P90 PU's and noise - newb question

[stallik]

My first time using P90's and I'm getting that single coil noise which cancels when I touch the strings.  Noise is much greater than my Tele or Strat single coils. Is this expected behavior with P90's? or should I be doing a much better job of shielding cavities etc - something I've not had to do on the other guitars.
I'm reluctant to call this hum but there must be an official title for it.

iPhone analysis FWIW. Light blue - not touching strings

[GibsonGM]

I'm not the biggest gear-head so other opinions might vary, but they're kind of known for it, Stallik.  You could try shielding the cavity more, that may help, but I wouldn't expect any miracles. They say that's the price you pay for a great sounding pickup.   Maybe a kill switch could be useful?

[stallik]

Thanks Mike, that's what I was expecting but just wanted to make sure I wasn't missing a trick. I can work round the issue and, as you suggest, they do sound good

[iainpunk]

p90's are generally just noisier due to having more windings. a good ground connection can be a solution here, i would build a pedal thats just a through box, with an extra 'banana' jack on top, where you can plug in a long wire with a banana plug on one side and a crocodile clip on the other, so you can physically clip to a grounded point, like a radiator or other water pipes. i have an extension cord that adds a ground wire for when the wall contacts don't have a ground plug, but it feels a whole lot jankier that way.

cjeers

[stallik]

I'm really wondering about the grounding on this guitar. Don't get me wrong, the ground connections are all secure, bridge is properly grounded, jack is fine and my pedals / amps give no such issues with other guitars. It's the pickups themselves that I'm suspicious of. Because I really like the dynamics afforded by the output of my last humbucker build, I ordered some overwound P90's trying to get close to the same output level. The P90's are very nicely made but the wiring is vintage style cloth for the + and a bare thick screen for the -. Not at all sure if any metal parts of the PU are attached to ground so that's something I'll have to check out.

That will wait till after the holidays. I'm enjoying playing it at the moment. More than any PU type I've played, these things give the fattest tone with loads of gain and the guitar volume rolled right back. Completely addictive. And the noise only happens when I let go. Taking one sock off and touching the cable jack with a toe works fine if needs be

[anotherjim]

I've heard you can overdo pickup cavity shielding. If it goes all the way up to the top, it can cut treble response. Not sure how. Could be eddy currents in the shield from the magnet circuit wobbling when the string vibrates I suppose. Maybe screening paint might be better than copper foil in this regard?

[iainpunk]

maybe get yourself an anti-static wrist band to connect to the guitar's ground

cheers

[GibsonGM]

I'd make a joke about running wires from the amp's trafo out to a box with lugs to put your toe on, but you never know - someone casually passing thru might try it!!!     

You might explore whether the PU cases are connected to ground...but you know they probably and that's just how they are. After the basics are eliminated, I think we're stuck with what we've got! 

[pinkjimiphoton]

p90's sound great, but they are about 3x as noisy as a strat or tele. its big coils, with a lot more turns on them. shielding helps a little, but the only thing i ever found to work was just turning down the volume pot on the guitar slightly.
i ride my volume all the time, but if i didn't, it would be noisy as hell when i use my p90 guitars.

[Mark Hammer]

I concur with Jimi.  One of my guitars has a P90 at the bridge and a single coil I wound myself at the neck.  The bridge P90 is noticeably hummier than the neck SC, and not because I did any fancy juju.

[PRR]

cancels when I touch the strings

When your body is grounded. YOU are the buzz (overtones).

[pinkjimiphoton]

yep. what paul said. YOU are literally a biological antenna. you're picking up radio waves, television broadcasts, russian hackers <g>, you name it. maybe alpha centauri or the borg collective.

when you touch a ground point or any metal connected to a ground point, you magically shunt all this noise your body poots forth straight to ground and the buzz goes away.

completely normal, and yes, it will be way more noisy as the level of gain or distortion increases.
i explain this to guys on guitar forums constantly, while the snake oil salesmen try and get them to pay for rewiring jobs and stuff they don't need.

turn your guitar off when you're not playing it. keep a hand on it while you are. problem solved!

[stallik]

How succinctly put Paul. And provably correct of course.

Mr Pink, I like the phrase biological antenna. Fortunately, mine's not picking up radio.  Now I know that P90's are noisier, I'm completely happy that I've not screwed up and, as you say, it's not hard to work round the issue.

I will shield the cavities when I've completed the finish but that's really for completeness. I don't expect it to improve things much

Happy Holls guys

[pinkjimiphoton]

[Rob Strand]

My first time using P90's and I'm getting that single coil noise which cancels when I touch the strings.  Noise is much greater than my Tele or Strat single coils. Is this expected behavior with P90's? or should I be doing a much better job of shielding cavities etc - something I've not had to do on the other guitars.
I'm reluctant to call this hum but there must be an official title for it.

Technically it's capacitively coupled interference.  Where "interference" means an unwanted signal vs "noise" which is from a physical noise process.  For conversations I still call the interference noise.

The way to think about it is there's a small capacitance between the noise in the outside world and the wires on the pickup and guitar.   The reason the "noise" sounds buzzy is because the capacitive coupling acts like the cap on a high pass filter which emphasizes the higher frequencies of the noise.  When you play the guitar your body couples more noise into the guitar because your body has a large area.  Any ungrounded metal around the pickups can work in a similar way.  When you touch the strings the noise on your body is passed down the ground.  Not only that, your body acts like a shield and blocks noise from getting to the pickup.

You need to treat each end of the pickup wiring differently.   Noise coupled to the ground side of the pickup wiring will be diverted to ground.   Noise coupled to ungrounded wiring will inject noise into the signal path.

Suppose the pole pieces aren't grounded.  If you ground the pole-piece side of the pickup winding (the winding start) noise couples to the pole-pieces (a metal area) then across to the winding start  but is then diverted to ground.   The outer surface of the pickup windings has a large exposed metal surface.   Noise couples to this large area and since it isn't grounded the noise goes straight into the signal path.   By shielding and grounding the pickup cavity it prevents noise coupling onto the outer surface of the winding.

If you have the outside of the winding connected to ground and the winding start connected to the signal then it's harder to block any noise getting on *ungrounded* pole pieces.    So for ungrounded pole pieces it usually better to ground  the winding start.

If the pole pieces are grounded then the pole piece will act like a shield, and if the pickup cavity is also shielded you might find you can connect the pickup either way and both connections will be noise free. 

As you can see there's lots of combinations but they can all be deciphered.  Without shielding the pickup cavity something always ends-up being exposed and noise will couple in.   The fact we can touch the strings and shut things up is good but the fact the noise is there when we let them go means things aren't great in terms of shielding.

[iainpunk]

... Mr Pink, I like the phrase biological antenna. Fortunately, mine's not picking up radio. ...

...I will shield the cavities...

yes some filled cavities with the vintage metal fillings will actually demodulate strong FM signals.

https://www.bradfordfamilydentist.ca/lucille-ball-heard-spies-dental-fillings/

cheers

[PRR]

Yes, high-tone buzz because of capacitive coupling working better at higher frequency. Put a pickup on top a large power transformer you get the deep humm.

It's not inevitable. You can't pick-up what isn't there. I could go back in my north woods with a battery amp and get no 60Hz at all--- no power line for a mile each way. Hardly any AM radio neither. (The tower on the far side of the bay may have more watts in its anti-airplane lights than its transmitter.... the next big rig is Boston which is hard to catch here on a real radio.)

[sekim]

Depending on how much effort you're willing to go to and how much room in the guitar you have to work with, you might try the approach Fender uses with their noiseless Strat pickups. They do dummy coils on the underside that are wired as humbuckers. I have a set in a Strat and they definitely sound like Strat pickups with no noise.

If space is tight, it may be that enough windings for a dummy coil could fit in the available space that it doesn't fully cancel the P90 noise, but does reduce it enough to be worthwhile.

[pinkjimiphoton]

Depending on how much effort you're willing to go to and how much room in the guitar you have to work with, you might try the approach Fender uses with their noiseless Strat pickups. They do dummy coils on the underside that are wired as humbuckers. I have a set in a Strat and they definitely sound like Strat pickups with no noise.

If space is tight, it may be that enough windings for a dummy coil could fit in the available space that it doesn't fully cancel the P90 noise, but does reduce it enough to be worthwhile.

doesn't HAVE to be a p90, either... a coil from a tele or strat MINUS THE MAGNETS will work, too.

[Mark Hammer]

And while dummy coils will usually work best directly adjacent to the string-sensing coil, such that they detect the same amount of EMI when facing any particular direction, they can also work when located elsewhere on the body, like the control cavity, or in the case of the Suhr/Ilitch backplate on the back of the guitar.