Centre tapping a single coil?

[peskywinnets]

Just wondering if anyone had tried this?

If my comprehension is correct this would yield a humbucker in a single coil size?

Downside is ...it must be a right pain in the backside to solder a centre tap halfway through the wind?!

Anyone done it ...I'm tempted to have pop just for shits & giggles.

[Kazooman]

I Don't Think So

Caveat: I have never wound a pickup in my life.

That said, My simplistic understanding is that the coils of humbuckers are wound in opposite directions so that any signal from the stray electromagnetic radiation they may encounter is out of phase and cancels out. However, the polarity of the magnets for the two coils is also opposite. This makes the signal from the strings in phase and in simplest terms it is additive.

I don't see how you would get that from a center tapped coil, even if you reversed the direction of the winding at that point.

I am certain that the pickup winding gurus will chime in on this and give you a better (or perhaps correct ) explanation.

[peskywinnets]

Well, I'm pretty sure I have the theory right - a perfectly 'centre tapped' coi (centre tap grounded) will yield two signals 180 degrees out of phase (I'd need to combine them into one in a cct)...I'm more challenged by the winding aspect (but i now have a cunning plan for that bit!)

[Mike Sulzer]

Well, I'm pretty sure I have the theory right - a perfectly 'centre tapped' coi (centre tap grounded) will yield two signals 180 degrees out of phase (I'd need to combine them into one in a cct)...I'm more challenged by the winding aspect (but i now have a cunning plan for that bit!)

I do not think so. You need opposite magnetic polarity as well as electric. That implies two separate sensors with opposite magnetic polarity.

It is not so hard to make a tapped coil. Think about it, but it is not going to do you any good for this.

[peskywinnets]

I'm talking abot a pickup with differential outputs (+ve & -ve)....ie two 'hot' wires & one ground.

I'm making a bobbin for one of these right now...I'll let you all know how it turns out! Probably an epic fail!

[David Schwab]

Well if you take a stacked humbucker that uses a magnet that runs through both coils, like the old Duncan or an EMG-SA, then in essence it is a center tapped coil.

What you need to see is which way do you wire them up? I've made a few of these, and because I wound the top and bottom in the same direction, I needed to wire them out-of-phase.

But maybe if you are wring them to an op amp, you wont need to.

basically it's the EMG set up then.

[peskywinnets]

Probably worth mentioning, that I'm coming into pickup making with no previous experience, but I've no issues with electronic/electrical concepts like coil tapping, differential inputs/outputs etc - if that's what EMG do, then that'll do for me!

I'm reasonably confident it'll work ...though I can see why it might trip a few folks thinking it won't (ie because 'differential' outputs from a pickup isn't the 'norm') (& yes David, the coil will be wound in the same direction, with one single magnet running through the bobbin) centre tapped, with the 180 degree out of phase signals feeding into an opamp that'll combine the differential out of phase pickup outputs into one single 'hot'.

It'll allow me a nice small slim humbucker (which is what triggered my own particular 'light bulb above the head' moment in the first place!). Just knocked up this petite bobbin about an hour ago (well, two thirds of one at least!) ...

It's 10mm wide & 8mm tall (I didn't have any 8mm acrylic, so pressed some 5mm blue & 3mm black into service - the blue won't be seen once wound)

Later, I'll make a small PCB to allow easier hookup to the three 0.05mm(eek!) pickup wires.

[David Schwab]

I forgot that when you said tap, one coil would be inside the other... so I think just tapping the coil wont work, so try and do a stack. Now I see what Mike was objecting to. I was skimming. I was thinking stacks with one bobbin.

Here's what the EMG looks like on the inside. They are two separate coils. An alnico bar magnet runs through both coil.

You can also look at Duncan's patent 4524667 (below).

Just stick a thin divider in the middle.

The last picture is my Tele stack made from copper clad PCB.

[peskywinnets]

No, one coil won't be inside the other...essentially I'm winding one single coil, but at the halfway point, I stop the wind to add a centre tap - this then make it two coils the first will be 180 degrees out of phase with the second...probably best I just slip into my Nike T Shirt & "Just do it".

[Mike Sulzer]

Right, the stacked humbucker is just a single coil with a dummy closer than it ought to be wound the same cores. The bottom coil picks up less than the top coil because the core does an imperfect job of confining the fluctuating field from the string. There is still some signal cancellation, and the output is not very high. If you want a pickup with two coils that pick up signal in phase, you need to sense two regions on the string that are magnetized to opposite polarity. Then you get lots of signal. (I think what I wrote before was not clear; hope this is better.)

[David Schwab]

No, one coil won't be inside the other...essentially I'm winding one single coil, but at the halfway point, I stop the wind to add a centre tap

Yes, one is inside the other. Think about it, you are winding half of the coil, you take out a tap, and then wind more on top of that. So the first half of the tap is inside the second coil.

There were some patents on coaxial humbuckers like this. I never tried it so I don't know if it works.

But yeah, give it a try and report back!

[peskywinnets]

Damnit!

Being wet behind the ears I'd actually visualized this as two coils one on top of the other (which should work) but you're right, in practise this is actually one coil within another coil (this variant I'm not so confident about!) - oops.

Still, it's made now (bar the pole pieces!), I'll hover a sine wave from a sustainer driver coil over it in the next day or two to see what output I get from the inner & outer coil...



It's hard to see, but there are three wires there coming off if (a very faint purple wire in between the two red wires - which is the centre tap). Each coil has 1500 turns of 0.05mm wire & measures 1600 ohms DC resistance.

[Mike Sulzer]

The electrical polarity of a center tapped coil is +-+-. (The two parts are wound in the same direction.) You can connect the two ends to a differential (+-) amp, and the center to ground and get full signal, but it will not cancel magnetic hum. If you connect both ends to positive inputs you will cancel the magnetic hum, and most of the signal since the outer coil sees almost as much flux as the inner one.

Do so called coaxial humbuckers use magnetic shielding between the two coils?

[David Schwab]

Do so called coaxial humbuckers use magnetic shielding between the two coils?

That one patent seems to show something between the coils. It kind of looks like rod magnets.

[Mike Sulzer]

That one patent seems to show something between the coils. It kind of looks like rod magnets.

Interesting. I wonder if it is a fairly high permeability magnetic material such as ceramic. The idea would be to complete the return of the flux from the part of the string over the center coil inside the outer coil so that there would be little cancellation with the outer coil. It seems a bit difficult to do, but it ought to work. At a time when the humbucker patent was still in effect, it might have been a reasonable alternative.