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FDP Forum / Guitar Mods, Repairs, and Projects / Dummy coil: Will it work on a shielded guitar (Strat)?

ejm

usa

Apr 13th, 2017 10:36 AM   Edit   Profile   Print Topic   Search Topic

OK, time for the weird question of the day.

I have been interested with the idea of adding a dummy coil to my Strat, to reduce noise picked up from wherever.

This question is NOT about the Suhr backplate system or other similar systems.

The Strat has three SC pups, and the middle is not RWRP.

I have shielded the pickguard and the main cavity with copper tape. The jack wire is shielded, and the jack cavity is also shielded.

The dummy coil is almost always placed in the control cavity. (There's really no place else to put it.)

So here is the question: If you place the dummy coil inside of a shielded cavity, is it going to work?

If it works by picking up noise floating around, and it's in a shielded space, it's not going to pick up much, right?

So the noise you'll be left with is what is picked up by the pickups, which is what you're trying to get rid of.

What am I missing?
Thanks in advance.


hotblooze

World Traveler

Wood, magnetic coil and strings.
Apr 13th, 2017 11:59 AM   Edit   Profile   Print Topic   Search Topic

There are 2 types of noises :

1. 60 cycles him.
2. Radio Frequency noises.

The dummy coil will eliminate 1 like a humbucker while the shielding will reduce 2 in a Faraday Cage situation. If the dummy coil is held down securely in the control cavity, it should not create any further noises.



M Tracy
Contributing Member
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Lafayette IN

Apr 13th, 2017 01:59 PM   Edit   Profile   Print Topic   Search Topic

I'm pretty sure you want the dummy coil in an unshielded area as close to the pickups as possible. I think you're right about the coil not picking up much noise in a shielded control cavity and therefore not canceling much noise. I'm sure someone smarter than me (Peegoo) will be around shortly with a detailed explanation or link.
Good luck and keep us posted, I'd like to try this myself.

Peegoo
Contributing Member
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The spotlight

looks like a prison break
Apr 13th, 2017 02:54 PM   Edit   Profile   Print Topic   Search Topic

I'm not any smarter than you guys. But I read a lot!

In order to be as effective as possible, a dummy coil needs to be in close proximity to the pickup(s), and it needs to be out in the same environment as the pickup so it 'sees' the same noise floor as the pickup does. It cannot be shielded.

A dummy coil cancels noise in a signal in a manner similar to a humbucking pickup or a balanced (XLR) mic cable: it creates a 'mirror image' of the signal, but 180 degrees out of phase with the pickup signal.

When the two signals are summed, any additional content that appears at the tail--that was not present in the original signal--is attenuated.

Here's a pretty good description of how this works.

Peegoo
Contributing Member
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The spotlight

looks like a prison break
Apr 13th, 2017 02:58 PM   Edit   Profile   Print Topic   Search Topic

hotblooze, there is a third noise type: airborne EMI (electromagnetic interference). This is what you hear when you move the guitar and the noise level changes with the position of the guitar.

SonicBlue

Sunbury-on-Thames

Apr 14th, 2017 04:06 AM   Edit   Profile   Print Topic   Search Topic

If the middle coil isn't RWRP, it's possible to make it so if you take a couple of brave pills.

The quick description is remove pickup, press out magnets, turn them the other way up and replace, then swap over the hot and ground wires when reinstalling the pickup.

I pressed out the magnets by supporting the fibre base with a socket which just cleared the magnet, so there's as little base as possible to flex. I used a wooden dowel to actually push them out, applying a firm and steady pressure. Replacing them is easier, they just push back in. You can fix them in place with a blob of molten wax on the base. You can even play with the stagger heights, lowering the G if you use a plain string rather than the wound variety, for which I believe the polepiece heights were originally set.

It sounds scary but it actually works. Practice on a spare or dead pickup first, if you have one lying around.


Your mileage may vary, batteries not included, actual colour may differ from illustration etc. etc.

(This message was last edited by SonicBlue at 06:09 AM, Apr 14th, 2017)

DrKev
Contributing Member
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Paris, France

It's just a guitar, not rocket science.
Apr 14th, 2017 05:55 AM   Edit   Profile   Print Topic   Search Topic

To follow up on what Peegoo said, an ideal dummy coil should also be close in size, shape, orientation, and resistance to the actual pickups, or you will never achieve the kind of hum cancelling you get from RWRP or humbuckers. And that's just about impossible to accommodate a full size coil without routing on most solid body electrics! So it's important to have realistic expectations.

A question in my mind is that the dummy will also load down the other pickups and you will have some tonal changes. One way to fix it is to build in a buffer preamp of some sort, which allows you to use any size/shape dummy coil and dial in the just the right amount of hum cancelling, which of course is what the commercial systems do. Depending on who's review of what system you read, they do a good job at low frequency 50/60 Hz hum but are not perfect at high frequency buzzing.

Personally, I have no interest in building my own hum cancelling system, even as a hobby project. I already have the Music Man Silent Circuit on my Silhouette Special and useful as it is, I'd rather just use noiseless pickups.

(This message was last edited by DrKev at 07:57 AM, Apr 14th, 2017)

ejm

usa

Apr 20th, 2017 07:20 AM   Edit   Profile   Print Topic   Search Topic

I have been talking with tech support of a manufacturer about this, getting their take on it. I think that they may not have understood the situation so far. When I get the feeling that they "get it", and give an answer that seems thought through, I'll reply back here.

Dr Kev: As far as loading goes, I'd think that it would depend on if you connected the dummy coil in parallel or series. If it's in series I'd think that the effect would be minimal.


jay1vinton

Hawaii, USA

Perfect is the enemy of good enough
Apr 21st, 2017 05:47 PM   Edit   Profile   Print Topic   Search Topic

I have a Kramer Classic Strat clone that has the dummy coil. It is placed horizontally in the bottom bout in a special rout right below the neck pickup.

It is not shielded in any way that I can see and it cancels well. I don't know if shielding would alter the effect. It still has 60 cycle, but very very little of it.

ejm

usa

May 3rd, 2017 08:17 AM   Edit   Profile   Print Topic   Search Topic

I have been corresponding with tech support at a company about this.

I think that he doesn't really understand my question (after rewording it about three times).
Or, he doesn't want to understand the question.
Or, I don't understand something. (Nah, that's crazy talk.)

The answers from him so far don't make sense to me, for any of the above reasons.
I may post them at a later date.

But, think of it this way.......

Take a regular dual coil humbucker.
Slightly separate the two coils, leaving them connected electrically.
Unless you radically alter the relative positions or something else, it would still cancel noise to some degree, right?

OK, assuming that is correct, envision this.

Take one of the coils and completely encase it in shielding tape.
Ground that shield.
Will it still cancel noise now?
I say it will not, because the shielding will keep that one coil from picking up anything and feeding it to the other coil.

So imagine if that shielded coil, instead of being shielded in its own shielding tape "blanket", were "naked" but inside of a shielded box (like a Strat pickup cavity).

What am I missing?


Peegoo
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May 3rd, 2017 02:51 PM   Edit   Profile   Print Topic   Search Topic

Yes, even with the coils separated, there will be some noise cancellation.

Consider a Tele with the four-way switch mod that adds a selection for both pickups in series (vice the standard parallel scheme). That does substantially quiet things down in an electrically 'dirty' environment.

To work properly, a dummy coil needs to be exposed to the same noise floor as the pickup it's in series with. Shielding a dummy coil reduces its effectiveness.

A dummy coil works in a manner similar to how an XLR or TRS cable cancels noise.

Two sine waves (both containing signal and noise) are overlayed upon one another, and the phase cancellation--in an ideal world--cancels all signal content in the circuit that didn't originate from the vibrating string. Humbucking operation is almost the same thing.

ejm

usa

May 3rd, 2017 08:42 PM   Edit   Profile   Print Topic   Search Topic

Peegoo: Thanks for the response. I think that you confirmed my suspicions and/or we are on the same page. However, with all due respect, you didn't answer the question directly.

So the question was/is:
Take one of the coils of the humbucker and completely encase it in shielding tape.
Ground that shield.
Will it still cancel noise now?
I say it will not, because the shielding will keep that one coil from picking up anything and feeding it to the other coil.

I'll need to go back and review my correspondence with the tech, but if I remember correctly, he claims it will still cancel noise. Which leads to my suspicions about him not really reading the questions, or not wanting to understand the question, or me missing something. Which means that if I'm missing something here, then you are as well (which I doubt).

He mentioned that Fender and Suhr (their back plate system) and recently Music Man have all did the dummy coil thing at one time or another. However, he also did not elaborate on if those guitars also had cavity shielding of some sort (tape, paint, etc.). I suspect that they do not. In the case of the Suhr back plate system, it may not matter because the back plate is outside of the cavity.

(This message was last edited by ejm at 10:46 PM, May 3rd, 2017)

Peegoo
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The spotlight

looks like a prison break
May 4th, 2017 03:55 AM   Edit   Profile   Print Topic   Search Topic

It will still cancel noise...but only noise from the AC mains. It won't cancel induced RF or other interference that wasn't introduced via the amp's end of the circuit.

There are several sources of noise, and each has to be mitigated a certain way to be as effective as possible.

DrKev
Contributing Member
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Paris, France

It's just a guitar, not rocket science.
May 4th, 2017 02:06 PM   Edit   Profile   Print Topic   Search Topic

I can confirm that Music Man do have cavity sheilding (painted, it's actually under the color coat) and foil shielding on the pickguards. Their dummy coil is a short cylinder with integrated electronics mounted on the pickguard right next to the volume control.

Steve Dallman
Contributing Member
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Merrill, Wisconsin

Age is just a number...mine is big
May 6th, 2017 05:40 PM   Edit   Profile   Print Topic   Search Topic

A typical humbucker with a cover is completely shielded but it works.

I built a bass years ago with a Dimarzio J pickup. I later used the humbucking, side by side coil Dimarzio with an EMG Select.

The EMG Select was a single coil. As with a Jazz bass, when both pickup are turned up, or set the same, the pair is humbucking.

I put the other EMG Select in the shielded control cavity and wired it with the neck pickup. I had a series/parallel switch on the bass for the former Dimarzio. I wired that switch to the pair.

It worked great. No noise. The two sound with the switch worked well, and the pickup mixed well with the EMG Select P pickup I used...modded to also have a series/select pick.

FDP Forum / Guitar Mods, Repairs, and Projects / Dummy coil: Will it work on a shielded guitar (Strat)?




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