Grounding. Check that the mains outlet your amp is plugged into is properly earthed.

Is this a venue you've played before in a more normal setup, with this same guitar and amp, without this noise issue?
How long are the cables between your guitar, (pedal board), and long run to the amp?
Are you 100% sure they all, (especially the long one) are well shielded instrument cables, and none of them are speaker cables?
Do any of those cables run anywhere near cables powering the lights?
Did you notice any change in severity of the hum relative to the direction you were facing?
Single coil pickups or humbuckers?
If it's a guitar with single coil pickups, was it equally bad in the 2&4 positions of the pickup selector?

Jeremy...

Stage lights are often on rheostats/dimmer switches; and these can also cause noise in audio equipment.

In addition to what Bos and Hawk have mentioned, you may want to look into a power conditioner of some kind; Furman makes many different models, from basic surge/spike protectors, to actual conditioners that are meant to filter out RFI and EMF, and which can keep your voltage consistent and clean. Some models will even provide additional amperage of reserve current so that your gear is always receiving optimal power.

Of course, the more you want the conditioner to do, the pricier it will be... ;)

http://www.sweetwater.com/c960--Furman--Power_Conditioners

you can also email them at:
info@furmansound.com

When I have had hum or static caused by a relatively long run between guitar and amp, I have had fairly good results by using two passive DI boxes to convert the bulk of the run to balanced lines via XLR mic cables. One box close to the guitar converts to XLR, another close to the amp converts back to unbalanced 1/4". Might be worth a try!
~Jeff

Perhaps a Radial SGX would help.

http://www.musiciansfriend.com/pro-audio/radial-engineering-sgi-tx-rx-studio-guitar-interface

I guess it would be relevant to know the make/model of the guitar amp, or more importantly its age, since some of the old ones had no electrical ground at all. A power conditioner will be of limited usefulness if the amp plugged into it is ungrounded.

I'm also concerned there may be a pedalboard plugged into one circuit and the amp into another circuit.

I never trust an instrument cable of more than 20ft. The loss is significant, and the guitar (strings, pickups, cables) make an awfully nice antenna.

The Radial Eng. system is the best way to do a long run and have an impedance optimized for the inputs of a guitar amp.

Would an isolation transformer be helpful in this situation?

Something like this?

https://www.tripplite.com/isolator-series-120v-250w-isolation-transformer-based-power-conditioner-2-outlets~IS250/

It's runs about $100 on Amazon, for the 250w version.

Thanks for the replies everyone! Sorry for being late to the show here, been super busy.

dvdhawk, post: 442736, member: 36047 wrote: How long are the cables between your guitar, (pedal board), and long run to the amp?
Are you 100% sure they all, (especially the long one) are well shielded instrument cables, and none of them are speaker cables?
Do any of those cables run anywhere near cables powering the lights?
Did you notice any change in severity of the hum relative to the direction you were facing?
Single coil pickups or humbuckers?
If it's a guitar with single coil pickups, was it equally bad in the 2&4 positions of the pickup selector?

The cable from my guitar to the pedal board is less than 10 ft. Possibly 5? I use a very short patch cable from the board to some kind of DI they have that runs backstage to my amp. I have no idea how long the cable is. I expect pretty lengthy cause the back room is pretty far from where I am on stage.
I don't believe the cables are near the ones running the lights. All the lights are mounted high above the stage and I haven't noticed any wires running down near the stage.
The severity of the hum changed a tad bit when turning different directions. But it would mostly just fade and wobble for a second or so and be right back to it's normal annoying self.
I have one humbucker and 2 single coil pickups. They're Seymour Duncans.
I don't remember well if the noise varied between the different pickup positions. I believe they might have been but not positive on that one.

thatjeffguy, post: 442743, member: 38103 wrote: When I have had hum or static caused by a relatively long run between guitar and amp, I have had fairly good results by using two passive DI boxes to convert the bulk of the run to balanced lines via XLR mic cables. One box close to the guitar converts to XLR, another close to the amp converts back to unbalanced 1/4". Might be worth a try!

Thanks Jeff! I may look into that.

dvdhawk, post: 442747, member: 36047 wrote: I guess it would be relevant to know the make/model of the guitar amp, or more importantly its age, since some of the old ones had no electrical ground at all. A power conditioner will be of limited usefulness if the amp plugged into it is ungrounded.

I'm also concerned there may be a pedalboard plugged into one circuit and the amp into another circuit.

I never trust an instrument cable of more than 20ft. The loss is significant, and the guitar (strings, pickups, cables) make an awfully nice antenna.

I have a Vox VR30R. It has a tube in it and I believe it was made in the last 10 years or less. I have no idea if the pedal board and amp are being powered by different circuits, but I believe it's very possible. The venue I'm playing at is fairly large.

DonnyThompson, post: 442738, member: 46114 wrote: In addition to what Bos and Hawk have mentioned, you may want to look into a power conditioner of some kind; Furman makes many different models, from basic surge/spike protectors, to actual conditioners that are meant to filter out RFI and EMF, and which can keep your voltage consistent and clean. Some models will even provide additional amperage of reserve current so that your gear is always receiving optimal power.

Some of the stage hands suggested that a power conditioner might help but before buying one I'd like to pin down the source of the problem so I don't buy it and it does nothing for me.

Power conditioners are always a good investment, in my opinion. Every single rack I own has at least one Furman, ETA, or Tripp-Lite power conditioner in it. My guitar rig gets its power from the one that powers the monitor amps.

If you're just running a garden-variety DI, I'd be curious to hear how you get back from the XLR to ¼" at the amp input at the far end of the cable.

Also, check the DI's Ground Lift switch if it has one. Some DI's are marked in a way that can be confusing, so remember that when you're engaging the button, you're breaking the path the shield has to ground. In a lenghty XLR run, with who knows what kind of conversion back to ¼", you probably want all the benefit of sending the shield to ground you can get (all other things be correct). If there's a second DI at the amplifier end, experiment with that Ground Lift switch too.

If the humbucker is quiet and the single-coils are quiet, that's a clue too (that might lead us in a different direction).

A modern amp like that would have been grounded when new, so as long as you haven't deliberately removed the ground prong, it should have one. It's not like some vintage 60's Fenders that I've had with 2-prong (non-polarized) power cords.

The problem with power conditioners is they don't do much if anything to filter noise, particularly ground hums.

The isolation transformer has a transformer which breaks the physical ground connection and has its own isolated grounding point for the plugs. The casing has/is a faraday cage to reject rfi so it's design addresses both common noise issues

How well it works in each case I can't gaurrentee, but they're designed on paper to handle those things.

I'm not suggesting power conditioners should be used or aren't consvienent, I've just never heard them make an audible difference in noise.

Ground lift switch on the back of a dj's mixer near his power plug did remove nuisance noise thru the system that was otherwise a nightmare. When you lift the ground on power (not audio as far as a iknownat least) you leave your equipment vulnerable in certain situations. You could try one of those little orange 3 prong to 2 prong adapters to lift the ground.

The advantage to the isolation transformer is it leaves your equipment protected.

kmetal: One has to be extremely careful using the "3 to 2 prong" adaptors that effectively lift ground if the tab isn't grounded via the outlet box to an effective ground, especially in an older building!

In the old "knob and tube" days, there were only two conductors on insulators running behind the wall to outlets, switches, or fixtures. Sometimes, the wires running behind the wall were the same color (typically cloth black wire) which was inviting a polarity reversal. In the event the connections to the outlet were reversed, the "hot" AC effectively was applied to the chassis of certain items such as AC/DC radios, AC/DC television receivers, etc. There were documented instances of people electrocuted from "hot chassis" items.

Another situation arises in certain venues where incoming AC power is supplied in three phase delta. Transformers (across a "leg" of the delta) are typically provided for 117 volt single phase circuits since the "delta" doesn't really have earth ground. In the event 117 v single phase power was directly derived from a delta connection without a transformer, both "sides" of the AC could be elevated. Besides the hazard, the lack of true earth ground will show up as undesirable noise on audio circuits. (The typical 208 volt three phase "wye" connection has a grounded neutral so single phase power can be derived from one phase to ground; always check the voltage and polarity.)

The isolation transformer will provide isolation from the mains as well as permit connection of a earthed ground. If you are unfamiliar with the venue or suspect you are dealing with "dirty electricity", get out the DMM or one of those pocket AC outlet polarity checkers; check the voltage, look for polarity reversal, and prepare to use a isolation transformer. Consult a qualified electrician if necessary. BE CAREFUL!

Around "dirty" electricity, it's likely the isolation transformer primary will connect to the incoming or wall AC supply, the ground reference may be derived from a source such as a grounded metal water pipe, and the secondary powers the audio equipment. The "Hum-X" line filters also help with line noise.

dvdhawk, post: 442747, member: 36047 wrote: I guess it would be relevant to know the make/model of the guitar amp, or more importantly its age, since some of the old ones had no electrical ground at all. A power conditioner will be of limited usefulness if the amp plugged into it is ungrounded.

I'm also concerned there may be a pedalboard plugged into one circuit and the amp into another circuit.

I never trust an instrument cable of more than 20ft. The loss is significant, and the guitar (strings, pickups, cables) make an awfully nice antenna.

dvdhawk: Good points. Two prong non polarized plugs can be trouble; amp plugged in outlet one way, pedalboard plugged in the other way may lead to noise. 9 ft cables are 1/4 wavelength at CB radio frequencies. Unbalanced shielded Hi-Z guitar has capacitance of 10 to 20 pf/ft. 20 feet of unbalanced Hi-Z guitar cable with 20 pf/ft capacitance represents "shunting" the input of the amplifier with 400 pF of capacitance...if the amplifier input impedance is on the order of 200 k ohms unbalanced, there is a time constant of 12.5 kHz involved. Nearby AM broadcast station - if you hear the radio station through the equipment, audio rectification of the AM carrier is occurring. Jeffguy had a good idea using two passive D/I boxes to make the long cable run low impedance to the amp. (Should work as long as long as no strong RF or other transients are present.)

My late 60's Fender has a 2-prong, non-polarized plug (which means the 2 blades are the same size, and you can plug it into the receptacle either way), and on the back of the amp is a "polarity" switch. Putting a grounded cable on it is one of the few modifications you can make to a vintage Fender that hardcore collectors will give you a pass on - as long as it's a genuine red plug Fender cable. They don't seem to mind, because it really is dangerous the way they made them back then.

Back in the 70's when I first started playing, some of my friends who were slow-learners, wouldn't think about checking their polarity until AFTER they stepped up to their mic and got shocked in the mouth. I got bit once and learned to check it by grabbing the neck of the guitar with one hand (making sure I had good contact with the strings), and quickly brushing the back of the other hand across the windscreen of the mic. If it was backwards you got a quick,mild tingle of a shock, but it was a whole lot better than getting shocked in the mouth by what felt like the full 110v.

If they want UL to sign off on them, all modern (US) devices have to have a ground to ensure there can only be one orientation of the hot and neutral, assuming the receptacle is wired correctly (which is also a dangerous assumption). If it's a device that can safely operate ungrounded, one blade is wider than the other so you can't get the hot and neutral reversed. If it has neither of those, then it's something they've deemed poses no potential shock hazard regardless of electrical polarity and absence of earth ground.

A power conditioner can absolutely filter out noise, if everything else is kosher - Unless of course you plug your power conditioner into the wall using a 3-prong to 2-prong adapter, at which point all bets are off.

I've been shocked by an old fender amp myself at the studio.

dvdhawk, post: 443415, member: 36047 wrote: A power conditioner can absolutely filter out noise,

Please don't take this as argumentive, it's a genuine question. What kind of noises? I've never had one take out any sort of electrical noises like bad grounding, leaking mains transformer, or things like mechanical compressors. I've tried regular furmans and 1200$ monster voltage regulators, and ground lifts on passive dis (in the case of the leaky mains transformer and just genernally gross power) the two prong thing didn't work in that case either. In that rooms case you had to rotate 360 and point in a certain direction that was the quietest until they changed the leaky transformer out on the roof years later.

So I curious in what instances they do clean up power audibly?

Also to reiterate I did say the ground lift leaves equipment vurnerable. I lack a certain expertise but I did leave that warning. Also in the case of the dj I told him I wouldn't do it if it was my mixer.. fwiw the 2 prong thing is mostly useful as a diagnostic tool rather than a fix, asssuming you make it thru it alive.

The reason I'm wanting to clear up the power conditioner isn't to be a jerk, rather I think there is a lot of misunderstanding as to what they do. I've got plenty of room to learn, but I think the public in general can be mis lead by the ads on those things.

I've also seen purple lighting shoot out of a Mesa triple rectifier and up the wall. Nobody got shocked, my buddy shredding didn't even notice. It looked like one of those little globes at the mall where you touch it and lightning goes where your finger is. It's one of the gnarliest things I've seen...

Don't worry, I didn't take it as argumentative at all Kyle. I think we're both trying to dispel myths.

I've heard audible improvements in countless situations: guitar rigs, bass rigs, installed PA, portable PA, recording equipment, studio monitors, video equipment. I don't know what else I can tell you. I've seen a couple real problem cases where they barely made a dent, but for the other 99% of the time they will usually do exactly what they're intended to do, if you've got everything else squared away (all the way back to the breaker panel).

Just a few examples:

The guy I team up with on certain projects, has Focusrite Green series, Avalon 747, Vintage Lexicon and the like. Every piece of audio gear he owns has to be plugged into his Tripp-Lite Isobar, otherwise you will hear a distinct 'snap' through his Events and KRKs every time his fridge or furnace kicks on. Anything with motors (furnace fan, fridge compressor), ballasts, voltage-dimming triacs, etc. has a lot of potential to pollute power of everything it shares a bus with in the breaker panel. Electricians want to keep the load balanced between the legs, but Rod G. recommends keeping your studio gear on one leg, and lighting and HVAC separate for that reason.

There may be some correlation between the quality of the gear and its ability deal with (or maybe be clean enough to notice) noisy power. I remember a thread on another site where the project studio owner was upgrading to a new (at that time) Toft ATB console. He loved the console, but had a noise problem with the Toft he did not have with the previous (Mackie, I believe) mixer in the exact same set-up / environment. After much complaining to customer support they recommended he try a Furman conditioner and putting the Furman inline was all it took - noise vanishes completely.

The bass player I work with most often has top-notch gear: Modulus bass, nice SWR head, Markbass cabinets, TL Audio Tube Compressor, and Furman conditioner. He bought the Furman about 10 years ago when we played regularly at a place that had neon lights, dimmed house-lights, and a full kitchen. The place had an in-house PA, so I wouldn't have had any racks or conditioners with me, and we all had noise problems that first night. Second night in, I brought a conditioner and let the other guys plug into it too. Pre-Furman, constant buzz, especially the bass amp for some reason. Post-Furman (with absolutely no other changes to the bass rig), perfectly quiet. It was an immediate 100% improvement. The power was dirty, plus neon nearby is always a big problem with single-coil guitar pick-ups. Stratocasters are fantastic antennas. The first night I noticed if I pointed the headstock South (let's say), the noise was horrendous. The more I turned toward the west, the better it got. North was not great, but not as bad as South, and so on. I got through the first night by mostly using the 2 & 4 (out of phase) positions on the Strat's 5-way switch and playing kinda sideways to the audience if I needed the bridge pickup. That second night, clean power, (and a tele with noise-cancelling pick-ups) and everything was perfect. Later I brought in the Strat again to compare, and it was still getting minor neon interference, but maybe 5% of what it was on night #1.

You usually don't need a super expensive brand/model to do the trick. I think ETA is as good as any, and quite a bit less expensive than most.

And for the record, I have a few 3-prong to 2-prong adapters that I will use to help identify a problem, but never as a long-term solution. They have their place.

Interesting. I certainly don't doubt your experience. I'm guessing the instances I've dealt with have either been too severe for a power conditioner or something they're not meant to help. I'm glad to know that they are in fact helpful in some cases.

So the next thing I wonder is do ISO transformers and power conditioners attack similar problems. Is one prefered over the other for certain things? Are they different in design.?

I don't mean to de rail the thread but I do think it's relevant conversation about hums and buzzes.

Power conditioners use a variety of electronic components to filter out noise present in the electrical line. They're designed to get you the purest 60Hz sine wave possible from your AC line.

Isolation transformers are extremely useful too, but they work in a different way. When you're powered through an iso transformer, you're no longer physically connected to the power source. It's all magnetic field, so it makes a great buffer between you and dirty power that runs the rest of the building. A tube guitar amp is probably going to want a good bit more than a 250w iso transformer. On paper, if the amplifier has a 2-ampere fuse, that's 240w of max. power consumption @120v. 10w is not much headroom. A Mesa Triple Rectifier uses a 4A slow-blow fuse, making that 480w of max. consumption and since it's designated as slow-blow they're telling you to expect spikes beyond 4A (480w). I'm looking at a Mesa manual right now, and love the switch below the fuse that lets you select what kind of power you want "Bold" or "Spongy".

A balanced power transformer rejects AC noise much like and balanced audio circuit does, achieving the same 120v output potential using equal and opposite 60v legs and letting the noise cancel itself out. Very clever.

A really good Uninterrupted Power Supply can also be capable of a pure-sine output.

Awsome! Great clarification. lol I had a lot of fun w those Mesa amps.

So in an ideal world would you want to have all three items conditioner, ISO transformer, and battery backup? Is that unecesary resundence?

I'm assuming a case where 'typical' power is supplied from the breaker, i.e. Nothing special as far as circuits go.

dvdhawk, post: 443415, member: 36047 wrote: My late 60's Fender has a 2-prong, non-polarized plug (which means the 2 blades are the same size, and you can plug it into the receptacle either way), and on the back of the amp is a "polarity" switch. Putting a grounded cable on it is one of the few modifications you can make to a vintage Fender that hardcore collectors will give you a pass on - as long as it's a genuine red plug Fender cable. They don't seem to mind, because it really is dangerous the way they made them back then.

Back in the 70's when I first started playing, some of my friends who were slow-learners, wouldn't think about checking their polarity until AFTER they stepped up to their mic and got shocked in the mouth. I got bit once and learned to check it by grabbing the neck of the guitar with one hand (making sure I had good contact with the strings), and quickly brushing the back of the other hand across the windscreen of the mic. If it was backwards you got a quick,mild tingle of a shock, but it was a whole lot better than getting shocked in the mouth by what felt like the full 110v.

If they want UL to sign off on them, all modern (US) devices have to have a ground to ensure there can only be one orientation of the hot and neutral, assuming the receptacle is wired correctly (which is also a dangerous assumption). If it's a device that can safely operate ungrounded, one blade is wider than the other so you can't get the hot and neutral reversed. If it has neither of those, then it's something they've deemed poses no potential shock hazard regardless of electrical polarity and absence of earth ground.

A power conditioner can absolutely filter out noise, if everything else is kosher - Unless of course you plug your power conditioner into the wall using a 3-prong to 2-prong adapter, at which point all bets are off.

dvdhawk: Is your late '60's Fender amp with the two prong non-polarized plug a tube type unit with a power transformer? If the amplifier uses 6 volt tubes such as EL34, 6L6, etc., a power transformer is probably used to obtain heater and B plus voltages for the tubes. I wrote a comment a while back in response to someone getting shocked off a LA-2 unit.

Some equipment manufacturers connected low value capacitors (typically 0.001 to 0.01 uF, 600 volt paper or mylar) across each side of AC to ground (chassis), after the equipment fuse and at or before the power transformer primary. (These capacitors were for RF or transient suppression.) Sometimes, another capacitor was connected across the primary itself. The assumption at the time (even with the two prong non-polarized AC plug) that the equipment chassis was effectively grounded. With a power transformer, there was no reason to connect one side of AC to the chassis, unlike typical AC/DC gear built at the time. However, the transient suppressor capacitors from AC to chassis did "bleed" an extremely small amount of AC to the chassis, and someone would feel a shock, especially with a mike at the mouth. (The reactance of each .01 uF capacitor at 60 Hz is around 265 k ohms; the current through each capacitor with 117 volts applied is around 0.4 mA.) The obvious repair is to install a grounded power cord (3 conductor) to the amp, and make certain the receptacle ground is good. (If you are a "purist" and don't want to modify the amp, connect the chassis to an effective ground like a grounded METAL cold water pipe; there may be a ground post on the back of the amplifier for that purpose.)

The other scenario is a defective (leaky) power transformer short from a winding to the core. The core is essentially connected through the transformer case to chassis. This scenario could elevate the ungrounded chassis to a dangerous voltage. Again, the obvious need for a grounded power cord. With a grounded power cord, a shorted power transformer to chassis should immediately blow the equipment fuse, or your eyes and/or nose will lead you to the problem.

Yessir, that's correct. The only amp I still own like that is a '69 Super Reverb, and that's right - 1x GZ34 Rectifier tube, 2x 6L6GC Power tubes, and 6x assorted 7025, 12AX7, & 12AT7 pre-amp & reverb / vibrato driver tubes.

So this is basically what we're looking at, as you've described. I'm not adverse to putting a ground cord on it, but I am adverse to what they're asking for a genuine Fender cable. Ideally, I'd want to change out the receptacle on the back of the amp to a grounded version at the same time.

The days of me breaking my back lugging around an amp that size are behind me, and the days of traveling with a road-crew are waaaay behind me. So the '69 Super and I will probably both be comfortably planted here for some time, until someone is looking for that signature vintage Fender tone.