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Easy P-90 hum cancelling mod Simple mod to put two P-90's in hum cancelling mode on center posi

#1 User is offline   Brickster86 

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Posted 30 September 2010 - 11:32 AM

Forgive me if this has been answered 1000 times, but I bought a '56 Goldtop with P-90's this summer. I love the guitar in every way, except that the 60 Hz hum is excessive (I am unlucky to have power lines close enough to my house that seem to get picked up quite well by the pups). Anyway, after searching for all sorts of fixes on the web, it seems that converting one of the pups to a reverse wired, reverse polarity was the answer. However, every post talked about swapping wires (i.e. cutting and/or resoldering) on the pickups. I was not interested in that so I figured there had to be a better way. There is, and it's easy. I did it last night, but unfortunately, I didn't take pictures. I think you'll be able to follow it anyway. It took me about 15 minutes (minues the re-do because I had the magnets wrong; see Tip).

1. Take off the strings by any method you want (I just loostened them and removed the tailpiece from the bolts). Remove the cover screws on the bridge pickup (doesn't matter which, but the bridge seemed to have a bit more wire slack. If not, open up the vol/tone cover and carefully snip a cable tie to free up the cables)
2. Carefully lift the pickup out of the hole. It should be waxed together, so nothing should fall out. Take a Sharpie and mark the outside edge of the two magents above the bottom plate. Also mark the top of the bobbin. This is very important as magnet polarity is key.
3. Unsrew the pole pieces (six screws on top) and the two screws holding the bottom plate to the pole plate (thin metal strip that sits between the magnets). Carefully take out the magnets. Since everything is waxed together, gently pry apart with a small screwdriver.
4. Flip the bobbin over and arrange the plate and pole plate between the bobbin bottom (used to be the top) and the plate. Put the magnets back in between the bobbin and the bottom plate, making sure that the edge that you marked is now on the inside against the pole plate. If you have a compass handy, make sure that the pickups now have different magentic polarity (one should attract N, the other S as you hold the compass perpendicular to the pup face).
5. Re-attach all the screws and re-install the pup and cover. Congratulations, you now have humbucking P-90 axe when playing in the center position.

Tip: If the center position is hum-free, but sounds thin and nasaly, the magnets are not installed correctly.

Why does this work? Because the 60 Hz hum only interacts with the coils, so reversing one causes a phase inversion that cancels out the hum. The strings interact with the entire coil/magnet system, so reversing the magnets reverses the phase once again, resulting in a zero phase reversal, just like the original. Neat huh?

#2 User is offline   Darren W 

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Posted 30 September 2010 - 03:15 PM

Brickster good mod, and well thought out, but isnt that taking out the heart and soul of a P90, it just wouldnt be the noisy beast that they're meant to be.
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#3 User is offline   Brickster86 

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Posted 30 September 2010 - 05:44 PM

View PostDarren W, on 30 September 2010 - 03:15 PM, said:

Brickster good mod, and well thought out, but isnt that taking out the heart and soul of a P90, it just wouldnt be the noisy beast that they're meant to be.


The hum cancelling is only in the center position; it actually still sounds really good. Remember you still have 2 "pure" P-90 modes by selecting the rhythm or treble positions. I think this is a better alternative than replacing the P-90s with humbucking replacements. If you can't stand the quiet, you can always change it back! :)

#4 User is offline   kevin134 

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Posted 30 September 2010 - 05:57 PM

I had a Reverend Roundhouse and have two reverends(Slingshot and a Jetstream that are hum cancelling in the center postion. The Jetstream is a 390, so center pup is RW/RP, not sure how they made them hum cancelling on the other two. I wish I had known your mod when I had my Epi Les Paul Special DC with p90's, that thing hummed horribly(I think the pups were actually p100's, didn't keep it long enough to find out though). I know after market pickups are available RWRP for people that are planning pup changes..
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#5 User is offline   animalfarm 

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Posted 30 September 2010 - 10:20 PM

P-90 USERS, please "weigh in"/comment on this technique. I've
always used either Single coils (Strat) or Humbuckers, NO experience
with P-90s.

Always notice whenever little tips and tricks show up - possible
inclusion in Epi Lounge "DIY" Sticky/Thread? I'll do some research for similar
solutions now that I've read HOW Brickster86 did it. Gives me more defined
search terms.

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#6 User is offline   Notes_Norton 

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Posted 01 October 2010 - 07:07 AM

I put GFS Mean 90s on my ESP-FauxLP and one of the pups is RPRW. This doesn't take the heart and soul out of the P90 sound at all, unless I choose both pickups.

What it does is gives me some versatility. With either pup chosen, I get that beautiful P90 sound. Put the switch in the middle position, and I get what is essentially a huge humbucker and it does have humbucker characteristics.

What I would really like to see is a guitar with a "balance" potentiometer instead of a switch. That would give me a lot more choices than bridge, neck or both but I could have mostly bridge with a little neck or any other variation. It would have to be wired so that in either extreme position it would select only one pickup.

I don't know of any guitar that does this, or any mod for that.

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#7 User is offline   animalfarm 

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Posted 02 October 2010 - 12:52 AM

Brickster - any similarities between what you did and the following
link? Link is in the "Do-it-yourself" Thread in the Epi Lounge, under
"Guitar Pickup Info":

(Has Pics)

"How to change out a Humbucking Bar Magnet"
http://www.projectgu.../barmagswap.htm

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2010 Ovation CC-24 Flamed Koa Top Acoustic-Electric
2010 Jay Turser JT-200 Pro Les Paul Double Cut-Away (TransAmber), Gibson Deluxe Tulip Tuners
AMPS:
Crate (mid-90s) Vintage Club 50, all tube 50W
Vox VT-15 Modelling Amp, 15W
Marshall MG15CD Amp, 15W

#8 User is offline   Brickster86 

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Posted 02 October 2010 - 03:32 AM

The other mod is quite messy! The mod I did is way more straightforward (step 2 is the same what I did). The only similarity is the removal of the magnets, but not replacing per se. Fortunately, the P-90 covers just come right off and the only tool required is a Phillips screwdriver and perhaps a small blade screwdriver to pry out the magnets.

#9 User is offline   bigneil 

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Posted 02 October 2010 - 03:34 AM

View PostNotes_Norton, on 01 October 2010 - 07:07 AM, said:

I put GFS Mean 90s on my ESP-FauxLP and one of the pups is RPRW. This doesn't take the heart and soul out of the P90 sound at all, unless I choose both pickups.

What it does is gives me some versatility. With either pup chosen, I get that beautiful P90 sound. Put the switch in the middle position, and I get what is essentially a huge humbucker and it does have humbucker characteristics.

What I would really like to see is a guitar with a "balance" potentiometer instead of a switch. That would give me a lot more choices than bridge, neck or both but I could have mostly bridge with a little neck or any other variation. It would have to be wired so that in either extreme position it would select only one pickup.

I don't know of any guitar that does this, or any mod for that.

Notes

could still have 3 way toggle but use a pot of some sort as a blender for the middle position, or if there is a volume for each pick up then you have two pots as a blender anyway.
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#10 User is offline   KX36 

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Posted 02 October 2010 - 05:01 AM

It seems to be a pretty good mod. There have been mods before to reverse the magnet the same way but many change the wiring to reverse the winding which can cause problems if there's a safety ground and a signal ground on the same wire. Of course a lot of people just buy reverse wound reverse polarity P90s.

Basically boils down to open the pickup, take out the bobbin and flip it over so that the top becomes the bottom and bottom becomes the top (just clarifying incase people "flip" it by rotating it 180 degrees which wouldn't make a difference), rotate the magnet 180 degrees so N becomes S and S becomes N; now it is reverse wound reverse polarity without having to change any wires and any baseplate ground is still on the ground wire, unlike some other mods that reverse polarity by reversing wires which accidentally puts that ground onto the hot wire And it will cancel hum in the centre position but act as a normal P90 in the bridge or neck position.

Is the P90 one of the pickups where the polepieces are directly touching the coil wire or not, and is it the same for all manufacturers. It's a bad idea to remove polepieces completely if they touch the wire because there's a good chance of breaking the wire when you put them back in; but if they're not directly touching, should be a good mod.
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#11 User is offline   Notes_Norton 

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Posted 02 October 2010 - 07:38 AM

View Postbigneil, on 02 October 2010 - 03:34 AM, said:

could still have 3 way toggle but use a pot of some sort as a blender for the middle position, or if there is a volume for each pick up then you have two pots as a blender anyway.

I've decided that two vol and two tone knobs have the advantage of giving you more tonal options, but the disadvantage of changing them quickly on stage.

I modded my LTD-fauxLP so it has one vol and one tone knob, and I find I use them a lot more than I do on either my Gibson or my Epiphone. It's quick and easy and can be fine tuned while playing - much easier for me anyway.

A balance knob in addition to the pup switch would be a nice touch, although not necessary.

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#12 User is offline   cjlandry 

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Posted 02 October 2010 - 08:38 PM

Probably not helpful in this thread, but the Seymour Duncan Phat Cats behave this way on my SG. Middle position is like a humbucking position. They're set up for this, if you get a matched pair.

Also, I just bought my daughter a Squier mini-strat, and I notice that when it's switched to neck/middle, or bridge/middle, the hum goes away, although it's there in the other positions.

The "humbucker" theory works, even with single coil pickups, if they're arranged properly.


Cool mod, BTW!
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#13 User is offline   animalfarm 

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Posted 04 October 2010 - 12:08 AM

Brickster, for some ODD reason, I'm having a heck of a time
wrapping my brain around exactly what was done - "flip the Bobbin"?
I read a Bobbin can be made of plastic, wood, etc. Flipping it would
seem to be of no difference. Flipping a Magnet, yes.

I AM both Mechanically AND electrically inclined, but reading the
TEXT description you provided leaves many questions unanswered for me.
Why?
I'm an Idiot.

To this end, I'm inserting a PIC of a P-90 expanded. Can anyone help
this poor, brain-dead git player understand better? Use pic if helpful.

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GITS:
2006 Epi LP Classic (Amber Quilt Top), 498T/490R Gibson pups, Gibson Deluxe Tulip Tuners
2010 SX Hawk Strat Copy w/ two P-90s, Mahogany with Maple neck/Fretboard, with Stop-Tail
2010 Ovation CC-24 Flamed Koa Top Acoustic-Electric
2010 Jay Turser JT-200 Pro Les Paul Double Cut-Away (TransAmber), Gibson Deluxe Tulip Tuners
AMPS:
Crate (mid-90s) Vintage Club 50, all tube 50W
Vox VT-15 Modelling Amp, 15W
Marshall MG15CD Amp, 15W

#14 User is offline   Brickster86 

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Posted 04 October 2010 - 02:00 PM

Thanks to animalfarm for the great exploded P-90 picture. I edited this and added a few tips on rotation/flipping of the parts that I describe. Hopefully this makes it more clear. Basically, you rotate the bobbin so that the top is now the bottom, and vice versa (axis of rotation is the around where the cable comes in on a short side.) Think of just grabbing the cable, and turning the bobbin upside down.

Each magnet gets rotated like a propeller so that the poles are swapped (note that the poles are on the long sides, not the short sides like you would think). Don't flip them, just make the inside now the outside, and vice versa.

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  • Attached Image: P-90.jpg


#15 User is offline   Brickster86 

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Posted 04 October 2010 - 02:14 PM

View Postanimalfarm, on 04 October 2010 - 12:08 AM, said:

Brickster, for some ODD reason, I'm having a heck of a time
wrapping my brain around exactly what was done - "flip the Bobbin"?
I read a Bobbin can be made of plastic, wood, etc. Flipping it would
seem to be of no difference. Flipping a Magnet, yes.

I AM both Mechanically AND electrically inclined, but reading the
TEXT description you provided leaves many questions unanswered for me.
Why?
I'm an Idiot.

To this end, I'm inserting a PIC of a P-90 expanded. Can anyone help
this poor, brain-dead git player understand better? Use pic if helpful.

Posted Image


flipping the bobbin changes the winding direction of the coil. The induced signal current from the 60 Hz source is now 180 degrees out of phase with the signal current from the other pickup, therefore canceling out the 60 Hz noise. Flipping the magnets is required to get the string signal back in phase with the other pickup.

#16 User is offline   animalfarm 

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Posted 04 October 2010 - 02:21 PM

Thank You! Me Unner-Stand, now! My disadvantage was not
having a P-90 pup in hand to look at regarding electical connections.

Posted Image

You have done what is similar to a "Peter Green" Mod
when done to HumBuckers - involves reversing polarity of Magnet.
Hmmmmmm.... need to do a thread on that! There are MANY, MANY
search results on this.

Peter Green Mod (in a nutshell):
http://www.sweetwate...s/d--10/03/2007

GITS:
2006 Epi LP Classic (Amber Quilt Top), 498T/490R Gibson pups, Gibson Deluxe Tulip Tuners
2010 SX Hawk Strat Copy w/ two P-90s, Mahogany with Maple neck/Fretboard, with Stop-Tail
2010 Ovation CC-24 Flamed Koa Top Acoustic-Electric
2010 Jay Turser JT-200 Pro Les Paul Double Cut-Away (TransAmber), Gibson Deluxe Tulip Tuners
AMPS:
Crate (mid-90s) Vintage Club 50, all tube 50W
Vox VT-15 Modelling Amp, 15W
Marshall MG15CD Amp, 15W

#17 User is offline   Whitmore Willy 

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Posted 05 October 2010 - 07:34 AM

Gentlemen, and the rest of you (kidding)

My apologies as this is slightly off subject.
As the discussion concerns P-90s I have a question. Does anyone know the difference between Gibson soapbar P-90 pickups and Gibson "Super Vintage" soapbar P-90 pickups?
Couldn't see starting another thread while those participating in this one seem very knowledgeable on the subject of P-90s.

Willy

#18 User is offline   gaz0 

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Posted 03 December 2010 - 09:04 PM

Sorry guys, this is nothing but the Peter Green mod done on a P-90. Assuming you started with both pickups In-Phase and Not-hum-canceling, this will not give you hum-cancelation. All it will do is make the pickup Out-Of-Phase while still being Not-Hum-canceling. You can never have hum-cancelation between two coils if they are the same current flow/wind.

You need to have either both factors Magnet Polarity and Current Flow (wind) to be the same, or both be opposite for the two pickups to sound In-Phase when combined. If you look at this chart, you'll see what I mean what happens if you only change one of the two factors. (You started in a blue box, and swapping one pickup's magnet moves it to an orange box). Magnet Polarity and Current Flow (wind) are two independent factors. Changing one does not change the other and vice versa.

You will need to desolder the hot and ground leads from the braided shield at the base of the pickup, then separate the ground lead from then shield, then swap the hot and ground leads where they exit the pickup, the solder the braided shield back to the ground lead at that point. Sorry there is no way around this. If you swap the hot and ground without separating the shield wire, it will introduce noise into the signal path. Likewise if you soldered the braided as your hot wire at the volume pot or switch. I speak from 12 years pro guitar electronic experience. One of my earliest mods was swapping magnets and leads on an Antiquity P-90 neck to get hum-canceling with the bridge.

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#19 User is offline   RaSTuS 

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Posted 04 December 2010 - 02:31 AM

Welcome to the forum gaz0, and thanks for your post. I'm considering a P90 install soon and I'm just lapping up this stuff.
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#20 User is offline   AS90 

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Posted 04 December 2010 - 11:18 AM

My Tele is hum cancelling in the middle too...

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