) Yes. Ditto.
3) No. The noise is constant and is not affected by the guitar signals.
 
I have double checked the phantom power and it doesn't seem to be a part of the issue. You are probably right about the ground loop thing. I will have to try and isolate some power sources. Also, do you think if I go with the XLR outs and lift the ground on those outputs it my work?
 
Try it both ways: with and without ground lift. By the way, phantom power only applies to the XLR input; it doesn't do anything on the 1/4" unbalanced input.

I'm curious — we've discussed the noise — are you getting any actual guitar sounds through the Audiobox?
 
Hey Rex ... YES! Everything operates perfectly. The Axe and my guitar sound incredible. The noise/interference is a constant and only affected in volume by the headphone volume control.

I don't think there is much else I can try until I return home. Who knows, maybe it is crappy rural hotel power/lighting that is causing it!

I will post the results of testing then.

Thanks again Rex!!!!
 
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Good luck! I'm looking forward to hearing that the problem is solved.
 
Update: My noise floor issues are entirely resolved. :) For anyone else who may be using a Presonus Audiobox a/d - midi interface, my friend Rex, in this thread, informed me that there is a signal level mismatch between the Axe unbalanced outs and the Audiobox unbalanced in's. This not only degraded the quality of the tone I was hearing but I have come to believe that the 1/4 in cable I was using for that turned into a 3 foot long antenna. :(

The resolve was to simply use the balanced outs on the Axe to the balanced in's on the Audiobox. The result is absolutely no ground floor noise at all.

I thought the Axe sounded amazing already BUT NOW? Un-Freaking-Real!

Thanks again Rex!
 
You're welcome! I'm glad you're running clean.

In truth, I think the level mismatch holds true for the Audiobox's XLR inputs as well, and that going balanced is what stoppped the three-foot-long antenna problem. In any case, it sounds like you've resolved any level issues with judicious use of level controls. If you hadn't, you'd know. :)

Enjoy!
 
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