Diagnosing hum/static with AX8 rig

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FarmerTodd

Member
I've noticed over the past few weeks a persistent hum/static sound coming from my rig. I've not had any luck in isolating the cause; I've changed just about everything other than the AX8. The sound is clearly gated; the unit is dead silent when not playing. When I pick very lightly, though, I can very clearly hear the noise. As soon as the note dies, the static also dies. Likewise, a tremolo will cause the volume of the hum to rise and fall, along with the guitar signal. I'm therefore working on the assumption that the source is somewhere in the guitar -> AX8 path (not AX8 -> speaker path). This is with all patches - not just a single one. It's most easily observed with clean settings, of course.

While this is most acutely noticed with single-coil passive pickups, I can hear the same static sound with my EMG-SA active pickups, my Seth Lover humbuckers, and in all pickup configurations. I've tried different cables, as well as a wireless unit between guitar and AX8 - all produce the same result.

I've tried different physical environments to see if that was a significant factor - I notice no difference. My primary space is my home office, and there are multiple computers and other electrical devices. I've tried turning off/disconnecting all of those electronics, but there's no meaningful difference in the noise.

Any suggestions on next steps to diagnose the problem? I can't say for certain that this is a new development, but it's certainly something I had not noticed until about 1-2 months ago.
 
I'll also add that the unit isn't clipping - the passive single coils barely register yellow, much less red, when strumming hard. Pad is set to 0db.
 
Post a recording and an example preset that demonstrates the problem.

Also, set your input pad to 0dB. Noise better or worse?

Edit: nvm about the pad then. Hmm. But do please post a recording.
 
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Here's a recording. I used the settings which result in the most pronounced sound - Classic Vibe Telecaster, bridge pickup only. There is definitely a ground issue going on with this guitar - touching the strings significantly reduces the noise, but not entirely. There are other guitars which exhibit the same sound, but don't have any obvious ground issues. For example, I have an old Variax 300, running on a 9v battery (not power over cable) that has the same static sound, but no change in behavior depending on whether my hands are on the strings or not (and since the sound from the Variax is a product of the digital modeler and not the pickups directly, this makes sense to me).

The patch used here is a very lightly modified version of the factory Vibrato-King preset (delay and trem tempo and mixes changed, output leveled to ~0db using the VUs).

The first note has me not touching the strings or any metal. The second shows the sound when I'm touching the strings at the same time.

I can record other combinations of guitars and/or cables as needed.
 
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FarmerTodd said:
I'll also add that the unit isn't clipping - the passive single coils barely register yellow, much less red, when strumming hard. Pad is set to 0db.
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I have a friend who I sold my AXE FX2 Mark2 to. He has noise problems caused by his computer. Not sure if this is your problem.
 
In that same preset you used for the recording, completely disable the input noise gate and any gate/expander blocks. At that point, the only change in noise you should hear when touching/releasing the strings is ground loop related. There is most certainly a gate in your preset clamping down the noise in the middle of the recording.

I heard a sweep in the static on the second note, which points to EMI, especially from a computer processor - was your USB cable plugged in when doing this recording? Also note that some recording interfaces are susceptible to this noise as well. Have you tried plugging the AX8 directly into a speaker or headphone amp with no computers? Does the noise get worse when doing things on the computer (making the CPI work harder)? Does it get worse when moving the LED knobs on the AX8?

If you manage to deduce that the sweep noise was generated from the AX8 itself, then I'd recommend contacting Fractal support. That could indicate the AX8 processor is bleeding EMI into the signal before the AD converter.

Another thing to check is gain staging. Some level of noise is to be expected with all equipment. Properly setting your gain stages for optimal signal to noise ratio is important. So - Output 1 on the AX8 should be as high as your interface or speaker input can handle before clipping. If your interface supports +4dBu line level, use that; if it's a mic preamp, turn the mic preamp all the way down and use the AX8's output (as it is hot). In my home studio setup with an Apogee interface, I get a ton of ground loop noise from the XLRs when the inputs are set to Mic and connected to the AX8, but as soon as I switch to line it is transparent.
 
Thanks for the feedback. The recording was generated with CV Tele -> AX8 -> M-Audio Fast Track Pro -> Reaper (PC via USB). The noise in the recording is consistent with the noise I get plugging the AX8 directly into the powered monitor, or directly into the house mixer (with no computers present). With the CV Tele, positioning the pickups facing the computer makes it worse (as expected), but other guitars (e.g., Variax) have no meaningful difference (but slightly lower levels of noise).

I also heard the sweep, and I'm guessing that's from the computer as well. I wouldn't say the sweep is representative of the problem I'm facing, though it may be related.

I'll try to make another recording later today after making the changes you suggest. I'll grab include both the CV Tele and a different guitar (that seems to not have the same grounding issues) as well.
 
The USB I used has one choke - should I expect that to suffice?

It's worth noting that the USB was only in use to generate the recording - the same noise (minus the sweep) is present without any computer present.
 
If the gate is killing the noise, it is coming from the input. Your guitar pickups or cable is likely picking up interference from something environmental. Move to a different spot in the room or to a different room and see if the noise changes.
 
Yes, definitely your guitar picking up interferences, try to go as far as possible from PCs and neon lights and check your guitars' shielding
 
I've tried something like 8 different guitars, 3 different cables (plus one wireless system), three different locations in all sorts of combinations - all produce the same static-like noise. That's what's got me confused. I've tried pretty hard to isolate it to a component other than the AX8, but everything I try has the same problem. I'll dig out my tube amp tonight and see what happens when I plug straight into that.
 
FarmerTodd said:
I've tried something like 8 different guitars, 3 different cables (plus one wireless system), three different locations in all sorts of combinations - all produce the same static-like noise. That's what's got me confused. I've tried pretty hard to isolate it to a component other than the AX8, but everything I try has the same problem. I'll dig out my tube amp tonight and see what happens when I plug straight into that.
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Yeah but as Mr_fender wrote, if it goes away with the noise gate it's coming into the ax8 thru the input, so the noise is coming from outside the ax8 or (very unlikely imho) a faulty input stage or AD converter in the ax8. To exclude the latter try to connect into input 2 and see if it goes away.

Ps: in your sample I hear basically the same noise I get when standing in front of my PC monitor

Pps: now that I think about it something similar could happen if the ground connection on the input jack of the ax8 is not properly soldered, in this case the noise should go away by using input 2. If that's the case contact support
 
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So, the only gate on that patch is the global input gate. How would I turn that off? I can adjust threshold, ratio, attack, release and level, but I don't immediately see an option to fully disable the gate.
 
FarmerTodd said:
So, the only gate on that patch is the global input gate. How would I turn that off? I can adjust threshold, ratio, attack, release and level, but I don't immediately see an option to fully disable the gate.
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Turn down to minimum threshold or ratio
 
Thanks for all the help so far - some interesting developments.

First, I reduced both threshold and ratio for the input gate down to minimum values. The result was that the static was no longer gated, and could be heard clearly without any playing.

I then modified the patch to use Input 2 (via an FX loop block), connected guitars to that, and heard the same sounds (so, does not seem specific to Instrument In).

While unplugging and plugging things back in, though, I noticed something strange. With the gate set to settings allowing the noise without playing, the noise could be clearly heard (modulated by the enabled vibrato) with nothing plugged into any inputs (Instrument In or In 2). I made a quick recording to show that:



I'm including the test patch used, just to sanity check that I didn't do something strange with the FX loop to cause this (I don't use FX loop at all, and have never previously used any input other than Instrument In).

The static I hear with no input connected at all is the sound I'm trying to eliminate. There are also environmental issues, and guitar ground issues, but I think this recording pretty well demonstrates the bulk of my problem - without any guitar or input connected. Is this a valid test, or am I doing something that's introducing this noise even when no inputs are connected?
 

Attachments

  • Static Test.syx
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I'll note that I've also used multiple cables between the AX8 output and speakers/Fast Track Pro, all with the same result. I've tried both normal 1/4" as well as TRS 1/4". I don't have Humbuckers to try, but given the trem modulation, it seems unlikely that the output cable is the source of the noise.
 
I was getting a lot of static and noise and was ready to replace cables and go crazy. I moved my AX8 to a different part of my room away from a TV and it stopped.
 
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