question about noise sensing coils...

[John Carlsen]

Hey folks. I've been messing around with making a dual coil strat pickup, but don't really have the materials/money to pour into experimenting a lot. I've read pretty much every thread on this board about such things, but my biggest question is about wiring it up. I've seen some pickups with on bifilar core and two coils, but the magnet wire never gets separated, meaning that it's all the same piece of magnet wire, it just switches directions. Obviously there are some issues with this. I've also read all the patents and such from the various "big guns" in the industry, but they never say anything about how they are wired. So, my basic question is: can the bottom noise-sensing coil be completely disconnected from the signal chain, or even not connected to anything, and still cancel noise while allowing the top coil to be connected like a regular single coil pup? Or do the coils need to be connected together somehow?

If I did this, would I be able to make the bottom coil very small and still have it cancel hum?

Thanks guys, you're the best! Thanks to you and to Jason's book, I've been able to make some pretty killer pickups for me and my friends!

[David Schwab]

So, my basic question is: can the bottom noise-sensing coil be completely disconnected from the signal chain, or even not connected to anything, and still cancel noise while allowing the top coil to be connected like a regular single coil pup? Or do the coils need to be connected together somehow?

No, the dummy coil must be in the signal chain, because the noise is in the signal chain. The dummy coil is wired out of phase with the string sensing coil.

If I did this, would I be able to make the bottom coil very small and still have it cancel hum?

The trend with stacked Strat pickups is to have the bottom coil smaller. But there are other tricks involved.

[Mark Hammer]

Don't confuse "in the signal path" with "has to be part of a pickup or look like one". I've had some success sticking a dummy coil in the control cavity of a Tele, and John Suhr has placed the hum-sensing coil on the plastic vibrato-arm backplate on a Strat. If I'm not mistaken, a number of other efforts have located the dummy coil under the pickguard in various forms.

The coil does not HAVE to be such that it provides an audible impact on overall pickup inductance, but if hum-cancellation occurs by mixing two opposite and roughly equal hum signals, then the coil must be connected to the circuit.

Of course, if the user/maker wishes to disconnect the dummy coil from the circuit, when the hum risk is negligible, and the cost to the tone is greater than the savings in hum, that's possible too.

[John Carlsen]

I suppose i'm starting to understand all of this. If I'm wiring the two coils out of phase with each other, what does that mean exactly? Is it similar to wiring it in series? I'm a bit of a n00b in this particular aspect of things.

Also, when I tried a noiseless pickups before, it actually worked pretty well. I used a bifilar core and just had the two separate coils wound opposite each other. However, when I put it in the neck positions with two other normal single coils, the middle position between neck and middle basically had very little volume. What would be the reason for this?

[Mark Hammer]

I suppose i'm starting to understand all of this. If I'm wiring the two coils out of phase with each other, what does that mean exactly? Is it similar to wiring it in series?

They can be wired either way, actually. Of course the manner in which the dummy coil contributes to the overall inductance of the "pickup" (i.e., the whole assembly sensing the strings at the moment) will vary, depending on whether the dummy and active/string-sensing coil are in series or parallel. Neither is more "correct", just different.

Also, when I tried a noiseless pickups before, it actually worked pretty well. I used a bifilar core and just had the two separate coils wound opposite each other. However, when I put it in the neck positions with two other normal single coils, the middle position between neck and middle basically had very little volume. What would be the reason for this?

There are always several forms of cancellation going on when two or more pickups are engaged. Although we may think that a neck and bridge, or neck and middle, simply sum with each other, the reality is that the peak of a string's vibration may well find itself directly over one pickup, while the trough is over another. When those positive and negative half-cycles are summed, even though the pickups themselves are electronically "in phase", you get cancellations. One needs to differentiate between the pickups sensing an identical string signal in opposite fashion, and pickups sensing opposite string signals in identical fashion. The former generates deliberate cancellation, and the latter generates adventitious and serendipitous (and inconsistent) cancellation, but they are both cancellation.

The general principle is that the more alike two pickups are in what they sense, the greater the likelihood of electronic cancellation (assuming they are wired opposite phase). So, if a person wired up a normal Strat such that any pickup could be placed out of phase with any other, neck+middle and middle+bridge would result in a far thinner sound than neck+bridge; the reason being that what the neck and middle pickups detect is far more similar compared to what the neck and bridge pickups detect when both on.

So, when you have a bifilar pîckup in the neck position, and normal SC in the middle position, one of those bifilar coils is going to be out of phase with another pickup very nearby: more in common = more cancellation.

[John Carlsen]

Oh ok, that makes sense. So then, if I wanted to use pickups that used bifilar cores, then it would probably be better to use them with others of the same type rather than in conjunction with normal SC in order to achieve a more "normal" sounding position 2 or 4. Would this be at least a relatively accurate statement?

[Mark Hammer]

Or alternatively, use only one of the coils in the bifilar pickup, when in conjunction with another normal pickup. Remember that typical sets of 3 have the middle pickup RWRP with respect to the others so that hum cancellation occurs in switch positions 2 and 4. No reason why you couldn't do something like that too.

[John Carlsen]

So, I imagine that this would be where having it wired with 4 conductor wire would be needed in order to split up the coil.

So, is it really as simple as wiring it up like a humbucker? It's not really something that I want to market or produce for my business, but am curious about creating a good sounding noiseless for myself. I've pored over the patents for Kinman and duncan, but am just at a loss for how they are wired. Do you have any ideas about how this is wired? It looks like it's just a two conductor with a ground.

[Guitarist]

I think Heil microphones also use a noise canceling coil in-line with the mic element.

[Mark Hammer]

You can go here: Retrieving Patent from PAT2PDF.org - Free PDF copies of patents: Download and print!

and enter in the number for Kinman's pickup patent: 5,668,520

That should explain the wiring of his.