Centre tapping a single coil?

[peskywinnets]

Sure, but that won't work with the bifilar coil you were using. The reason being that the two coils are mixed together and occupy the same space, so they both see the same magnetic field.

Yep, I'd figured that one on my own this time - I reckon this is like those magic eye pictures...you stare at the bar stewards for yonks saying "Nope, I can't see anything", then all of a sudden it snaps into 3D view & you can see 'em quickly after that - well, I've just had my magic eye humbucker moment this afternoon! (about 70 years too late)

[Mike Sulzer]

I would not call it a humbucker but rather a single coil with built in dummy coil.

Preamps have noise, whether they are in your guitar or your amp; if you play with high gain, you will notice more noise (hiss) if your pickup has less signal output. The best thing about a preamp is that it has a lot less capacitance at its input than a guitar cable does. Therefore, you can use lots of turns on your coils and not lose highs by lowering the resonant frequency of the circuit too much. IMO, the use of a preamp implies that you should measure the resonant frequency and adjust it by use of a cap to ground (and maybe a resistor in parallel) at the input of the preamp to get it to about 5 KHz, and then further adjust it for the sound you want.

Those diagrams aren't clear to my (untrained eye), & having just swallowed the concept to get humbucking you need two coils with opposing magnet polarities, can you please explain how it's possible to have a stacked humbucker with the poles running throughout the same two coils (is that what you're saying even?! )

One other bit of info (ie if it helps you guys pinpoint the best type of small humbucker for my needs!) - this mini humbucker pickup will feed into a preamplifier - so i don't need heaps of windings....the coils' signal voltage can easily be amplified onboard the guitar.

[peskywinnets]

Ok, points duly noted.

I was pondering something like the the coil mentioned in my last post (essentially one continuous coil wound onto the same bobbin, non bifilar, sharing the same magnetic polarity polepieces, but centre tapped halfway therefore yielding an inner & outer coil ...each coil yielding an unequal 'guitar signal' but equal 'noise signal' & with opposite polarities) into a summing amplifier. I've just lashed together this as a rough/quick outline...



(the pickup I've been winding is only 150 ohms per coil 'leg')

[David Schwab]

As noted by a few people, if both coils have the same magnetic polarity you will end up canceling out the strings as well as noise.

if you make a stacked coil, you can use the preamp and more-or-less have what EMG does.

[earthtonesaudio]

I kinda like the idea of an amplified dummy coil. Since the amplifier can make up the voltage difference you can get away with a much simpler coil (fewer turns, different size, etc). Think about that Suhr backplate system. If you took the same idea but used active amplification, it might simplify considerably.

[peskywinnets]

As noted by a few people, if both coils have the same magnetic polarity you will end up canceling out the strings as well as noise.

...but since the outer wound coil is further away from the overall 'core' (pole pieces), there won't be total cancellation of the guitar signal - but there will be with the noise ....& what signal I lose /through summing +ve string signal & (weaker) -ve string signal, I can likely be made up with the preamp - I'll give it a go.

Hmm...'dummy coil' - I'm not keen on that naming ... it suggests the coil is performing no role other than aesthetics, whereas it's a proper coil & fulfilling a really important role.... ie retrieving the 'noise signature' to be cancelled. But hey, as the new kid on the block, I'll roll with whatever it's called!

[Mike Sulzer]

Yes, the field from the vibrating string is guided down the pole piece, but a significant amount is lost along the way. Using separate cores with an air gap in between should give better isolation. And the rare earth earth magnets act almost like an air gap since their permeability is so low.

Putting the magnets on the bottom does not lead to more cancellation. The permanent magnetic field just magnetizes the string. If you put the magnets on the bottom, they just have to be stronger.

Tiny magnets on top work really well.

Yeah, how does that work? Is it a case of the non-uniform field that Mike Sulzer was talking about earlier?

As in, the music signal cancels, but because the two coils get different amounts of it, it only partly cancels? I'd have thought putting the magnet on the bottom of the stack would lead to more cancellation, hence less output than the SCN setup.

Thanks for posting the diagrams of the SCN, Dave.

[Mike Sulzer]

A core with magnetic permeability tends to guide the field lines through itself. This happens for both the signal and hum, not necessarily to the same degree, but I am not sure the difference is enough to make a good pickup.

...but since the outer wound coil is further away from the overall 'core' (pole pieces), there won't be total cancellation of the guitar signal - but there will be with the noise ....& what signal I lose /through summing +ve string signal & (weaker) -ve string signal, I can likely be made up with the preamp - I'll give it a go.

[David Schwab]

...but since the outer wound coil is further away from the overall 'core' (pole pieces), there won't be total cancellation of the guitar signal - but there will be with the noise ....& what signal I lose /through summing +ve string signal & (weaker) -ve string signal, I can likely be made up with the preamp - I'll give it a go.

It will be thin and clanky sounding, but by all means try it out.

You can also wire up a regular humbucker in phase and hear the same thin clanky tone, and those two coils are father apart.

Someone actually got a patent on a balanced output guitar.

[RedHouse]

No, if it sums the signal, it will sum the noise too. Can nae break the laws ae physics, Cap'n.

I smell shite!

Geez a break, hunners and hunners do, cannie hear the peckup say gonnaenodaethat?

[peskywinnets]

Got round to taking some screen scrapes this evening.

Here's a bifilar wound low impedance single coil, biased to VCC/2 via the centre tap, 40db of gain (100x for those not up on Db), summed with an instrumentation type opamp arrangement, noise floor ...




Ok, now the same coil, centre tapped removed from play, coil now biased via two low tolerance same value resistors (to vcc/2) on each side of the coil, 40db of gain, summed with an instrumentation type opamp arrangement, noise floor ...



Conclusion (ok, ok, which I/we knew already) - biasing a coil via two identical on its two end wires ain't nowhere near as good as good as bifilar wound coil biased via the centre tap.

By the way...the coil itself sounds "the bollocks of the dog" (that said, have you *ever* had anyone on here post a description of their own self wound pickup on here as being sh1t? But it really is akin to that "WTF?!!" type revelation wrt high end, mmediately after you've had your ears syringed)

[Steve Conner]

Nowhere near as good? The difference is only about 1dB. Try a FFT if your scope offers one.

What was the value of the resistors?

[peskywinnets]

Well put it this way, the audible hiss increases noticeably when the coil is biased via resistors (albeit listening through an amp sim, which will be applying significant gain of its own).

The coil is 80 ohms...I used 4.7k resistors to bias.

My scope app has FFT but the scope app crashes when I try to use it ...that'll be because I bought cheap 'n nasty from China.

[ForcedFire]

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.

I know this is a dead thread but I laughed so hard when I was reading the patent.

Seymour Duncan describing the Gibson PAF Humbucker: "The quality of the sound, the smoothness of the sound and the ability of the electromagnetic pickup to retain the sound is severly limited."

Hahahaha. Right...

[David Schwab]

I know this is a dead thread but I laughed so hard when I was reading the patent.

Seymour Duncan describing the Gibson PAF Humbucker: "The quality of the sound, the smoothness of the sound and the ability of the electromagnetic pickup to retain the sound is severly limited."

Hahahaha. Right...

He was not talking about the Gibson humbucker. The patent number for the Gibson humbucker is 2896491. That was not cited in the text.

He sounds more like he was talking about the stacked Les Paul Recording pickup as prior art. He starts at the end of the left column stating:

Electrical pickups manufactured and sold by Gibson Guitar Company in the early 1960s had an upper coil and a lower coil divided by a horizontal permanent magnet with the vertically extending openings in the coil completely filled with an iron load wherein one of the coils having the iron load was positioned in a spaced relationship from ferromagnetic strings on a multistringed instrument.

Then he further discusses that pickup by saying:

The use of a double-coil pickup, whether the coils are arranged in a side-by-side relationship or in an upper and lower relationship, provides greater flexibility in controlling the qualities of the sound produced by the multistringed instrument having strings formed of a ferromagnetic material. The known prior art devices are constructed such that an iron load or a unmagnetized ferromagnetic material is located within and fills the entire upper and lower openings of each coil.
Further, the coils are divided by either a permanent magnet member or by a magnetic pole piece having permanent magnets affixed thereto. The magnetic reluctance of the coil arrangement and the characteristics of the magnetic flux path are controlled solely by the magnetic pole pieces which are unmagnetized. Thus, the permeability of the "iron load," or the magnetic pole pieces, greatly affects the sound and quality of the electrical signal produced as an output signal in response to vibration of the strings. The quality of the sound, the smoothness of the sound and the ability of the electromagnetic pickup to retain the sound is severly limited.

So he's saying that he's using alnico magnets for poles, instead of steel poles.

You have to understand that to be granted a patent, you need to show novelty in your invention, and how it might be different enough from prior art.

But none of that had anything to do with the Gibson humbucker. This patent was for a stacked single coil pickup.