Reversing a pickup on the Casino to reduce the hum? We had bad interference last night.

[Notes_Norton]

I have never been bothered by the slight hum of the P90 pickups until last night.

 

We played on a stage that had some kind of interference that both my Casino and Leilani's Parker with the coil taps pulled out (single coil setting) picked up and amplified.

 

The buzz was very loud, definitely 60Hz with harmonics and unacceptable. We tried turning off all the lights we could, plugging the line conditioner into different outlets, and nothing worked. I have no idea what was causing the interference.

 

Fortunately Leilani's Parker with the coil taps pushed in turns the single coils into humbuckers, and that quieted her guitar, but there was nothing I could do to quiet the Casino.

 

Since Leilani plays rhythm and I play lead, we switched guitars, the Casino unplugged with a mic in front of it, not the best situation but doable. I had fun playing the Parker, and although I missed the P90 sound, the audience is less particular than I am. But I missed Leilani's parts as they were not really loud enough. Although the Casino is an acoustic guitar, it does have a small box so it isn't very loud.

 

So I am wondering, if I reversed the polarity of one of the Casino P90s, and turned both pickups on, would it act like a humbucker? I of course would only use it if this situation arises again, and the guy who booked us said he would definitely have us back, so I might run into this situation again.

 

If reversing one would work, what would be the best way to do it. Is there a switch available that could reverse and/or un-reverse the pickup whenever I wanted to?

 

I hope I'm getting my point across, as I'm inexperienced at modding a guitar.

 

Any other suggestions?

[charlie brown]

Bob, just get a "noise gate" pedal....or two...one for each of you. Or, replace your P-90's with Stacked P-90's (SP-90) that Duncan makes.

But, the noise gate should do the trick. That way, you don't have to do anything to the guitar.

 

Oh...and didn't you say you had one of those "Digitech" (or some other brand) floor processors?

If so, it may have a "noise gate" built into it, that you can access. Just an idea...

 

CB

[Notes_Norton]

Bob' date=' just get a "noise gate" pedal....or two...one for each of you.<...> [/quote']

 

Sounds great. I'm familiar with using a noise gate for recording, but it definitely isn't set up for guitar. Can you recommend one? Would I put it before or after my FX/Direct-Box/Amp-Simulator pedal?

 

Thanks,

Notes

[Notes_Norton]

Will this do?

 

 

Link: Berhinger Noise gate - about $30

 

I don't want to buy more than I need for the occasional gig.

 

Notes

[Vic Flick]

I have never been bothered by the slight hum of the P90 pickups until last night.

 

We played on a stage that had some kind of interference that both my Casino and Leilani's Parker with the coil taps pulled out (single coil setting) picked up and amplified.

 

The buzz was very loud' date=' definitely 60Hz with harmonics and unacceptable. We tried turning off all the lights we could, plugging the line conditioner into different outlets, and nothing worked. I have no idea what was causing the interference.

...

 

So I am wondering, if I reversed the polarity of one of the Casino P90s, and turned both pickups on, would it act like a humbucker? I of course would only use it if this situation arises again, and the guy who booked us said he would definitely have us back, so I might run into this situation again.

 

If reversing one would work, what would be the best way to do it. Is there a switch available that could reverse and/or un-reverse the pickup whenever I wanted to?

 

....

 

Any other suggestions?[/quote']

 

Notes, there's a difference between reversing polarity and wiring the pickups out of phase. I think you're talking about out of phase with a coil tap switch, which is possible if the pickups are wired with two leads and a ground wire. But I don't think that would help that much, and the tone would be thin and hollow.

 

Polarity refers to the winding of the coils, North to South. The two coils on a humbucker are reverse wound, i.e. one is N-S the other S-N. That's what cancels out the hum. Most modern pickup manufactures will reverse the windings on one of the P-90s to achieve a similar effect.

 

One of the best examples is the Stratocaster. The middle pick up is reverse wound, so when used in conjunction with the neck or bridge pickup (positions 2 & 4) it will reduce the hum. But it also sounds a bit different, what some people refer to as the Stratocaster quack. Likewise, P-90s will take on a slightly different color to the tone if one is reverse wound.

 

Bottom line, you would really have to buy a set of pickups that are reverse wound, so I would suggest the noise gate first. I haven't gigged since last century, so I'll let others recommend which ones are good.

[charlie brown]

 

Sounds great. I'm familiar with using a noise gate for recording' date=' but it definitely isn't set up for guitar. Can you recommend one? Would I put it before or after my FX/Direct-Box/Amp-Simulator pedal?

 

Thanks,

Notes[/quote']

 

Well, I think all the manufacturer's of decent pedals have one. I use a "Boss," and I know Marshall makes one,

or used to, anyway. Best thing to do, if you can, is go to a GC or Sam Ash, etc., and try one or more of them

out. Have you checked your "direct FX" floor processor? It may have one, built in?

 

CB

[sjtalon]

For noise, somewhat hum cancelling, one single coil has to be reverse wound AND reverse polarized in relation to the other.

 

 

To RW/RP a pickup has NO effect on the tone of the pickup, all other things being the same.

 

Stratocasters get their quack from the locations of the pickups, relative to one another. Few Fender Strat model pup sets have a mid RW/RP pup, and some Fender Strat pups are identical in mfc. spec. to one another ( like the 57/62's).

[bluesman345]

My tech wired the P90's in my ZBD to be out of phase when all 3 pups are "on". For some reason (wiring), he said that he was unable to wire the 2 P90's on my LP GT out of phase. I play in a situation where there is LOTS of noise and interference from fluorescents, dimmers, etc. So far, the most effective thing that I have tried is the ISP Decimator Noise Reduction pedal. When you find the "sweet spot", it will get rid of as much noise as possible. Too much, however, will totally cut off your sound! The ISP is expensive ($170 CAD), but the sales staff I dealt with owned one himself and he said that it is the best on the market. Other than that, I have heard some very positive things about Behringer products, considering their very reasonable price point. Good luck...

[duane v]

I have never been bothered by the slight hum of the P90 pickups until last night.

 

We played on a stage that had some kind of interference that both my Casino and Leilani's Parker with the coil taps pulled out (single coil setting) picked up and amplified.

 

The buzz was very loud' date=' definitely 60Hz with harmonics and unacceptable. We tried turning off all the lights we could, plugging the line conditioner into different outlets, and nothing worked. I have no idea what was causing the interference.

 

Fortunately Leilani's Parker with the coil taps pushed in turns the single coils into humbuckers, and that quieted her guitar, but there was nothing I could do to quiet the Casino.

 

Since Leilani plays rhythm and I play lead, we switched guitars, the Casino unplugged with a mic in front of it, not the best situation but doable. I had fun playing the Parker, and although I missed the P90 sound, the audience is less particular than I am. But I missed Leilani's parts as they were not really loud enough. Although the Casino is an acoustic guitar, it does have a small box so it isn't very loud.

 

So I am wondering, if I reversed the polarity of one of the Casino P90s, and turned both pickups on, would it act like a humbucker? I of course would only use it if this situation arises again, and the guy who booked us said he would definitely have us back, so I might run into this situation again.

 

If reversing one would work, what would be the best way to do it. Is there a switch available that could reverse and/or un-reverse the pickup whenever I wanted to?

 

I hope I'm getting my point across, as I'm inexperienced at modding a guitar.

 

Any other suggestions?[/quote']

 

Probably just an isolated incident...

 

There was a club out in North Hollywood (FM Station), that would produce some interesting tones out of amps8-[ .... Probably should have worn a ESD on my wrist, because it wasn't unusual to shock your lips on the mics when playing at that club.

 

I would say if the issue continues, have the pups and the wiring checked.

[bluelake07]

Lindy Fralin is now selling a hum-cancelling P-90; they're going for $120 each, though.

 

http://www.fralinpickups.com/p90s.asp

[matiac]

Noise gates are great for your guitar, but another possibility could be the sound at the particular house you were playing at, if thats the case, a noise gate is a waste of time. I used to jam at this friends house, and his neighbor was a CB radio nut, and every time that guy keyed his mic, he'd bomb right in with whatever we were playing at the time, and the amp I had at the time (Peavey Mace) would pick up all kinds of shortwave stuff, the most memorable was a station that to us sounded Russian, plain as the nose on my face. My rig at the time was the aforementioned Peavey, an old MXR Distortion plus, Arion Stereo Delay. That was miked into a Pretty large PA thats too involved to go into right now, but I'm thinking the interferance was because none of the equipment was shielded, if a cop drove by and talked on his radio, we'd hear him.

[Axe2Grind123]

Probably should have worn a ESD on my wrist' date=' because it wasn't unusual to shock your lips on the mics when playing at that club.[/quote']

 

LOL I remember playing at a place like that, I remember thinking the $$ they were paying us was not worth the risk or death by electrocution.

 

Anyway the massive hum probably means the place is not wired correctly, thus the 'ground' prong on your power cable is not doing anything. You could rig an improvised ground but who wants to go through the trouble? +1 to having a noise gate on hand, and only use it when necessary...

[shartom]

I always carry two guitars to evey gig, one with single coils (56 Gold Top with P90's, or a 65 Tele) and one with humbuckers. Even with humbuckers, you can still pick up some hum. I was doing a gig last month and I was positioned right in front of the light dimmer. My Gibson LP Studio picked up some hum. I played the same gig last week with my Sheraton. Totally quiet.

I don't think all humbuckers are created equal.

Whenever I sing, the guys tell I should learn to hum.

[Notes_Norton]

Probably just an isolated incident...<...>

 

I'm sure it is. And I am assuming that it has something associated with the place I was playing. Especially since it happened to Leilani's guitar in the single coil mode and my guitar at the same time. What are the odds both guitars broke at the same time?

 

Since the guy who booked us told us we will definitely be back, I want to go for the cheapest and easiest fix I can.

 

I might try the pedal and before going to the gig, re-string my ESP which I almost never play (it has humbuckers) and bring it along for insurance.

 

We got the ESP on a deal we couldn't refuse, it is light, has a great neck, but I'm really not wild about the sound. I have some future dream of learning to play slide and using it for that. But I have to learn a lot more about "normal" guitar before jumping into slide.

 

Notes

[carverman]

My tech wired the P90's in my ZBD to be out of phase when all 3 pups are "on". For some reason (wiring)' date=' he said that [b']he was unable to wire the 2 P90's on my LP GT out of phase[/b]. I play in a situation where there is LOTS of noise and interference from fluorescents, dimmers, etc.

 

Thats probably due to the fact that the standard P-90s are wound in phase and only have one hot wire

and a shield, so no matter what you do with the neck/bridge, you aren't going to cancel hum. The only

way to do that is to open up the P-up on the neck (or bridge) and find the start/end of the actual coil

and reverse them there for reverse polarity and even then, flourescent dimmers are still going to wreak

havoc on the sound.

 

Some p-90 manufactures (GFS mean 90s) are specifically reverse wound (bridge) so that

when you combine both p_ups, you get some hum cancelling, but even that is not going

to help you with light dimmers.

 

Flourescent dimmers create a lot of noise that gets into the amp circuits and the only way around that

is a descrete noise filter...rf filter....

 

Years ago, I worked in a recording studio that had heavy duty dimmers and those created a lot of

interference. We had to install commercial noise filters and even then had to either turn them off

or turn them on full during sensitive low noise recording.

[Mugs]

Poorly shielded (cheap) guitar and effect cords, and poorly shielded internal guitar tone/volume circuits, can also 'pick up' "RF" and 60 cycle hum,-as can loose jack-nuts on effects pedals (they sometimes are designed to ground some circuits to the pedals own case and it can get noisy if they're loose)....

Yup, a noise gate pedal should be in your 'gig-hardware box' with the other 'backup' essentials-extra strings, cords, your tuner, batteries.

-a used or new 'Boss' noise gate has been the best I've found,-durable, effective and cheap (used), behinger might also be good given how well they actually copy boss designs.... there exists a slight 'noise-gate learning curve' to get best results-but no more so than any other 'pedal'...

Oddly, there are a couple worthwhile inexpensive things one can buy at 'radio shack', one is an "RF Line filter"(read the directions) -a device that plugs into the wall outlet, before all of your other 'outlet strips' and such,...it will alleviate some of the house line-noise, depending on what the source is,-but not all of the noise-(nothing will 'do it all' )-..

The other 'essential device' is a little "wall-plug"-looking "Circuit tester"-an inexpensive but well made by "Micronta" thing, with 3 rows of various colored LEDS that you plug into the wall for a 'readout' of the correctness-or not- of 'house' wiring,-it does a genuine 'ground and polarity check'-(definitely read the simple directions) perhaps saving a life, or at least a lip-burn, in advance of any kind of microphone/guitar 'shocks'-

Eventually, as 'single coil connoisseurs', we learn to position ourselves/equipment for playing, in such a way that after doing whatever above stuff, we aren't letting the pickups be close to the amplifiers own transformers, any AC lines, wall mounted rheostats (ceiling fans and lights use these) beer signs, neon, fans/motors, fluorescent lights, video games, computers, pin ball machines- ALL of these can be the source of mystery noise nightmares whether in-line, or ambient..

ok, now have fun.

[Notes_Norton]

I'm aware of the lights, dimmers, position of the guitar, different electrical circuits, and my line conditioner does have a very good line noise filter. Normal hum I can either minimize and/or deal with.

 

This was very abnormal. We tried turning off all the lights (we set up when the room was empty), getting out the extension cord and trying other outlets, and all the normal stuff. I have no idea what could have been causing the hum.

 

------

 

On a different but related subject. I once played outdoors at a grand opening to a new office building right next door to an AM radio station. The AM radio came through the telephones in the building and just about everything else, including our PA set. Remembering some electronics I had in school, I got out a pair of jumper cables, hooked it to the ground of the PA set and the other end to a copper water pip bib. Instant radio station removal. My wife thought I was a genius at that point in time.

 

------

 

So I don't hijack my own thread, I'll get back to the subject.

 

Is there a 60Hz filter available that can be put in-line between the guitar and amp?

 

Could a ground lift cable help?

 

Or an isolation transformer?

 

Just thinking out loud here. I think I'm going to bite the bullet on the Berhinger noise gate.

 

Notes

[Vic Flick]

For noise' date=' somewhat hum cancelling, one single coil has to be reverse wound AND reverse polarized in relation to the other.[/quote']

 

If you read my post, I did say "...one is N-S the other S-N." Is that not what reversed polarized means???

 

 

To RW/RP a pickup has NO effect on the tone of the pickup' date=' all other things being the same.[/quote']

 

Partially true, partially debatable. All things being equal, the pickup will sound the same whether it's RWRP or not when it's used by itself. In fact, there's no such thing as an RWRP except in relationship to another pickup. It's when you combine it with another pickup that things get questionable. Some people say no dif, some say there's a little difference, others will claim a major difference. It's like the argument about removing the covers from a humbucker, or do good quality capacitors make a difference in tone. It's a matter of perception, and if someone hears a difference, it's kinda silly arguing that he doesn't.

 

And any time two pickups or coils are used together, they will impact on each other. The most obvious example of that is the hum reduction you get when one of the coils is RWRP!!! Now it's possible that the perceived difference in tone some hear might just be due to the lack of hum. Remove the hum from the mix, and you're going to hear things differently. Maybe the hum is blocking out some harmonics/overtones and when you remove the hum, those become more out front. Or perhaps since the north is up on one pickup and south is up on the other, the proximity of the reverse magnetic fields cause them to slightly interfere with each other.

 

I'm sure that you know why Gibson used slugs on one coil of the humbucker, but I'll relate the story as an example of the effect of coils on each other for the rest of the board members who might not know. I find it rather interesting and somewhat to the point we're discussing. The designers perceived one coil being dominant and the second coil's primary function being noise reduction. So in order to down play the tonal properties of the second coil, the used flat slugs and kept them under the metal cover. The screws of the other coil were not covered and closer to the strings allowing it to dominate. That's why people started removing the covers, it opened up the second coil, and with some minor adjustment (lower the screws on the one coil & raise the pickup), you can get a better balance between the two coils. Think of a Gretsch Filtertron, both coils with exposed screws, perfectly balance between the two coils.

 

Stratocasters get their quack from the locations of the pickups' date=' relative to one another. Few Fender Strat model pup sets have a mid RW/RP pup, and some Fender Strat pups are identical in mfc. spec. to one another ( like the 57/62's). [/quote']

 

The vintage series uses the non RWRP pickups, the modern American Strat uses RWRP. I think the Deluxe series uses the noiseless.

 

Now think about it, why would they not RWRP the 57/62 vintage pups if all things were equal??? To preserve the vintage hum??? Or maybe it has something to do with the vintage tone???

 

 

 

 

 

Having an RWRP middle pickup will give you hum canceling when you are in position 2 and 4 on your strat. This is great for strat players that need to crank the gain from time to time or for people that play gigs in clubs with florescent lighting. The drawback of RWRP is that when it cancels the hum it also cancels musical tones and thins down your sound. Most people that play a strat never ever use positions 2 and 4; ever wonder why? If you don't get and RWRP middle then you won't have hum canceling in 2 and 4 but you will have a nice, smooth, full tone that most people really like. Rock Monkey Pickups UK

 

The '62 set utilizes slightly larger diameter Alnico 3 grade magnets than the VS set. They have a calibrated vintage magnet stagger that is reminiscent of the 60's Strat pickups They're wound with correct gauge Formvar Magnetic wire to approximately 6.2K ohms for all three pickups. The '62 set is also non RWRP in order to retain it's vintage vibe. Amalfitano Custom Hand Wound Guitar Pickups

[Axe2Grind123]

ho hum

[Vic Flick]

I'm aware of the lights' date=' dimmers, position of the guitar, different electrical circuits, and my line conditioner does have a very good line noise filter. Normal hum I can either minimize and/or deal with.

 

This was very abnormal. We tried turning off all the lights (we set up when the room was empty), getting out the extension cord and trying other outlets, and all the normal stuff. I have no idea what could have been causing the hum.

 

[/quote']

 

Notes, I was thinking about your problem and I had a thought. You would need a knowledgeable tech, but why not add a dummy coil to the Casino. It what Gibson did with the Blueshawk to reduce P-90 hum.

 

Basically, you take a P-90 and remove the magnet & slugs, leaving only the coil. Wire it to the circuit in series but reversed. For proper hum reduction, it should be physically parallel to the other pickups, but being hollow, there's plenty of room to mount it inside the body (it doesn't have to be exposed so your guitar would look the same). You can hook it up with a mini toggle so you could turn it on or off. That way you can engage it when needed (it will color the tone slightly), but also allow you to keep the original configuration as well.

 

Just a thought.

[carverman]

I'm aware of the lights' date=' dimmers, position of the guitar, different electrical circuits, and my line conditioner does have a very good line noise filter. Normal hum I can either minimize and/or deal with.

 

This was very abnormal. We tried turning off all the lights (we set up when the room was empty), getting out the extension cord and trying other outlets, and all the normal stuff. I have no idea what could have been causing the hum.

 

------

 

On a different but related subject. I once played outdoors at a grand opening to a new office building right next door to an AM radio station. The AM radio came through the telephones in the building and just about everything else, including our PA set. Remembering some electronics I had in school, I got out a pair of jumper cables, hooked it to the ground of the PA set and the other end to a copper water pip bib. Instant radio station removal. My wife thought I was a genius at that point in time.

 

------

 

So I don't hijack my own thread, I'll get back to the subject.

 

Is there a 60Hz filter available that can be put in-line between the guitar and amp?

[/quote']

 

You cant use an inline. RF interference and dimmer switching "hash" is all over the

place in the frequency spectrum. Most dimmer filters are just a coil of wire around

a ferrite toroid (ring). Generally these are effective to some degree, but you may

need a capacitor to ground (u-ground) and that has to be inside the amp. Generally

speaking two .01 400v caps from hot and neutral to ground effective reduce the

switching noise. The 60hz or 120hz hum (depending on the rectifier used) will be

smoothed out by the dc filter electrolytics. Some amps also use dc on the filaments

to reduce hum.

 

Guitar pickups are high impedance by nature, so you can't put an passive inline

filter in the guitar cord output and the amp input because it will affect the sound

quality. Les Paul used a low impedance pickup (150 -300 ohms impedance) to

get around that, however these are not readily available. You can use specially

designed balance transformers at each end of the guitar cord to eliminate some

of the noise picked up by the cord.

 

The Les Paul recording Lp used a Gibson impedance matching inline transformer

that is similar to a Shure microphone impedance matching transformer..

here is some info on that...

http://jbwid.com/guitar/lpp01.htm

 

you can get reasonable cheap shure inline impedance matching transformers

to cut down some of the noise..as long as the amp has the noise filters on

the a/c. here is some info on those..

 

http://www.godirectmusic.com/product_info.php?products_id=202

 

 

Could a ground lift cable help?

it depends on the source of the noise, sometimes it helps, but then you

are left without a protective ground and that's probably not wise due to

electrical shocks between mics and amps and guitars.

 

Or an isolation transformer?

again, it depends on where the noise is coming from...if it's noise from a A/C compressor

or something that produces RFI (radio frequency interference), it will go right through

the isolation transformer..which are very expensive btw.

 

Just Notes

[Notes_Norton]

Thanks to all, I'm learning a lot here.

 

That LTD we picked up for a song is getting more and more attractive as things get more and more complicated ;)

 

I decided not to modify the Casino. For one gig out of a few hundred, it isn't worth it to take a chance on changing the tone that I love so much.

 

On the other hand, I don't mind messing with the LTD. It's a cheap guitar and actually, I'd like to put coil taps on it and change the color (I'm not a fan of all-black guitars). But I'll probably just bring it along to that gig for insurance. I'll never get the time to sand it down and re-paint it.

Notes

[sjtalon]

Wow notes, those pickups really do start some buzzing ;)

 

 

This statement, :

 

>For noise, somewhat hum cancelling, one single coil has to be reverse wound AND reverse polarized in relation to the other.<

 

was to comment on Notes post

>So I am wondering, if I reversed the polarity of one of the Casino P90s, and turned both pickups on, would it act like a humbucker? <

 

 

 

 

----------------------------------

 

 

 

jerrymac posted :

>One of the best examples is the Stratocaster. The middle pick up is reverse wound, so when used in conjunction with the neck or bridge pickup (positions 2 & 4) it will reduce the hum. But it also sounds a bit different, what some people refer to as the Stratocaster quack.<

 

 

My next post was in the disagreement that, on the subject of noise canceling and RW/RP, a Stratocaster's "quack"

has nothing to do with RW/RP.

 

Vintage tone, vintage hum, keeping it authentic, sets with a RW/RP middle pickup, sets without, whatever, I'm just saying position 2 and 4.........quack is always going to be there. If it's and American Strat or MIM, a duck is a duck.

 

 

jerrymac, good explanation on the Gibson deal.

 

 

All and all an interesting discussion.

[Notes_Norton]

<...>All and all an interesting discussion.

 

 

I agree, I'm learning a lot here.

 

Since this only happened on one out of a few hundred gigs, I think I'll just re-string the LTD and bring it along next time we are on this particular stage.

 

I don't really like the way the LTD sounds, but that's a personal thing. For as many people in the audience who think the P90s sound better, there are probably as many who think the LTD humbuckers sound better, and the majority of them won't even know there is a difference.

 

I just hate to pack two guitars as I already have enough gear to schlepp:

* 2 wind controllers

* 2 guitars (Parker & Epi)

* 4 synth modules

* 1 sax

* 1 flute

* 1 Buchla Thunder tactile MIDI controller

* 1 Korg Pad Kontrol

* 1 rack with mixer, sonic maximizer, FX

* 1 rack with power amp

* 1 line conditioner

* 2 15" speaker cabinets

* 2 small monitors

* and mics, cables, stands, and so forth

 

But you gotta do what you have to do!

 

Notes

[carverman]

 

Notes' date=' I was thinking about your problem and I had a thought. You would need a knowledgeable tech, but why not add a dummy coil to the Casino. It what Gibson did with the Blueshawk to reduce P-90 hum.

 

Basically, you take a P-90 and remove the magnet & slugs, leaving only the coil. Wire it to the circuit in series but reversed. For proper hum reduction, it should be physically parallel to the other pickups, but being hollow, there's plenty of room to mount it inside the body (it doesn't have to be exposed so your guitar would look the same). You can hook it up with a mini toggle so you could turn it on or off. That way you can engage it when needed (it will color the tone slightly), but also allow you to keep the original configuration as well.

 

Just a thought.[/quote']

 

This is becoming quite an interesting exchange. The dummy coil needs to be in close proximity to the

pickup coil,...otherwise it's just going to pickup some additional noise on it's own. I thought that the

Blueshawk had the dummy coil in the actual tone circuit along with the range of caps.

Didn't we have the discussion on that topic back awhile ago, I seem to recall?

 

Humbucking could be considered a black art. Somebody has come up with a retrofit humbucking coil

for Strats but it also involves some resistor adjustments for balance. Slapping just a coil of any

value isn't going to be that effective to reduce common mode noise pickup.