Need help to figure out this Noise!

[zedsnotdead]

Hello people!
Happy new 3013!!

Well, I just had a conversation with a buddy of mine and he told me he's got a problem with his amp.
It was noisy, but when he touched the strings or any metal part of the guitar and/or amp, the noise was almost eliminated.
He tried with different amps, different guitars, all noisy.

So one day he tried the amp on another division of the house, one with earth connection in the electric wall socket (is this how it's spelled?) and the noise disappeared.

Ok, so what's buggin' me is why in the hell did the noise also disappeared when he touched the metal parts (guitar or amp) when the amp was plugged in the wall socket with no ground connection?
What was causing the noise?
I mean, one could believe that it was a guitar shielding problem right? Like touching the strings, no noise... and so on... the usual right?

PS: forgot to mention, the amps he tried were all solid-state, no valve.

[sumgai]

zed,

Jan 1, 2013 19:56:48 GMT -5 zedsnotdead said:

Hello people!
Happy new 3013!!

Look me up in a thousand years, and if the amp is still noisy, I'll tell ya how to fix it!   (Though it's likely that the cost of any parts will just about kill ya!)


Seriously, what you describe is perfectly normal. The real problem lays in terminology. What you are doing when you touch the strings is to ground yourself, through the guitar, cable and amp, thus reducing the amount of noise that you're giving off.

I can hear you now - "me, give off noise?". Yes, you're the culprit. Your body acts like a big antenna, and when you're in close proximity to a pickup, you re-radiate that noise you've been collecting, and of course, it all goes right into that pickup. End of story there.

So what happens to make it quieter in another part of the house? Simple - it's the environment itself, not necessarily the fact that a socket may (or may not) be properly grounded. For sure, proper grounding helps, but it's more important that the you (the player) and your equipment are in a place that has little "free floating" noise to start with. Fluorescent lights are a major issue here, as well as motors, dimmer switches, and other stuff that might be plugged into a good solid ground, but may be completely unshielded, thus giving off "noise".

Your test methods were fine, you just needed to (and still need to, IMO) get completely out of that house, and set up somewhere else. Another house (yours?) or a local guitar store, or perhaps a work environment, the possiblities are unlimited because all you want to do is change the place of operation, for comparison purposes.

However, be aware that some folks, sadly, live in a large noisy zone. Under the powerlines qualifies here - no matter where in the house, or even in the house next door, you're gonna suffer, big-time.   Just think about it for a moment, and I'm sure you'll easily avoid that kind of thing, as you search for a test location.

Oh yeah..... shielding your (his) axe is the name of the game! ;D

HTH




sumgai

[zedsnotdead]

3013...
Sorry!! Happy 2013!!!! (that's right!)

sumgai, thank you so much for your reply, but I think you missed the point.
I know that one of the symptoms is pointing for lack of shielding. I mean, I know that our body is like a "antenna" capturing noise, and that we ground ourselves when we touch the strings (thus noise is reduced). I know that.

What bugs me is:
- the amp was not plugged to a grounded wall socket. But the noise disappeared when we touched any metal parts of the guitar (like bridge/strings) and/or the metal parts of the amp. It's a typical problem of lack of proper shielding, so shielding could solve or minimize the problem, so I thought...
- but then why did the noise disappeared when the amp was plugged to a wall socket with ground connection? He did no shielding to the guitar, just plugged the amp with a ground connection, so the problem caused by external EMI should still be there, right?

Now, I researched and googled for amp schematics. what I found (and I could be wong, please correct me) is that the grounds in the input transformer (AC/DC transfomer) are separate. The ground on the wall socket is mainly for the primary part of the transformer. The DC (secondary) part have it's own ground...
If this is true, the more confused I am....

[JohnH]

I couldn't explain it without making up some BS, so I wont try,.

But it seems reasonable to me that in a piece of gear seigned to be grounded, you'd get more hum if it is not grounded, since it would be 'floating' electrically. And touching the strings always reduces what hum is there.

But I would think that a good policy for a long as well as a happy life is to use properly grounded electrical systems - for safety.

John

[4real]

- the amp was not plugged to a grounded wall socket.

[glow=red,2,300][glow=red,2,300]WTF [/glow][/glow]

[zedsnotdead]

4real

Sorry for my english, it's not my main language and probably I misslead you.
What I meant is that the wall socket didn't have ground, only phase + neutral.
Something like this:


Also, there are solid-state amps that doesn't have a plug with ground connection. I remember my old Roland Cube, it didn't have any.

[newey]

zedsnotdead said:

Ok, so what's buggin' me is why in the hell did the noise also disappeared when he touched the metal parts (guitar or amp) when the amp was plugged in the wall socket with no ground connection?

A two-prong electrical outlet/plug lacks the separate ground of the three-prong type (called the "NEMA 5" standard, for those of us in North America). But that doesn't mean that it isn't "grounded".

"Ground" is a DC term that doesn't, strictly speaking, apply to one's household AC. In AC terms, we'd speak of "hot" and "neutral", and we recognize that the two "swap sides" 60 times per second.

But that doesn't mean that things aren't "grounded" or (better said) "earthed"; the "neutral" wire does double-duty in household AC. Ultimately, the chassis of one's amp is grounded in this way whether it's a two-pronged plug or a three pronged plug. The third prong simply adds an extra ground connection. This is important mainly for fire safety. It has nothing to do with levels of noise.

My suspicion would be that the circuit that was three-pronged was also just quieter. The way to test would be to plug back into the two-wire outlet in the noisy area, and start, one by one, eliminating electrical devices from that room, and also disconnecting things connected to that same circuit, even if the items are in different rooms. If it gets quieter at some point, you've found the culprit.

[sumgai]

zed,

I'll have to go with 4real's question - WTF? That must be one hellaciously old house your friend lives in.....

And John probably does know what's up, he's just playing the Modest Card this year.


As it happens, you're correct, I missed your intent. Sorry 'bout that.

So the real story, sans BS. The reason I said "old house" is because up until the late '60s (in the US, at least), the majority of houses were wired with only two wires to each socket, not three. The introduction of the third wire, supposedly there to ensure a good ground connection, thus protecting the user, came about because of prior wiring practices.

These practices dictated (that's the correct word!) that the White wire be tied to the Ground Buss in the distribution box, and the Black wire was to be Hot. Keep in mind that we're speaking of references here - the Black is hot compared to White, because we conventionally think of Ground as 0 volts (AC or DC). Also remember that it was called "ground buss" because it was more than just a common shared connecting point, it was (and still is) actually tied to a stake driven into the ground outside of the house. (Although sometimes the 'electrician' got away with using the water pipe entering the house close by the electrical box - "Hey, it's metal too, ain't it?". Bad juju. )

Now, if there are only two wires, and if one of them is ground, then we have a great potential for a problem, in fact two of them. First, what happens if the electrician is drinking on the job, and wires the sockets backwards? And second, what's to stop the user from plugging his device into the socket "backwards" - that is, what the device manufacturere intended to the ground side is now connected to the Hot side instead. ( ) This caused many deaths over the course of the first six decades of the 20th century, because most devices used a metal chassis. Why? Because metal was cheap, easy to work with, and most important, it carried electricity just fine, thus allowing it to become a conductor for one side of a circuit (chassis ground). Since many circuits shared a common point anyways, using a metal chassis made sense - it saved on wire material, the time to make a lot of connections, and it served as a giant connecting point for testing and troubleshooting.... the instructions were dead simple: "Place the meter's negative lead on the chassis". All wrapped up, nice and dandy.

Until people started plugging things in backwards. After about umpty-squat years, the lawyers ascended to power, and the threat of being sued out of existance caused sockets (and device plugs) to be built with different sized prongs. This is what we call a 'polarized plug', and it worked just like it was supposed to. Providing the electrician connected the sockets to the house wiring correctly, electrical-shock deaths dropped almost off the charts, numerically speaking.

Now, if that works so neatly, how come there's a ground? Simple: greed. Lawyers (sorry, newey!) saw a gravy train, and started - fully uneducated in the ways of electricity, mind you - to campaign for stronger safety standards. About the only thing left to do was to take the polarized plug and insert a third prong, what we know as the Ground pin. That was supposed to keep equipment from shocking people no matter how the socket was wired - "See, there's a bare wire right here in the cable, and it's grounded - see?!" Thus, if something went wrong, it was pretty close to a 100% certainty that the fault lay with the device, and not the house wiring.

(Parts of the preceeding have been glossed over for brevity. Obviously if it took 15 to 20 years to make it all happen, the story deserves more than a single paragraph to explain the details.)

But wait - I can hear it now - if the White wire goes to ground, and if there's a bare wire going to ground.... isn't that a Ground Loop?

Go to the head of the class, bunky! That's exactly what's happening, and exactly why we still have electricity-related "incidents". (They're no longer known as accidents. Call it PC for the feelings of the idiot who injured himself.) In point of fact, the difference in voltage between those two conductors does indeed allow for a small amount of noise to creep in, in the form of a very low voltage. And again, the lawyers came to our "rescue", and forced yet more safety, albeit under great duress - the result was the GFCI, or Ground Fault Circuit Interruptor. (Called by various names elsewhere on the planet, but the intent is the same.)

This is what we should've had in our houses all along, a way to automatically detect when a device is not connected correctly, and to then disconnect the main power from that socket. Alas, it does take time and energy to invent stuff, and one more thing - necessity. A hundred years ago, civilization considered an adult to be a reasonably cautious person, and to exercise all due care and caution where known risks were present. And in a nutshell, the Stella effect started about the first time a newly graduated Law Student couldn't find a job at a big firm, and went out looking for a windmill at which he could tilt.

The rest, as they say, is History.

Now, if that wasn't clarification enough, please don't hesitate to ask for more details. ;D

HTH

Summary:
In a two-wire socket, Hot and Ground may be reversed. This can, and often will, present itself as noisy equipment (and not just guitar amplifiers), and should be considered an extreme danger.

Worse, the socket could be correct, but if the device is plugged in backwards.....







sumgai



EDIT: Ninja'd by newey, but my dissertation still stands.

[4real]

Hmmm



Here is an RCD saftey switch power board. Here, most if not all houses have these, but regardless these are useful. If your power is dodgy, it will trip. Anything plugged into it will trip it so you can run your 'stuff' from it...then when you are using an electric saw to cut through the power cable for instance, you are less likely to die!...no dying is a good thing. (note also the Australian standard 240v AC standard plug with third ground prong...you can't plug it in backwards, eve if two prong!!!

Now, this will not solve your noise...but who knows wat else is running on this dodgy wiring for instance generating all kinds of power fluctuations and the like.

No...others are more knowledgable, but I ahd a lot of similar 'noise problems' with my guitar amp, computer and powered monitoring system as it 'grew'. The computer is a large laptop so could/can run off batteries and so can run 'out of the loop' and sure enough, not the power/noise problems there...but it will run for a bout 15mins at best.

To solve the problem, I have had to run two DI boxes. One an "HD400 behringer 2 channel Hum Destroyer" on the signal cables out of the USB powered (so, connected to the computer) Edirol UA-24 audio capture interface capture to the powered monitors. Usually though, I run the computer audio through a mini HiFi aux input which has no 'third prong' and so run that separtately without ground loop noise via RCA plugs without need for (and would not work either) through the DI device. Now, should I wish to run a 'direct line' out of my Fender valve HRD into an input into the audio capture...well then, I need another DI, for this I ahve an Behringer Ultra-G GI-100 powered DI single channel box which also has an option of 4x12 peaker cab simulation and ground lift and other features in it. Neither are very expensive and does the job and could be useful in a noisey environment.

Regardless, the whole house is 'saftey switch' protected and will trigger with faulty equipment or accidents...but I also use some of these power boards elsewhere, likely they will trigger first and not bring down the entire house power and other features will hopefully protect a little more against 'surges' and the like taking things out as well. Such a board can be really useful when you go play somewhere else and you don't know what their wiring is doing and to stay safe.

You can also get cheap power checking pugs that simply plug into your power points and test through a series of lights how the wiring is wird inside the wall. As a renter and a renovator in the past, such things can be really helpful and relatively cheap.

The guitar can be a particularly hazardous thing with electricity, the current is very likely to go through your arms and right across your chest...and therefore heart! Don't think it won't happen to you...it's happened to me and I am 'mr careful' generally...

[gumbo]

....add to all this the possibility of a 'dodgy' extension cord where 'hot' is not necessarily wired to 'hot' at the other end, and the list goes on....

...don't ask me how I know about THAT one....


As 4r says, a simple off-the-shelf AC tester is not an expensive item (at least here in Oz), and it certainly can save lives, let alone bags of inconvenience and/or heartache trying to figure out what is REALLY happening..



on topic, sg...... Sir!

[Deleted]

Jan 2, 2013 17:16:48 GMT -5 newey said:

zedsnotdead said:

Ok, so what's buggin' me is why in the hell did the noise also disappeared when he touched the metal parts (guitar or amp) when the amp was plugged in the wall socket with no ground connection?

A two-prong electrical outlet/plug lacks the separate ground of the three-prong type (called the "NEMA 5" standard, for those of us in North America). But that doesn't mean that it isn't "grounded".

"Ground" is a DC term that doesn't, strictly speaking, apply to one's household AC. In AC terms, we'd speak of "hot" and "neutral", and we recognize that the two "swap sides" 60 times per second.

But that doesn't mean that things aren't "grounded" or (better said) "earthed"; the "neutral" wire does double-duty in household AC. Ultimately, the chassis of one's amp is grounded in this way whether it's a two-pronged plug or a three pronged plug. The third prong simply adds an extra ground connection. This is important mainly for fire safety. It has nothing to do with levels of noise.

My suspicion would be that the circuit that was three-pronged was also just quieter. The way to test would be to plug back into the two-wire outlet in the noisy area, and start, one by one, eliminating electrical devices from that room, and also disconnecting things connected to that same circuit, even if the items are in different rooms. If it gets quieter at some point, you've found the culprit.

hmmm newey, you obviously know much more about electricity than i do, but at least in Greece he have three kinds of wall sockets :







could not find a proper photo for the 3rd case, but its two pole, without grounding.

Well, i had extreme buzz when plugging my amp to two pole socket. And almost no buzz with the first 2 types.

[zedsnotdead]

Jan 3, 2013 8:41:38 GMT -5 @pyrros said:

Well, i had extreme buzz when plugging my amp to two pole socket. And almost no buzz with the first 2 types.

yes, that's what happened.
And that's what I want to figure why.

First: even with that "two pole" connectionc, why did the noise disappeared when touching the metal part of the amp (e.g. the input jack outter ring), if the problem was lack of earth connection on the amp?

Second: for what I understand, the primary and secondary of the input transformer (AC/DC) have separate earths/grounds. Like this:


So it doesn't make sense because the ground is not dependable of the "earthed" wall socket this way.
Am i correct?

[sumgai]

zed,

I'm with ya, but right now I got people coming to take some measurements in the kitchen, and build some special cabinets for which I don't have the tooling.

I'll be back soon, so stay tuned!

In the meantime, your questions are valid, and there is an answer, although we may have to do some searching around for it.




sumgai

[jerry]

Induced hum due to electromagnetic fields (which is what we're discussing here) can be a bear to locate and understand. That's because hum (and other electric noises) can come from many different sources, such as the power line (mains), the human body, inductors (transformer cores, motor windings, or antennas), etc., etc., etc. So, most of the various suggestions of cause offered are correct. But determining your particular cause is difficult to do remotely through nothing more than a forum.

If you touch the signal lead of a guitar cord plugged into an amp with the volume turned up some, you'll hear the power line hum picked up by your body as an antenna. If you touch a grounded object with the other hand, the hum will often stop because the capacitance of your body bleeds the hum signal to ground.

In your case, the hum disappeared when you touched the guitar meaning that your body's capacitance took the hum signal to ground. Whether your body acts as the signal collecting antenna or the capacitor to ground depends on the EMF around your location, how your amp is designed and wired, whether proper grounds are available, and if so, used, etc. As I mentioned at the beginning of this response, the cause can be difficult to determine because we now live in a world bathed in electro-magnetic fields of power lines, many appliance motors and transformers, electronic gadgets, wireless devices, radio, TV, microwave broadcasts, microwave ovens -- the list goes on and on!

In some cases, touching your guitar, and simultaneously, a good metal ground, can actually be dangerous because your body is completing a path between some voltage and its return through the grounded item. Many of us older guitarists remember touching our lips to the metal screen on the front of a microphone (at a gig) while holding our guitars and getting a NASTY BITE (electrical shock) to our lips -- NO JOY! In the 60s and 70s (maybe later also), the chassis of many amps were electrically hot depending on how you plugged the cord into the receptacle. That is one reason the U.S. mandated the third wire on grounded plugs and receptacles mentioned by Newey.

Today, most amps are isolated, but I don't like every manufacturer's approach. I recently bought a Fender Acoustasonic that I love using. But when I added an additional switch to back of the chassis, I discovered that the chassis IS STILL HOT, but Fender puts a thin plastic insulating coating over it to protect the user. By adding that switch, I inadvertently defeated that protective scheme without much problem (a dubious talent). So when I touch this metal switch which touches the uncoated metal of the chassis, I'm electrically HOT (I tell my girlfriend that being hot is desirable, but she's on to my ways and doesn't believe me).

[4real]

Good Post J...

Many of us older guitarists remember touching our lips to the metal screen on the front of a microphone (at a gig) while holding our guitars and getting a NASTY BITE (electrical shock) to our lips -- NO JOY!

Absolutely, been there and worse. Actually I got a bit of a shok the other week touching an alesis midiverb that uses a AC/AC adapter...probably responsible for damaging my fender amp too if the truth be known!

...

My reaction might be excessive, we do live in a noisy environment especially these days. Sounds much like a ground loop problem, but it is of some concern when clearly one's body is the 'ground sink' and that the guitar is a perfect way of conducting current across the body and right through the heart!

With these 'tests' is it just the guitar and amp? No effects or other things in the signal chain? This an unmodified non-diy amp? Is the house possibly badly wired? I had no idea that in the USA it was perhaps possible to plug something in back-to-front, or am mis-understanding these things.

I wonder whether a DI would help...

I quite liked the look of those acoustisonics...it's disappointing when you hear about that kind of thing and wonder if something similar is happening with my effect unit...how would one test if a chassis is 'live' like that? It uses a 2 prong Ac/AC adapter at 9 volts.

[jerry]

I think the problem that Zed's buddy has is that amp is being used in a noisy environment as Sumgai has suggested. Touching a metal part of the guitar is grounding the noise signal. Moving to another part of the house solved the problem. I don't believe the fact that the receptacle in that portion of the house having "an Earth connection" has any part in the quieter operation of the amp. Rather, I suspect that portion of the house is less electrically noisy, so there's less for the amp to pick up. As I said, trying to diagnose such a problem without being there is difficult at best.

I don't think that a DI would help in this case. But again, without being able to trace the noise signal, what I don't know here is vast (in fact, I've learned that what I don't know in general, is vast...very sad...)

Regarding the Acoustasonic, it uses a 3-wire C-13 power cord. That's the same cord used for most computers, rack mounted equipment, etc.

There is actually a warning printed on the back of the chassis stating that it is hot -- I just never noticed it before I drilled the hole. I had no idea that any manufacturers were intentionally making a chassis hot and then insulating it from the user.

[JohnH]

Jan 2, 2013 17:29:06 GMT -5 sumgai said:

And John probably does know what's up, he's just playing the Modest Card this year.

No I really don't know. If I did I would have posted it.

Could be an electrical fault in the wiring
Could be a generally noisier electrical environment

Following is speculative: If these amps are designed with two pin power, and are therefore insulated so the chassis and touchable parts are nowhere near the mains wiring, and there is no ground pin anyway on the amp, then the amp isnt getting grounded any more in the quiter room. But maybe the existence of the ground circuit in that part of the building is helping to keep electrical equipment nearer to all being at the same potential instead of floating freely. With the human body being one of the biggest factors in guitar noise, when not touching, the body will be at some potential detrmined by the environment, the floor, the conductivity of your socks etc. The guitar and amp electronics will be at some other potential, not directly related to ground, but determined by its own wiring and emfs that it recieves. When you touch the strings, the body and amp ground circuitry become one, reducing relative voltages between them and so reducing noise. If insulation is correct, none of this involves significant current - its all very high impedance - but guitar amp inputs are high impedance, and with gain, small differences get amplified.

John

[sumgai]

zed,

I'll go with what Jerry said, I think he's nailed it pretty well. (Thanks, Jerry! ;D)

Check the environment first. The best way to do this is to pick up and move everything to a completely different environment. Short of that, it's still guesswork. ;P

---

Jerry,

I suspect that Fender didn't intentionally make the chassis hot, they just covered their butts by adding a warning label that it could be hot (compared to the surrounding environment). Like us, they have no clue how the amp will be used in the field, after it's left their hands. But you can be sure that if they didn't give some sort of warning, they'd be sued for some clown-user's stupidity, or just as bad, some clown-electrician's stupidity that the user could'n't've possibly foreseen.

---

4real,

I don't pay attention to what the wall sockets look like in other countries (check out this page for a nice overview of the world's different power connectors), but I can tell you that what we have in the USA today is, excepting the addition of the third pin for ground, exactly what we started with nearly a hundred years ago. IOW, a record player console or a radio from the late 1920's or 1930's would plug right in, and presumably work just fine. The polarized plug introduced in the late 1960s was made so that older appliances would still work without modifications, a sop to economics more than anything else.

And speaking of that, I have to admit that my history was a bit rusty, so I looked it up..... Patents were filed as early 1914 (in the USA) for polarized and grounded plugs/sockets, for the express purpose of safety. Economics determined their failing to take hold and become a standard. (Remember, this was before the days of government-sponsered over-regulation). My memory of the late 1960's being the time of introduction of our current setup may be off by a few years, but that's what I recall, anywho.

---

John,

No, I didn't doubt your veracity, I was simply being complimentary.   And your supposition is as sound as anything else said here on the topic, so you've proven my point. ;D


HTH




sumgai

[jerry]

Jan 3, 2013 16:32:32 GMT -5 sumgai said:

Jerry, I suspect that Fender didn't intentionally make the chassis hot, they just covered their butts by adding a warning label that it could be hot (compared to the surrounding environment). Like us, they have no clue how the amp will be used in the field, after it's left their hands. But you can be sure that if they didn't give some sort of warning, they'd be sued for some clown-user's stupidity, or just as bad, some clown-electrician's stupidity that the user could'n't've possibly foreseen.

Hey Sumgai,

Well, you could be right. The actual statement on the back panel is:

"CAUTION: CHASSIS SURFACE HOT"

So, I don't know what they truly did. However, your assertion that their warning is to protect themselves from liability is almost certainly spot on. For sure, there is a plastic coating on every place that the chassis is exposed outside the amp case; I first noticed it when I drilled the switch hole and found plastic turnings in addition to the metal ones. And every control is plastic, including the pushbuttons and rocker switch.

Next time I open the amp, I'll do some testing with my VOM and report back. It'd be good to know.

User stupidty??? Does that truly happen? :-)

Jerry

[sumgai]

Jan 3, 2013 17:42:41 GMT -5 jerry said:

User stupidty??? Does that truly happen? :-)

In my Army days as a technician, we had a form for users to send in with equipment needing repair*. On the back was a list of codes we were to enter for the fault(s) we found. I not only remember, but still use in my daily language, fault code 800 - "Operator Inefficiency".

I don't think the times have changed so much, eh?



sumgai






* For those of you who have been elevated to my level of judgability, that would be good ol' Form DA 2407 - Work Order and Request For Modifications. (In quadruplicate, of course.)