Tapped coils (not split coils)

[Chuck H]

First... It's surprising to me that there is almost no information about this possibility doing the regular searches here and abroad. If I search for coil taps I invariably get nothing but info about coil splitting and switch options for distinctly NOT coil tapped humbuckers. Which makes me wonder why the terms are fuzzy for so many people.?.

Is anyone doing this? One thing on my wish list is a p90 sized humbucker that has tapped coils. In a perfect world it would sound like a filtertron in one selection and a hot paf wind in the other. I know these pickups are different in other significant ways so maybe a design that averages some parameters to at least hint at these two tones.

I asked after this here before but I don't remember it going very far. Right now there's a thread on the general forums about the lower activity level here on the pickup forum so I thought I might re introduce the subject and hope for the best.

TIA

[Helmholtz]

So the question is: Who makes this? I.e. a P 90 sized HB with tapped coils?
Makes me think of Gibson LP de Luxe mini humbuckers (regarding tapped sound).

[Chuck H]

So the question is: Who makes this? I.e. a P 90 sized HB with tapped coils?
Makes me think of Gibson LP de Luxe mini humbuckers (regarding tapped sound).

Well, a p90 sized humbucker can be had. And I think there are a couple of tapped coil full sized humbuckers available. Pretty sure a p90 sized tapped coil humbucker would be a custom job. But probably nothing a couple of the guys here aren't up to. I was really just opening it up as a topic for discussion. And if anyone here thinks a filtertron-ish/paf-ish sound from a tapped coil p90 sized humbucker is possible, well it wouldn't be bad (for me) to have an idea what that might cost.

Were the LP De Luxe mini's tapped? Or do you just mean to say they have a lower output than a paf? And I do think the p90 and mini's are a different size. I'm pretty sure you can get p90 type frames that fit a mini humbucker though.

[vintagekiki]

Do you think about tapped (coils) PU?
https://www.flyguitars.com/gibson/bass/LesPaulTriumph_circuit.php

http://images.gibson.com/Lifestyle/Support/Files/Schematics/LPTriumph-RecBass.PDF

[Helmholtz]

Were the LP De Luxe mini's tapped?

It isn't. But its lower impedance and its form factor (-> aperture) might give an idea what a tapped p90 shaped humbucker might sound like.
(But I just remembered that it has considerable Eddy losses caused by the brass cover and the bar steel core - so that could be improved for more brightness/more pronounced resonant peak).

[Chuck H]

Well I'm really just hoping a discussion starts here regarding tapped coils for pickups in general. Seems like a little exploited possibility for winders. But since it's on the table, I have nice. bouncy, ringy sounding LP Special that has those awful p100's in it. I'll probably go with a p90 for the neck. For the bridge I think a pickup that could go from being filtertron-ish and switched to a hotter type humbucker sound would make it a very versatile and fun guitar. I could go from Malcolm to Angus with a switch. Well... A switch and a lot of practice

[Mick Bailey]

What about winding a tapped coil with two wire gauges? Inner winds thicker/fewer turns, outer winds thinner/more turns - to give an overall DCR the same as a regular coil but either tapped section would give two very different sounds. I like the sound of a low DCR pickup - I've wound a few Tele neck pickups with #42 and the sound really bright and clear. I haven't thought this through and it's likely it's an old idea that's been done thousands of times.

[Helmholtz]

I like the sound of a low DCR pickup - I've wound a few Tele neck pickups with #42 and the sound really bright and clear.

Did the PUs you compared all have the same total number of turns?

[Helmholtz]

There is a drawback with all tapped PUs, we discussed the effect here:
https://music-electronics-forum.com/...-makers/47186-

In post #39 I wrote:

When using the tap as output, the disengaged part of the winding is still there and remains to be inductively coupled with the rest of the coil. It becomes the secondary of a transformer. This secondary appears to be open but is actually terminated by its own self-capacitance. The latter gets transformed/reflected to the primary side (the active part of the coil). And thus the reflected capacitance of the secondary adds to the capacitance of the primary - as long as you don't physically remove the disengaged part of the winding from the pickup.

This effect does not depend on electrical connection between the coil parts.

From post #67:

My general resume regarding tapped singlecoils, based on theory and the measurements of Antigua, is that tapping inevitably introduces unwanted additional capacitance in the active coil and thus tends to prevent getting really different sounds (i.e. resonant frequencies) from different configurations (full vs tapped).

And #74:

My point is, that the unavoidable inductive coupling between the winding parts prevents a tappable overwound SC from convincingly reproducing the brighter sounds a a lower or "standard" wound PU, no matter how you split the coil or separate the windings, as the unused part of the coil always increases the effectice capacitance across the active coil by a considerable amount. As a result the two sounds available won't differ much - except when using very long guitar cables. But find out yourself.

[bbsailor]

Here is something to keep in mind to form a good mental model of pickup loading. Typical high impedance pickups use what I call the “rule of 40” to match the pot load to the pickup resistance. Pot resistance loads are about 40 times higher than the DCR of the pickup with single coils having 250K volume pot values and humbuckers having 500K pot values.

This rule of thumb also implies that the typical 1Meg ohm amp input impedance is also in parallel with the volume pot values. The 250K pot in parallel with the 1Meg amp input impedance is 200K pickup load while the 500k pot has a 333K pickup load. When you add the coax cable capacitance which is about 10pf per foot, you add another variable to the sound you hear due to the capacitance effect at a higher input impedance.

When I made my low impedance pickups using a current transformer to target the typical XLR mic input, 3 pin balanced line that today has an actual load of 2400 ohms. By using a maximum output impedance of the pickup to being one tenth of the load impedance, the typical rated mic of 150 ohms may have an actual output impedance near 250 ohms. This is why the length of the low impedance mic cable, 10 ft, 25 ft, up to about 50 ft has minimal effect on the mic tonal changes. Change a guitar cable from 10 ft to 20 ft and you will hear a change.

One easy way to get around this is to buffer the pickup output impedance so that any external load will have minimal tonal effects on the guitar sound, but it requires an active circuit inside the guitar and a battery inside the guitar.

A good alternative is to put the high impedance buffer with a 2 to 10 meg ohm input impedance inside the guitar end of a metal quarter inch guitar plug with the power being fed into the amp end of the same cable, using either 9V battery or a plug in power supply. At the lower impedance and the isolation of the pickup from the capacitance load variations, changing cable length has minimal or no audible effect.

Here is a thought experiment. If you wound a tall single coil pickup, how is the induced voltage from the moving guitar string above the pickup magnet distributed between the upper winnings and the lower windings turns?

Answer: The higher turns produce more output than the lower turns. The Aumitone pickups use high location of the metal pickup frame as a single turn coil being inductively coupled to a pair of many thousands of turns on smaller coils using very fine wire which effectively puts most of the pickup turns very close to the strings and thus makes up for any inductive losses or inefficiency in current transformers working at low levels. If you look on the side of the Alumitone pickup you will a laminated C shaped transformer core intersect the aluminum pickup frame and then go through two side by side coils wound with enough very fine wire to have an output resistance near 2.5K ohms with the coils being wired in parallel.

While we can examine our advanced knowledge of pickup theory today, the early pickup makers had only one measuring tool…their ears and the output level needed to drive their early amp design input circuits with the required pickup output levels. Today we have current transformers, that when applied to guitar pickups we can make a new style of pickup that is governed by coil turns ratios, inductive coupling, and the skin effect of using either a solid single turn or a stranded single turn to affect the tonal output. This should open a new era for experimentation. Use current transformers with multiple outputs or wind the primary turn through multiple current transformers and listen to the output when multiple transformers are wired in series, parallel or single.

Joseph J. Rogowski

[Mick Bailey]

Did the PUs you compared all have the same total number of turns?

No - slightly fewer turns when wound to the same bobbin capacity on account of the larger wire (#42 as opposed to the original #43). The first time I did this was described here in post #8; https://music-electronics-forum.com/...stance-problem

[vintagekiki]

http://zerocapcable.com/?page_id=400
The Guitar Pickup Tone Database

[vintagekiki]

https://guitarnuts2.proboards.com/thread/7723/measuring-electrical-properties-guitar-pickups
Measuring the Electrical Properties of Guitar Pickups

[Helmholtz]

No - slightly fewer turns when wound to the same bobbin capacity on account of the larger wire (#42 as opposed to the original #43). The first time I did this was described here in post #8; https://music-electronics-forum.com/...stance-problem

Thanks, so the main reason for the brighter sound with #42 wire might have been lower inductance and thus higher resonant frequency.

[vintagekiki]

Logical
Same bobbin capacity, thicker wire, less turns, lower inductance, higher resonant frequency, brighter sound.