Dummy Coil: Question from a dummy.... ANSWERED!!!

[BigSteve22]

My house has got to be one of the most "electrically noisy" places on the planet. Between early 80's cheap housing boom wiring, three TVs, (including a large plasma), old appliances, four computers, a wireless and hard wired Ethernet, and a bagillion DC warts, I'm surprised anything works at all. I can't even play my son's Squire strat through an amp, it's that bad! HBs and "noiseless" pups are OK, as are single coils played in combo with an RW/RP counterpart. But lone single coils absolutely screams for help.

My Jazzmaster has SD P-Rails. In parallel or series HB mode, or with both P-90s or Rails active, it's all good. But try just one pup, in either single coil mode, and EMI hell fills the air! If I stand or sit at just the right angle, face the neck into the wall, and don't move, I does abate quite a bit, but I like to sit back on my couch, which is not one of positions the EMI gods allow!

Looking for a solution, I found various reference to the use of dummy coils. Some articles/videos put them in series with the signal path, and some ran them in parallel. All claimed to provide relief, but I remain skeptical. An option I'm considering trying, is to mount a pickup coil, (magnets removed), under the pickguard, (in already available, empty space), close to the pickups, and wire it in parallel to the output with both an on/off and a winding reversal switch, therefore allowing the coil to be add to the circuit only when needed, and provide a means of reversing the winding depending on the pup it is paired with.

Switches are already in place. My original wiring included two CTS DPDT-Push/Pull pots which I used to modify the tone circuit so I could change not only the Cap value, but the Pot value as well. This is the original schematic:

It was a novel idea, and I had great expectations about being able to vary the tone circuit configuration to match the various modes of the P-Rails. However in practice, the differences were barely noticeable, if at all. For this reason, I was already considering simplifying things under the hood. Playing with things today, I came up with the following idea:

The coil, L1, is a cheap 5.9K strat pup with no magnets. The cross wiring in switch S2 allows for reversing the windings, while S1 either connects it, or grounds both ends of the coil, totally removing it from the circuit. A simple tone pot with a single cap, and a volume control with a treble bleed complete the control package.

If you've gotten this far, you're probably an engineer, and that's exactly who I'm hoping to get some guidance from! These are my questions: Does this sound reasonable? Am I going about this the right way, or am I missing something obvious? Is wiring it in parallel the way to go, or should it be in series? I'm certainly not an engineer, and any input would be greatly appreciated.

My intention is to try clipping the coil in place and see how it goes before committing, and I also intend to tighten up the wire shielding. I'll be going at anyway, just wanting to know if I'm on the right path or about to step off a cliff! Thanks in advance.

 

[stratamania]

An interesting plan and dummy coils are the basis of systems such as those of Illitch albeit they are disguised in pickguards or backplates. The only way you are going to know for sure is to experiment with it to see what results you get with a DIY solution.

I am a little concerned and don't know about US wiring regulations from the 80s to now but feel I had better suggest a slightly bigger and more expensive job might be considering bringing your house wiring up to date.

 

[Cagey]

A "dummy" coil all by itself, wired in series or parallel but out of phase with the pickup, will reduce a great deal of noise pickup via CMNR (jpg). Unfortunately, it will also reject a great deal of desirable signal as well, which is why you don't generally see it in guitars/basses. It's been tried, with varying degrees of success, but even in the best of cases the downsides have been too much to bear. Typically, you end up with something that sounds entirely too weak/thin to be useful, even for ultra-twangy hillbilly music. John Suhr has a system that puts a much larger coil on the back of the guitar that works fairly well, but it still has a somewhat detrimental effect on the inherent sound quality of the pickups you're trying to clean up, so it hasn't gained much acceptance in the market.

The concept can be made to work if the second coil is part of the pickup with an opposite polarity magnetic field induced in the pole pieces, and that's the basis of "humbucking" (noiseless) pickups.

There are other tricks, but they're not easily implemented on the kitchen table at low/no cost. Fortunately, they can be had at (usually) reasonable cost.

Bill Lawrence's "Microcoil" pickups are remarkably quiet without the use of tone-robbing dummy coils, and they're very reasonably priced. They also sound like single coils should. Highly recommended, but lead times can be long.

GFS makes the both the Neovin and Tru-coil lines of pickups that, while using dummy coils, still sound very much like single coils. Also priced quite low. The True-coils sound more authentic, but they're not completely noiseless. They're "noise-reduced". There's no official number on it, but I'd put it at about 80%. The Neovins are noiseless, but slightly compromised tonally. Still, closer to authentic than many of the other offerings out there.

Finally, in the pickup solution category, there's the new Fishman "Fluence" offering. Sound fantastic, produce no noise, but require onboard power and a healthy pickup budget.

If you don't want to modify the guitar, you can always just do the noise gate thing. Technology has improved on those things dramatically to where they're not as intrusive as they were years ago. But, even with better units, if your noise level is high, the gating threshold on the device has to be set high, and you'll hear the gate abruptly opening/closing even with all the filtering/smoothing some of them can do. Although, I've heard good things about EHX's "Hum Debugger". Apparently, it's more of a narrow-tuned filter designed to specifically attack 60hz than a gate, so you don't hear the gating action so much.

I've actually used everything mentioned above except the Hum Debugger, just so you know I'm not repeating press releases  :laughing7:

Incidentally, unless your house is very old and doesn't have ground lines running anywhere, it's highly unlikely that's causing you any heartache. It's the loads on the lines that'll do it. Any inductive loads like motors, ballasts or large transformers will radiate like crazy. The wavelength of 60hz is quite long, so you need something like a mile of wire and a lotta power to transmit it, and the same length (but no power) to pick it up. Transformers and pickups satisfy both of those requirements.

 

[stratamania]

The system Suhr used to use was or was similar to the Illitch system I mentioned before. Now Suhr, use a proprietary system inside the body, not a backplate.

As for market acceptance, you are unable to buy the Suhr system unless it is on a Suhr, most of the Classic Pros etc come with it stock. Seems to be well received and works well.

The Illitch system you can buy.

 

[drewfx]

The problem with dummy coils is they add to the impedance of the PU and thus can mess up the tone.

The solution to this is to have active buffering circuits to isolate the PU from the dummy coil. That's what the Alembics of the world do, but for whatever reason many guitarists have an unnatural fear of active circuits built into the guitar as opposed to active circuits in a pedal or amp or anywhere else.

 

[BigSteve22]

Thanks for the replies. I'm still looking at a few things, I'll let you know when I have a chance to actually get on with the experimenting. Any suggestions regarding a buffering circuit that can be installed inside the guitar? Buy or build, as long as it works! Love the P-Rails, just want to kill the noise. Thanks again....

PS: As for the house wiring, it's up to spec, but it's all done with Romex cable, so it has an dedicated internal bare copper ground, but lacks the external shielding of a BX installation.

 

[BigSteve22]

Update
Today I built up a little test rig, just a short length of cable, a couple of Amphenol plugs, with a pair of leads attached to one end plug, terminated with alligator clips. I used this to  test the effects of running a dummy coil in parallel with the signal path. (Note that I understand that the unshielded leads will add to the EMI noise, but just wanted to see what would happen.)

I clipped the coil in both directions and on both the P-90 and Rail coils. The coil definitely reduced the buzz, and polarity appeared to be of little effect, but it also definitely cut not only the overall signal strength, but also clipped the crap out of the treble end! (As predicted by my friends here.) So, scrap that idea! Moving on...

Looking around the web, I came across a video of a guy who uses a dummy coil in series with the signal. He removes the magnet and the pole pieces and then shields the coil. His thing is that the coil increases the impedance without introducing any noise.
[youtube]https://www.youtube.com/watch?v=8pqzTkJhRRY[/youtube]
(In a second video he gives a very brief demo, which appears to have achieved the desired effect, but spends most of his time missing the point about coil winding direction, comparing it switching  which end of a straight cable is plugged into his amp....) Oh well, the guy who first suggested I drink beer was no genius either, but he certainly turned out to be right! I'll try this when I get under the pickguard.

Also, while looking around, I came across this circuit from a UK web site, Stompville: http://stompville.co.uk/?p=1174

The author explains, in simple terms, about the differences between source and load impedance, and advocates for the use of an active buffer, although not specifically in regard to 60Hz noise reduction. Anyone tried something like this INSIDE a guitar? (Minus the jacks, of course.) Any thoughts as to whether this might work to reduce the 60Hz buzz?  :icon_scratch:

 

[Cagey]

Buffers are not for reducing noise, per se. You could think of them as a "reservoir". When loads draw more current from their source, the source's voltage may drop, resulting in less signal being available for the load to use. A buffer allows more current to be sourced, so the voltage doesn't drop.

Guitar pickup outputs are pretty small, so feeding some sfx pedals can load the signal to the point where the output from the sfx suffers, or the following device(s) suffer. So, you buffer it.

 

[BigSteve22]

That makes sense. The schematic looks sorta like a single stage amplifier if you replace the jfet with a PNP. Add a voltage divider at the base and caps the prevent he flow of DC. (?)

Anyway, you say it's "not for reducing noise, per se", but would it have that effect? I mean, what's the process behind active pickups being "noiseless"?  ???

 

[Cagey]

No, it won't reduce noise. Ideally, it shouldn't affect the signal at all, it should just provide some oomph behind it in case it sees more load than the guitar pickup could source easily. No gain to it.

Active pickup electronics actually are a bit of a gain stage. The pickup itself is pretty weak and has a lot less windings to the coil, so it never picks up as much noise as the standard high-impedance parts we typically use. In other words, you've got a much shorter antenna. So, you're not noise-rejecting so much as never having much noise to reject.

I think that's a little bit of how the Bill Lawrence Microcoils work. If you look at a picture of one, you'll see the coil is actually pretty small.

They use a much finer wire to wind it, so you end up with the higher impedance the amp needs to see in order to match up. End result is very low noise, and no dummy coil or preamp needed, but still sounds like a single coil because that's what it is.

 

[BigSteve22]

.....you've got a much shorter antenna. So, you're not noise-rejecting so much as never having much noise to reject.

Gotcha. And thanks for your explanation of the Micro Coil design. I love the Wild Bill noiseless pups in my Tele. They're not the Micro Coils, but they do sound wonderful, and hell, certainly can't complain about the price!

Any thoughts on the shielded, series wired, dummy coil?

 

[Cagey]

Won't work. First, the dummy coil is there to pick up the same noise as the signal coil, but since it's connected out of phase, the noise it picks up is the exact opposite polarity of what the signal coil is picking up, so when added together, the net result is 0. You've "bucked" the hum; so far so good. But, you also end up filtering some of the signal that you want out of the first coil by running it through the second coil, which doesn't have the opposite signal in it, but still has an impedance to it that will restrict current flow below some frequency. So, you've now changed the character or tone of the pickup. Then, if you were to shield that dummy coil, it wouldn't pick up any noise, so there'd be nothing to do any cancelling with, so you'd be left with a noisy modified-tone pickup. Going backwards here.

 

[BigSteve22]

Won't work. First, the dummy coil is there to pick up the same noise as the signal coil.......

That's kinda what I thought. May have to spring for one of these:
https://www.ehx.com/products/hum-debugger
Looks good, good company too. Anyone with experience with one of these?

 

[Cagey]

I don't personally have any experience with them, but someone I trust who also belongs to the He-Man Noise Hater's Club had nothing but wonderful things to say about the thing. Judging by the way it works, it seems like what they've done is rather than gate the signal according to a threshold setting, it's a very narrow band (like, 3rd order Butterworth) filter that just bites out a chunk between say 57hz and 62hz, so 60hz noise can't get through, while everything below and above does. You lose a tiny bit of low end, but it's such a narrow bit that you don't notice it. It's down in the weeds where the drums/bass players live anyway. Keeps you from hearing the gating effect some units have, particularly with high-noise pickups like single coils where you would typically need to set a pretty high threshold on the gate.

If that's in fact how it works, the downside would be that it would less effective on harmonic noise, such as you might get out of ballasts and flyback transformers, so things like florescent/neon lights and TVs/computer monitors would still show up in the signal. But, without the muscle of the 60hz carrier to ride on, you may not hear them as much anyway. If you do, because the environment is so overloaded with interference, then a gate could be added to the chain to remove that last little bit and you wouldn't notice it working because the threshold could be set much lower. Everything would just be silent unless you're actually playing.

 

[Sovereign_13]

Sounds like it's an off-board notch filter, which I was just about to suggest (albeit on-board).  It's possible to implement something like that on-board as an IC, but any higher-order filter is going to need to be active to get a reasonably high amount of rejection in such a narrow band (I was thinking more like 8th-order Butterworth).  Easier to get batteries in and out of pedals, plus you'd need regulating circuitry...and maybe a clock...

Still doable as an on-board effect, but probably not worth the time and effort it would take to build it out.

 

[BigSteve22]

I don't personally have any experience with them, but someone I trust who also belongs to the He-Man Noise Hater's Club had nothing but wonderful things to say about the thing.

Yeah, the few reviews I've seen of the Hum-Debugger all rave about it. I have an NS-2 which will work after a fashion, but I have to crank the threshold up nearly all the way, and you still hear the noise except when you're not playing at all. I'm thinking tha EHX unit is the way to go.

Sounds like it's an off-board notch filter, which I was just about to suggest (albeit on-board).  It's possible to implement something like that on-board as an IC, but any higher-order filter is going to need to be active to get a reasonably high amount of rejection in such a narrow band (I was thinking more like 8th-order Butterworth).  Easier to get batteries in and out of pedals, plus you'd need regulating circuitry...and maybe a clock...

Still doable as an on-board effect, but probably not worth the time and effort it would take to build it out.

I'm a tweaker from WAY back! Maybe have to build something like this just for S&Gs. My oldest is actually an EE, maybe I'll brow-beat him into designing something for me. After all, Father's Day is just around the corner!  :icon_jokercolor:

 

[Sovereign_13]

I'm also an EE, though pretty early still in my career.  I'm still impressed at the level at which we can take reasonably complex filters (even active filters) and make them the size of a dime, feed them a single-end supply and maybe a few small external caps for filtering/frequency setting, and have them work as well or better than whatever cobbled-together analog RLC filter we could piece together from discrete components.

 

[BigSteve22]

Amongst other goodies that arrived today, is my new EHX Hum-Debugger pedal. All I can say is...
OMFG! This thing is phenomenal! Plugged in my JM, put it in P-90 mode, selected just the bridge pup, turned on the amp, hit the new pedal, and DEAD QUIET! Not a buzz or hum to be heard! Played for about an hour, switching the pedal on and off, and I swear the only thing that's effected is the hum. Bridge pup in both P-90 and Rail modes is bright and clear, while the neck settings sound warm without being muddy. If there is any tonal difference at all, it's so minor I really can't tell if I'm hearing it or just imagining it.

All this, and no "gating artifacts". My NS-2 kills everything when the level drops below the threshold, sort of like shutting a window facing a noisy street.  But this thing has no threshold setting, in fact, it has no settings or controls at all, except an On/Off switch and a Normal/Strong switch. There is no effect on sustain, no clamp down, no trade offs, just blissful, natural sustain as the notes decay.....

Only down side I can see, is the fact that it runs on 7.5v AC, instead of 9v DC. Not a big deal, as they include a P/S in the box, (a lot of companies don't do that lately), but it should be kept in mind when considering where to park this thing on a pedal board.

Right now my Jazzy is hanging in it's Hercules stand, set for just the bridge pup in P-90 mode, facing a 42" plasma tv, and sitting right next to my laptop, pedal board P/S, various wall warts, and my cell and portable phones. Still, no hum at all!

Thanks to all for your input and suggestions. My question has been answered, and my hum problem solved. As a charter member of the He-Man-Noise-Haters club, I highly recommend the EHX Hum-Debugger!  :icon_thumright:

 

[Cagey]

That's great! I'm glad that worked out for you!

 

[rgand]

Thanks for the tip. I'll remember that item.