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Excessive Amp Noise With HD500X (Video Clip)

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Hi all. Weird issue here -- I have a newer HD500X and when I plug it into my Mesa Single Rec half stack, I get a crazy loud pulsing buzz. 

  • Works great when I run the same line out to my audio interface
  • This buzz happens whether the line 6 has power or not, and with all cables or just the line out plugged into the amp input (both L & R).
  • I tried multiple cable brands/lengths, all the way down to 5'.
  • I tried different pedals and had no issues.
  • I tried flipping the physical switches on the HD.
  • I tried multiple outlets in the house on different breakers. The house is newer and we've never had electricity flow issues.
  • Unfortunately I don't have any other amps to try, but I can always run down to the local Music Go Round if it comes down to it.

I've been running live multi-effects setups with amps for years and never experienced anything like this. Video clip below. Anyone have any suggestions?

 

https://www.youtube.com/watch?v=7R3fIg1iJDc

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So, in that video, if you unplug the 1/4 inch cable from the POD, with the other end still plugged into the Mesa, the noise goes away?

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So, in that video, if you unplug the 1/4 inch cable from the POD, with the other end still plugged into the Mesa, the noise goes away?

 

Yep.

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Very bizarre indeed. I would think it would be just the opposite, i.e., noise in the amp from a patch cable plugged into the amp that is not plugged into a guitar at the other end.

 

I can't imagine what circuitry in the POD (which is not even plugged in) that could place any stress or information into the 1/4 inch jack, but the Mesa manual does make mention of "Noise can be in the form of crackling, sputtering, white noise/hiss and/or hum" with "mildly shorted tubes". I'm grabbing at straws but, have you tried going through the tube diagnostic procedures in the Mesa's manual? Couldn't hurt to see if everything is up to snuff in the Mesa.

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Could it be the metal plug cover on the 1/4 cable touching the metal R jack like I see in the video causing it?

 

I noticed that too, but wouldn't that be grounding a ground to ground? Plus he said he has tried a number of different patch cables. I don't know, maybe you have hit it on the head.

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First, thanks for jumping on this guys.

 

Could it be the metal plug cover on the 1/4 cable touching the metal R jack like I see in the video causing it?

 

I SO wish it were that simple. I've tried many cable types and brands.

 

Very bizarre indeed. I would think it would be just the opposite, i.e., noise in the amp from a patch cable plugged into the amp that is not plugged into a guitar at the other end.

 

I can't imagine what circuitry in the POD (which is not even plugged in) that could place any stress or information into the 1/4 inch jack, but the Mesa manual does make mention of "Noise can be in the form of crackling, sputtering, white noise/hiss and/or hum" with "mildly shorted tubes". I'm grabbing at straws but, have you tried going through the tube diagnostic procedures in the Mesa's manual? Couldn't hurt to see if everything is up to snuff in the Mesa.

 

Seems like the issues wouldn't be specific to the POD if that were the case, but I will check out the tubes. Thanks for the pointer. 

 

 

I noticed that too, but wouldn't that be grounding a ground to ground? Plus he said he has tried a number of different patch cables. I don't know, maybe you have hit it on the head.

 

Yeah, several cables -- shielded & not, angled and straight, long and short.

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That is a weird one. When you unplug the cable from the the Pod that sound goes away completely?

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That is a weird one. When you unplug the cable from the the Pod that sound goes away completely?

 

Yes. I'm gonna take the HD to a local shop and hook it up to another amp and see what happens. Other than that, I'm at a loss, short of just opening up the HD to see if something is visually wrong (which I doubt. it's newer and has been babied).

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It sounds like motorboating, which can be caused by a bad tube(s) or power supply cap in the amp. As to why the HD500 makes the amp do this the only thing I can think of is the output impedance of the HD500 (which is there regardless if the HD500 is on or off) is way different than a guitar. Maybe way different than pedals, too, although I can't find any specs on this. It may be interacting with the first stage of the amp in a way that makes this happen. Plugging the HD500 into another amp is a great test. But I bet it's an issue with the amp, not the HD500.

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pfsmith0 -- thanks a ton for the guidance. Ironically the Mesa head is the only thing in my entire gear collection that I bought used, so I guess it would be no surprise if the tubes were done for. ...and if that's not the case, new tubes won't hurt anything but the wallet.

 

Thanks again.

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I pulled my tubes and found a 12ax7 that is rattling. I'm gonna go grab a junk replacement and swap out to see what happens. Stay tuned.

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The plot thickens.

 

I replaced the tube. Didn't help. I lightly tapped on each of the 12ax7's -- On V1, I could hear the tapping through the speakers like it was a microphone. I could hear V2 and V3 faintly. I've read that if a tube is that microphonic, something is wrong. I tried switching tubes around...same issue.

 

Also, the sound is now faintly coming through even when NOT connected to the pedal, which leads me to think that the problem is getting worse the longer the amp is run.

 

Either way, looks like I have to track down an amp specialist (unless you guys have any other ideas). Unfortunate end to a weird situation, but thanks again for the pointers everyone. 

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First, let me just say... UUUUUUUUGGGGGHHHHHHHH. Still not fixed.

 

Now that that's out of the way, here's what went down. Took my amp to a repair shop and they found problems that they were able to fix. ALL weird amp noise is totally gone now when I plug my guitar straight in.

 

However, the original issue still exists (see first post) in exactly the same way. I tried all of the same tests and more. I also tested the pedal on a small combo amp and didn't hear anything unusual. I'm borrowing another amp tonight to test again.

 

Unless you guys have any other suggestions, I'm thinking it might be time to call Line 6.

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I am not telling you not to call L6. 

But, if the L6 doesn't do it with the other gear, I am not sure what L6 is going to be able to do about it.

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I am not telling you not to call L6. 

But, if the L6 doesn't do it with the other gear, I am not sure what L6 is going to be able to do about it.

I'm not saying it's L6's problem...I'm just trying to get information at this point.  Tracking down the root cause may be a process that requires me going back and forth between L6 and my amp guy a few times. 

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Wow that is crazy. But if the small combo isn't picking it up the HD is probably good.

 

I wonder if the HD (or something nearby) is cranking out some RF and your tube amp (or HD) is picking it up. A real long cable with the HD a good distance away would tell that one.

 

All guessing tough.

 

-B

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Did you try using the amp at the repair shop with the HD? Or somewhere besides your house? 

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Wow that is crazy. But if the small combo isn't picking it up the HD is probably good.

 

I wonder if the HD (or something nearby) is cranking out some RF and your tube amp (or HD) is picking it up. A real long cable with the HD a good distance away would tell that one.

 

All guessing tough.

 

-B

You might be on to something. I'm definitely picking up some other funny noises/radio stations/etc along with the motorboating. I'll report it to my amp guy.

 

 

Did you try using the amp at the repair shop with the HD? Or somewhere besides your house? 

 

Amp at the repair shop -- no. Amp in other physical locations -- yes, but not since I've gotten it back. Definitely something I'll check.

 

Plug the HD500 into the FX return of the Mesa and see if the noise is gone.

 

No noise when I do this.

 

After some more testing, this has to still be an amp problem. The HD causes the noise more than anything else, but I do hear it very faintly with the amp turned up very loud without the pedal. Guess it's back to the amp guy and maybe L6 to get some info on what about the circuitry might be setting it off so bad. Thanks everyone. If I ever figure this out, I'll let you know.

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May be that something in the amp is getting some RF from somewhere close.   I had a similar problem that was happening with a Fender head, in my home studio setting, and it turned out that the major problem came from 1 of 4 CFL bulbs I had in there for lighting..  That was tested by turning the lights on and off, one at a time.  How a bulb that was 7 feet away could cause an amp head to pick up a gospel radio station is beyond me, but that was what the deal was.  Changed out the bulb for a LED bulb, and now there is no problem.  Doesn't matter if you are running shielded cabling or not.  You may also be close to things in your neighborhood that put out a lot of RF.  Ham operators, big power company transformers, etc.. 

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