Massive hum with XLR out into PA with my Tech 21 TM60

[AtomHeartMother]

I'm getting massive hum when using the Sansamp XLR out into the PA system, and it has both me and the sound engineer boggled. This is with both the ground lift button in and out (although it's slightly less apparent with it in). Here's the situation:

 

To begin with the most boggling thing is that the amp seems to work fine into the PA via the Sansamp out for a while. I had it connected and working great for the hour practice before the performance and then about another hour into the performance (we sporadically played about four songs during the course of that second hour). But as soon as I touched the guitar the next time we played a song, the massive hum started. They had to cut me out of the PA for the rest of the performance.

 

After the performance, the sound engineer and tried to diagnose the hum the best we could. The really strange thing is that there is massive hum even when the amp is turned off, as long as it's still connected to the outlet. The hum also comes through the amp; I can feel the speaker vibrating even when not playing anything. We tried several different outlets on several different circuits (many circuits were installed just a year ago, so it's not outdated wiring). The hum would even kick in just by touching the ground prong on the power cord to the electrical socket. The degree of the hum also seemed to vary when wiggling the power cord at the electric socket. We also tried several different XLR cables and two different inputs into the PA.

 

The sound engineer is absolutely convinced that it's something wrong with the amp. I'm not really sure what to think. I do remember that I had this same problem with a Tech 21 Trademark 30, except that the hum started immediately. Strangely enough, I do recall running a Tech 21 Power Engine 60 into the PA via the XLR out once without any problems.

 

So to summarize: Massive hum when connected to PA regardless of whether amp is on or not; regardless of cable or electric circuit the amp is plugged into; regardless of what is plugged into the amp (guitar, pedal board, or nothing). The hum only became apparent about two hours into it being connected.

 

Do you guys have any clue what is going on or how I can fix it? I really like this amp and want to keep using it. The hum only happens when it's connected to the PA; otherwise, there isn't any hum. And it's not a subtle, light hum, but a massive, grinding, buzzing hum.

[agedhorse]

This is possibly due to a damaged XLR line driver, though I would expect the noise only when powered up. The fact that it happens only when the ground pin of the power plug is connected to the power ground indicates that possible the neutral and ground are reversed (or tied together at another place in addition to the mandatory service entrence) and it bacame noise when another set of loads on the same circuit, shared neutral or neutral feeder were energized (lighting perhaps?) causing the ground to reference the noisy neutral so there would be not just a nominal ground loop but a more substantial current flowing. Neutral and ground are only at the same potential at the service entrence only and will vary depending on the voltage drop on the neutral.

 

The reason why the ground lift did not solve this problem is that ground lifting is done in several ways, and what may have been inserted is a decoupling network which works the dame as a ground loop but has other components (like back to back diodes) the will conduct once the set voltage threshold is passed.

 

Do NOT do as our friend "WHERE" on this forum enthusiasticlly recommeds and lift the power ground as this places you in a potentially dangerous or lethal position.

 

The first thing the club should do is to check the items I suggest above... I'll bet 10:1 odds that it's either a missing power ground, a nuetral tied to power ground at an incorrect location, or neutral and ground reversed somewhere causing circulating currents to flow on the ground and contaminate the reference.

 

Let us know what you find.

 

Another possible bandaid (but safe for you) fix is to insert a 1:1 audio isolation transformer from your direct out to the PA connection with the pin 1 lifted. This will isolate all possible problems except for a damaged XLR line driver. Another remote possibility is for phantom power to be present on the console channel, and either the DI out or something in the club's mic cabling to be shorted either pin 2 to 1 or 3 to 1 causing an unbalanced phantom power condition and any ripple present on the phantom power source would then be amplified by the mic preamp's gain factor since there will be no common mode rejection.

 

Didn't know there were so many possibilities to such a simple sounding problem eh?

[AtomHeartMother]

Originally posted by agedhorse This is possibly due to a damaged XLR line driver, though I would expect the noise only when powered up. The fact that it happens only when the ground pin of the power plug is connected to the power ground indicates that possible the neutral and ground are reversed (or tied together at another place in addition to the mandatory service entrence) and it bacame noise when another set of loads on the same circuit, shared neutral or neutral feeder were energized (lighting perhaps?) causing the ground to reference the noisy neutral so there would be not just a nominal ground loop but a more substantial current flowing. Neutral and ground are only at the same potential at the service entrence only and will vary depending on the voltage drop on the neutral. The reason why the ground lift did not solve this problem is that ground lifting is done in several ways, and what may have been inserted is a decoupling network which works the dame as a ground loop but has other components (like back to back diodes) the will conduct once the set voltage threshold is passed. Do NOT do as our friend "WHERE" on this forum enthusiasticlly recommeds and lift the power ground as this places you in a potentially dangerous or lethal position. The first thing the club should do is to check the items I suggest above... I'll bet 10:1 odds that it's either a missing power ground, a nuetral tied to power ground at an incorrect location, or neutral and ground reversed somewhere causing circulating currents to flow on the ground and contaminate the reference. Let us know what you find. Another possible bandaid (but safe for you) fix is to insert a 1:1 audio isolation transformer from your direct out to the PA connection with the pin 1 lifted. This will isolate all possible problems except for a damaged XLR line driver. Another remote possibility is for phantom power to be present on the console channel, and either the DI out or something in the club's mic cabling to be shorted either pin 2 to 1 or 3 to 1 causing an unbalanced phantom power condition and any ripple present on the phantom power source would then be amplified by the mic preamp's gain factor since there will be no common mode rejection. Didn't know there were so many possibilities to such a simple sounding problem eh?

 

 

Honestly, I don't understand a thing you just wrote. That all went way above my head. I'm not even sure what to say to them. Thanks though. Maybe I just need to re-read it a few times and maybe print your response off and show it to the sound people.

 

Anyway, here is a quick update:

 

 

I went back and tried to diagnose the hum/buzz again. Only guitar into amp, then XLR Sansamp out to the PA. The only thing connected to the mixer was the TM60. I still got the hum/buzz. The ground lift on the back did little to nothing. However, there was one outlet, a really, really old one, that didn't give me the hum/buzz on a consistant basis. If I wiggled the plug at the outlet, the hum would come in and out. Sometimes if I shook it enough or something the hum would stay. If I shook it some more, it'd go away.

 

The person I went with informed me that he thought that for whatever reason, this outlet (on a circuit of its own...a really old one) was NOT grounded. It was a 3 prong type though.

 

So, I guess I'm still unsure as to what's going on. I can just plug into that one and hope for the best, I suppose. The person I was with said that it's some ground loop between the mixer and the amp. How would I fix this? The ground lift button does little to nothing.

 

As a side note, the headphones out into a direct box then into the XLR in of the mixer does not produce the hum sound with the direct box ground switch on (or off, I can't remember).

 

 

 

 

Also, I don't know if this helps at all, but...

 

I plugged the XLR out of the TM60 into my little digital recorder that I had with me (Zoom MRS8) and I didn't get any hum when monitoring through headphones. I had the amp and MRS8 plugged into circuits that gave me hum before. So it must be something with the combination of my amp and the PA.

 

Still, the thing that is just baffling me is that I didn't get any hum or any problems at all until 2 hours into having it all setup and playing.

[agedhorse]

Show what I wrote to your friend, maybe it will help with the understanding.

 

You always want to be sure you have a correct safety ground.

 

My vote is that the neutral and ground are either reversed or tied together at an intermediate location and not bonded at the MAIN service panel.

 

The ground lift may not work in this situation for the reason I indicated.

[AtomHeartMother]

 

Originally posted by agedhorse Show what I wrote to your friend, maybe it will help with the understanding. You always want to be sure you have a correct safety ground. My vote is that the neutral and ground are either reversed or tied together at an intermediate location and not bonded at the MAIN service panel. The ground lift may not work in this situation for the reason I indicated.

 

 

OK. I'll have them check that out next time I'm there.

 

One question: If something is wrong with the electrical wiring or the wiring of the PA, why is only my amp that is showing problems? How come the singers mics, the clavinova, the acoustic guitarist, etc. don't have any problems?

 

 

Another question:

 

If I can't get this figured out, I may have to look into just mic'ing the amp, which the sound people aren't too fond of and also something that I haven't really done before. I have my amp on a chair about three feet in front of me with the amp tilted at like a 30-40 degree angle. So it'll be hard to place a mic on a stand in front of it or something. How would it sound to just drape a mic over the top of the amp and just hang it in front of the speaker? Like crap? I know that mic placement is a real art.

 

Also, how are SM58's for mic'ing amps? That's all they seem to have.

 

[agedhorse]

Your amp may show up then problem due to the internal grounding path that was chosen in the design. Your amp may be quieter than others in the event of a different scenario though.

 

Micing the amp is another option. I would want to be sure the power is indeed correct before plugging anything into a questionable source though.

[where02190]

You mentioned The degree of the hum also seemed to vary when wiggling the power cord. It's possible the ground connection on the AC plug is lose.

 

Have you tried putting a 1:1 transformer inline with the XLR? Does the Sansamp have 1/4" outs? Try running through them and a DI.

 

 

 

Originally posted by agedhorse Do NOT do as our friend "WHERE" on this forum enthusiasticlly recommeds and lift the power ground as this places you in a potentially dangerous or lethal position.

 

 

First off asshole, your not my friend, and I'm certainly not yours.

 

Second, I NEVER recommended this solution for this problem, but thanks for showing your ignorace in the scenario that I did recommend it for , WHEN THERE ARE MULTIPLE AMPS. (Yo clueless, multple means more than one, which is NOT the case here.) You obviously made your usual I am the god of the forum and you are scum remarks on that post as well without even bothering to read or comprehend what I wrote, and this simply proves it.

 

Once again you show your true colors.

[6Imzadi]

 

Originally posted by where02190 You mentioned The degree of the hum also seemed to vary when wiggling the power cord. It's possible the ground connection on the AC plug is lose.

 

 

Replace the power cord to the amp.

[AtomHeartMother]

 

Originally posted by where02190 You mentioned The degree of the hum also seemed to vary when wiggling the power cord. It's possible the ground connection on the AC plug is lose. Have you tried putting a 1:1 transformer inline with the XLR? Does the Sansamp have 1/4" outs? Try running through them and a DI. First off asshole, your not my friend, and I'm certainly not yours. Second, I NEVER recommended this solution for this problem, but thanks for showing your ignorace in the scenario that I did recommend it for , WHEN THERE ARE MULTIPLE AMPS . (Yo clueless, multple means more than one, which is NOT the case here.) You obviously made your usual I am the god of the forum and you are scum remarks on that post as well without even bothering to read or comprehend what I wrote, and this simply proves it. Once again you show your true colors.

 

 

 

If the ground connection on the AC plug is loose, wouldn't I get hum all the time, regardless if I was plugged into the PA or not (i.e. just plugged into the wall and playing)?

 

I guess I'm not sure what a 1:1 transformer is.

 

Unfortunately, the Sansamp portion does not have a 1/4" out. The headphone out is 1/4" and I did run it through a DI box and with success (and no hum) when turning on some ground switch on the DI box. Unfortunately, the headphone out disconnects the internal speaker and I use the amp to monitor myself on stage.

 

However, I am going to try running an XLR-1/4" TRS (balanced) cable from the TM60 into a DI and then into the PA. I'm hoping that this will take care of the hum as it did when running from the 1/4" headphones out. I don't know if this will change anything though.

[tlbonehead]

Originally posted by AtomHeartMother If the ground connection on the AC plug is loose, wouldn't I get hum all the time, regardless if I was plugged into the PA or not (i.e. just plugged into the wall and playing)?

An ungrounded amp on its own shouldn't have hum just from not being grounded. If that's what you were asking.

[AtomHeartMother]

 

Originally posted by tlbonehead An ungrounded amp on its own shouldn't have hum just from not being grounded. If that's what you were asking.

 

 

All right. Well, I'm going to be taking the amp into a tech tomorrow at the request of the sound guy. I don't think it's necessarily something wrong with the amp, but I'll do it to ease his mind. I'll have the tech check out the cable and internal AC stuff.

 

Although, I'm probably just wasting my money as I don't see how he could possibly diagnose anything without the PA.

[where02190]

 

Originally posted by AtomHeartMother If the ground connection on the AC plug is loose, wouldn't I get hum all the time, regardless if I was plugged into the PA or not (i.e. just plugged into the wall and playing)?

 

 

Not necessarily, especially if the connection is intermittant.

 

 

Originally posted by AtomHeartMother I guess I'm not sure what a 1:1 transformer is.

 

 

http://www.amazon.com/exec/obidos/ASIN/B0006N3ITQ/nextag-mi-20/ref=nosim

[Craig Vecchione]

 

Originally posted by where02190 You mentioned The degree of the hum also seemed to vary when wiggling the power cord. It's possible the ground connection on the AC plug is lose. Have you tried putting a 1:1 transformer inline with the XLR? Does the Sansamp have 1/4" outs? Try running through them and a DI. First off asshole, your not my friend, and I'm certainly not yours. Second, I NEVER recommended this solution for this problem, but thanks for showing your ignorace in the scenario that I did recommend it for , WHEN THERE ARE MULTIPLE AMPS . (Yo clueless, multple means more than one, which is NOT the case here.) You obviously made your usual I am the god of the forum and you are scum remarks on that post as well without even bothering to read or comprehend what I wrote, and this simply proves it. Once again you show your true colors.

 

 

 

To address your claim that this thread doesn't have the same "scenario"; the number of AC devices (amps etc.) doesn't matter at all. The signal chain doesn't matter. What does matter is the FACT that if an outlet is a three-prong grounded, then it is a code violation to use a ground lift device. PERIOD.

[where02190]

Still haven't seen chapter and verse on that, have we?

 

Funny how many professional guitarists do it all the time and don't get arrested for breaking the law.

 

The little clique with the big roar sounds off. Man I really almost feel sorry for you guys, wannabees in training. Almost, but not quite. Here's a dollar, go buy a clue.

 

People, don't be intimidated by these jerks. Sadly, unlike many other very helpful forums, this one seems to have a little club of "we're right everyone else sucks" small fish in the big pond. Perhaps they are intimdated, or feel threatened or just have an superiority complex, but whenever anyone suggests something other than their methods, they talk {censored}. Just ignore it, and take all the advise here as you wish, then make your own decisions.

[Craig Vecchione]

 

Originally posted by where02190 Still haven't seen chapter and verse on that, have we? Funny how many professional guitarists do it all the time and don't get arrested for breaking the law. The little clique with the big roar sounds off. Man I really almost feel sorry for you guys, wannabees in training. Almost, but not quite. Here's a dollar, go buy a clue. People, don't be intimidated by these jerks. Sadly, unlike many other very helpful forums, this one seems to have a little club of "we're right everyone else sucks" small fish in the big pond. Perhaps they are intimdated, or feel threatened or just have an superiority complex, but whenever anyone suggests something other than their methods, they talk {censored}. Just ignore it, and take all the advise here as you wish, then make your own decisions.

 

 

Which is it, "Just ignore it', or "take all the advice here as you wish"? You can't even avoid contradicting yourself in the same sentence.

 

So are you going to argue the points I made? If so, please do provide "chapter and verse" stating it's okay to defeat AC grounding whenever it suits your needs. After all, you're the only one here stating it's okay. Otherwise quit your whining and just once admit you're wrong.

[Craig Vecchione]

Originally posted by where02190 People, don't be intimidated by these jerks. Sadly, unlike many other very helpful forums, this one seems to have a little club of "we're right everyone else sucks" small fish in the big pond. Perhaps they are intimdated, or feel threatened or just have an superiority complex, but whenever anyone suggests something other than their methods, they talk shit. Just ignore it, and take all the advise here as you wish, then make your own decisions.

 

I want to address this separately from the rest of your "response". Show me where I've written ANYTHING that resembles "talking shit" or a "we're right everyone else sucks" attitude. And your way of proving your point is to call me a jerk?

 

You, quite to the contrary, called Andy an asshole as well as your usual insults. All for pointing out an unsafe situation. The guy's an EE and has special knowledge of power systems. I'm quite confident I know more about the electrical code than you. If you can't argue a point without resorting to name-calling, just stay home pal.

 

And for Pete's sake, at least get your saying's right. It's "big fish in a small pond".

[agedhorse]

NFPA 70B:

 

16-2.6 The green equipment grounding conductor of the cordset must be attached to the groundingterminal of the device.

 

16-4 Adapters... adapters should not be used to bypass the equipment ground...

 

17-4.2 All power equipment, unless double insulated and so marked, are required to be grounded through an additional grounding conductor in the cord and the grounding prong of the attachment plug. The integrity of this grounding circuit is necessary for the protection of life... Experience has shown that the grounding prongs are frequently removed... and this practice shall not be permitted.

 

17-4.4 To avoid accidents, the green conductor must ALWAYS and ONLY be used to connect the frame of the tool or equipment to the grounding prong of the attachment plug...

 

The ANSI/NFPA 70B publication is generally the most common publication a site inspector will cite for any inspection of equipment or practices of equipment that is on the load side of a power recepticle.

 

Nowhere does this manual state that because Nick says it's permissable to lift the safety ground from the attachment plug to a power system, and Nick, it in fact says it is NOT ok to do so.

[where02190]

Nothing there in the way of legal requirements.

 

I got the saying right in the context of how I intended, you being the small fish, this being the big pond.

[6Imzadi]

 

Originally posted by agedhorse NFPA 70B: 16-2.6 The green equipment grounding conductor of the cordset must be attached to the groundingterminal of the device. 16-4 Adapters... adapters should not be used to bypass the equipment ground... 17-4.2 All power equipment, unless double insulated and so marked, are required to be grounded through an additional grounding conductor in the cord and the grounding prong of the attachment plug. The integrity of this grounding circuit is necessary for the protection of life... Experience has shown that the grounding prongs are frequently removed... and this practice shall not be permitted. 17-4.4 To avoid accidents, the green conductor must ALWAYS and ONLY be used to connect the frame of the tool or equipment to the grounding prong of the attachment plug... The ANSI/NFPA 70B publication is generally the most common publication a site inspector will cite for any inspection of equipment or practices of equipment that is on the load side of a power recepticle. Nowhere does this manual state that because Nick says it's permissable to lift the safety ground from the attachment plug to a power system, and Nick, it in fact says it is NOT ok to do so.

 

 

ANYWHERE in the code the word shall is used consitiutes mandatory compliance. It is the law, and enforcable by fine and/ or imprisonment.

[tlbonehead]

Where must have gotten a new book to read for Christmas.

[agedhorse]

Originally posted by where02190 Nothing there in the way of legal requirements.

I'd love to see how a pro like you would tell the inspector this. HE is the authority having jurisdiction and what he says goes. Some day you will say the wrong thing to the wrong guy and understand. It's not if but when you gat caught.

[Craig Vecchione]

 

Originally posted by where02190 Nothing there in the way of legal requirements. I got the saying right in the context of how I intended, you being the small fish, this being the big pond.

 

 

 

Regarding the former; The NEC is indeed merely a document. That document, or a version modified to include more specific wording as required, when adopted by an authority having jurisdiction, such as your local city, township, village or county, becomes law. As law, it is indeed a "legal requirement". That's how building codes, plumbing codes, electrical codes, etc. are implemented. Surely someone as smart as you imagine yourself would know this.

 

Do yourself the favor of calling your local building department and speak with the inspector to verify what I've just said. Do us the favor of ceasing to be so obnoxious in your ignorance.

 

Regarding the latter, you're a regular Norm Crosby. Your intented misuse has no meaning....of course I'm a small fish in a big pond. Good grief.

[AtomHeartMother]

Update:

 

I went back to the place to test things out and whatnot, but the sound guy wasn't there. So I just did a few things that an expert amp/electronics tech at a local, well-known guitar shop told me. The first was the use one of those 3 prong to 2 prong adapters. Sure enough, it removed all of the hum and buzz (I had both hum and buzz). I was kind of concerned about lifting a ground like this, but he assured me that it is safe, and I trust this guy. He's a well-respected expert in electronics who is often consulted by recording studios, live venues, and other places in regards to problems caused by electrical issues. So I suppose that he knows his stuff. He said not to worry about the ground lift plug thing as the amp is grounded through the PA or something. He said just to make sure to have the ground lift on the amp (the little button) off and to test this by touching a string end on one of the tuning posts to a mic to check sparks and whatnot.

 

The other thing he eluded to was to use a XLR to 1/4" cable into a direct box and then into the PA, in case that the XLR Sansamp out on the TM60 is indeed NOT truly balanced, which is supposedly often the case with XLR out on amps. Well, with the ground lift button on the DI box on (or maybe it was off, I can't remember), the noise did go away. This was without the little ground lift plug adapter thing from the previous procedure.

 

 

So I suppose I have two options. Is one prefereble as far as the signal go? Would running through a DI box and with the extra cables cause any change in the signal? Will one of the two methods work better than the other? They both seem to eliminate the noise.

[6Imzadi]

OMG, here we go again......

[preacherman672]

 

Update: The first was the use one of those 3 prong to 2 prong adapters. Sure enough, it removed all of the hum and buzz (I had both hum and buzz). I was kind of concerned about lifting a ground like this, but he assured me that it is safe, and I trust this guy. He's a well-respected expert in electronics who is often consulted by recording studios, live venues, and other places in regards to problems caused by electrical issues. So I suppose that he knows his stuff. He said not to worry about the ground lift plug thing as the amp is grounded through the PA or something. He said just to make sure to have the ground lift on the amp (the little button) off and to test this by touching a string end on one of the tuning posts to a mic to check sparks and whatnot.

 

 

Have a nice death.