OT: Dummy coil - has anyone done this and does it work?

[aron]

and HOW does it work?


Basically pop out the magnets, remove the wire connecting the switch to the volume pot (the main signal wire) and replace with the pickup wires (one to the switch and other other to the volume pot).


How does this reduce hum?


https://www.youtube.com/watch?v=Vj2RloyhxMY

[aron]

ahhh I think, as I suspected it doesn't work. Check out the comments from the youtube link below:
https://www.youtube.com/watch?v=EmX_5tlPFUo

[Puguglybonehead]

OK, the guy in these videos seems completely clueless. A dummy coil only works if it is reverse-wound to the other pickups. If say, all 3 pickups on the strat are wound clockwise, then you need a dummy coil that is wound counter-clockwise. That is how you get hum-cancelling.  There is no mention of that in this guy's videos. So, you need to know which way your pickups are wound in the first place. To make matters worse, many of the modern strat-type guitars come with a reverse-wound middle pickup. (so you get hum-cancelling in the bridge/middle combo or the neck/middle combo) The second guitar I built in the mid-1980s got this wiring setup. So now, wiring a dummy coil gets more complicated. (the solution should be obvious though) It also helps to have a dummy-coil that is wound to roughly the same value (say 6.5k for a strat) as the other pickups. I also noticed that this guy didn't seem to bother to re-attach the ground wire to his bridge. (and strings) Hum problems abound there.

[tommycataus]

Ah brilliant. So simplistically it works the same way as a humbucker in that you have two magnets with roughly the same number of coils wound in opposite directions, but the dummy coil is not used as a pickup. Pretty clever.

[Mustachio]

I coulda swore I remembered good 'ol Mark Hammer talking about this before on this forum , turns out it wasn't only him it was another smart forum member Drolo who started the thread. It's a good read.

http://www.diystompboxes.com/smfforum/index.php?topic=104834.msg941897#msg941897

[tommycataus]

That is brilliant. Thanks for that Mustachio! So I was incorrect... It doesn't need a magnet at all. Will try this in one of my strats for sure. Added to the ever growing list of stuff I want to build   

[anotherjim]

If the reverse coil is expected to also produce useful signal from the strings, don't forget the magnet polarity must also be reversed otherwise it will cancel signal as well as hum. An independent noise cancelling winding placed outside the string run wouldn't work perfectly. It wouldn't be in the same plain as the working pickup (so could have a different noise signal) and could only ever match a single working pickup for noise level.

[Rob Strand]

Pulling out the pole pieces on the "dummy" coil is also a bad idea.  The presence of the pole pieces change/increases the sensitivity of the dummy coil.   That's why humbuckers have pole pieces.  You could tweak the number of turns on the dummy coil to compensate.  The dummy coil doesn't need any magnets to work.

One thing though shielding and grounding of the dummy coil should not be ignored.

[ashcat_lt]

If its expected to make string sound then it's not a dummy coil, it's a pickup.    A dummy coil that is nowhere near the strings could have a magnet.  Wouldn't make much difference, except it would risk microphonics and might amplify your belt buckle or something.  Damn it's early!  :/

Anywho, we've had a thread over at GN2 for a while Dummy Coil Experiment - Successful

[ashcat_lt]

Pulling out the pole pieces on the "dummy" coil is also a bad idea.  The presence of the pole pieces change/increases the sensitivity of the dummy coil.   That's why humbuckers have pole pieces.  You could tweak the number of turns on the dummy coil to compensate.  The dummy coil doesn't need any magnets to work.

One thing though shielding and grounding of the dummy coil should not be ignored.

You ninja'd me!

You wouldn't want to shield the dummy coil any better than the pickup it's supposed to be humcancelling with, or you'd be defeating the point.  A full shielding job kind of is a big dummy coil.

It'll be wired into the circuit exactly like a pickup, and you do in fact get the choice to put it in series or parallel with your other pickups and it will have the same effect on tone as if it was another pickup except that it won't add any harmonic content.  That is, it will act like a big inductor either parallel or series with the acting pickup.

[Rob Strand]

shield the dummy coil any better than the pickup it's supposed to be humcancelling with, or you'd be defeating the point.

Humm pickup is usually magnetic where as buzz in usually capacitively-coupled.   There are two different effects, both bad.   Electrostatic shielding doesn't help low frequency magnetic interference (eg. a magnetic field will pass through an aluminum sheet).

If you can match the dummy coil to the other pickups you should be able to get some hum cancelling.   If all pickups are the same this is a lot easier.  If they pickups are different, hum cancelling coil can only match perfectly to one pickup.  In practice you would match to average sensitivity of all the pickups.  The more variation between the pickups the worse the overall hum cancelling effect.   Beyond that you have to cope with two and three pickup combinations.

At the end of the day individual hum cancelling coils matched to each pickup is best.   An alternative to the humbucker is the dummy coil system used by Alembic (IIRC).

[bool]

It is debatable whether experimenting with dummy coils will in the end yield a "better tone" vs. simply swapping pickups for the "noiseless" variants.

Cost efficiency? Yes or no?

[Mark Hammer]

Dummy coils can require a lot of "support" to achieve the silence of a true humbucker pickup, so some folks will steer clear of them.

On the other hand, I imagine a great many of us would be elated to get a 6-8db reduction in hum.  And if that can be done with a dumb dummy coil, without interfering with tone or requiring a great deal out of installation, what's so bad about that?

[Gus]

I seem to remember Suhr threads

[aron]

Yes the Suhr backplate works, but this seemed so easy if it worked.

[ashcat_lt]

Just peeking at that thread I linked, there are a couple things mentioned re: the choice of series vs parallel wiring for this thing.

In parallel, he said that it was a bit quieter and seemed to reduce the low end.  I think this is not actual high-pass or bass-cut so much as an extension of the high end combined with a broadband attenuation.  Assuming that the two coils are identical in DC R and in L, the paralleled inductance will increase the cutoff of the low-pass filter that already exists by about an octave, but the coils will also act as the top and bottom resistor in a 1:1 voltage divider, so a 50% attenuation, or 6db down.  Combine more relative treble and less overall signal and it often can sound like less bass.  This is, in fact, what we'd expect if we were combining two normal pickups in parallel, though like I said above, you'd have a blending of the harmonic content from the strings themselves which makes these more subtle difference tough to detect.  I guess maybe more like parallel wiring between the coils of an HB?

OTOH - He said that he couldn't tell a difference when he wired it in series on his bass, but when he did an A/B on an actual guitar, it dulled the SC sound and seemed a little bit quieter.  This makes plenty sense because the series inductance adds, and thus lowers the LPF cutoff just like an HB in standard series wiring.  Normally, an HB would be louder than an SC, but that's of course because the strings are pushing both coils in the same direction, so you get about a 6db boost, but in this case, one of the coils is not a generator, it's just adding resistance (and reactance) to the "top resistor" of the divider which has the parallel combination of the pots and amp/pedal for the "bottom resistor".  This will cause a bit of attenuation, but shouldn't be barely noticeable in most cases.  That loss of the top octave can make it sound a lot less loud sometimes, though.

I did not go through the thread far enough to see if they got around to this idea, but it occurred to me that if you were to partially bypass the dummy coil by putting a cap parallel to it, you might be able to tune it in such a way that you get most of the benefit of hum-cancelling (at lower frequencies anyway) without the loss of top end.  It would be a balancing act, and probably best dialed in by ear, but...

[bool]

... but this seems a loadsa trouble for a not-quite-there thing if you know what I mean.

My "recipe" is beyond simple: stuff your live axe with mini-buckers for the beater and stuff your studio axe with a ton of aluminum or copper foil and keep the original (or swap some boutique) singles.

[ashcat_lt]

... but this seems a loadsa trouble for a not-quite-there thing if you know what I mean.

My "recipe" is beyond simple: stuff your live axe with mini-buckers for the beater and stuff your studio axe with a ton of aluminum or copper foil and keep the original (or swap some boutique) singles.

Personally, I just use HBs with per-pickup S/P switching, shield the whole thing with foil, and call it good.  I don't worry about subtle little cork sniffing mojo bs.  Plug it in, turn it up.  Series or parallel?  Done. 

[tommycataus]

The more I read this the more I am thinking the same thing... Maybe shielding is the way to go.

[Mark Hammer]

One of the common misconceptions is that the dummy coil has to somehow match the actual pickup.  It doesn't.  While it is true that a humbucking pickup will have two relatively matched coils, the hum-rejection comes from the two coils sensing the same amount of hum.  The string-sensing aspect generally benefits from having the two coils be similar, but the hum-sensing is an entirely separate matter.  That's why the Suhr backplate can a) be so big in circumference, and b) consist of much fewer turns than the pickups it is being paired up with.  The trick is to have a coil that is as sensitive to EMI in the location you place it, as the pickup/s it is paired with.