Pickup String Spacing – choosing a humbucker

 

Pickup string spacing is something you need to be aware of when you’re buying guitar pickups, particularly humbuckers. Guitar bridges come with different string widths so pickups need to match that. In this blog post I’m going to explain what It’s all about and how to measure it.

Table of Contents

What is a Pole Piece?

What you don’t need to know

Pickup String spacing – what you need to know

How to measure string spacing

What is F spacing?

What is a Pole Piece?

Pickups have pole pieces, think of these as magnets mounted in the pickup listening for string movement. Sometimes they are actual magnets, sometimes pieces of steel directing magnetism towards the strings. In this case they are steel screws.

This is what we mean by ‘pole spacing’ its the distance between the outer most poles, centre to centre.

What you don’t need to know

The way a pickup works is the string sitting inside the magnetic field actually becomes a temporary magnet and when it vibrates it disturbs this magnetic field and creates an electrical signal in the coil of wire around the magnet.

It’s a tiny signal but enough to get through your guitar’s on board circuit and down a cable to an amplifier. It’s hard to imagine that such a small amount of electricity can produce such a lot of sound. Have a think about it next time you’re at a big gig. What you’re hearing is just that small amount of electricity generated in a coil of wire. It’s really cool stuff and I find it fascinating. But you don’t really need to know all that.

Pickup String spacing – what you need to know

What you do need to know is that the string needs to align with the magnet to get the best signal. Magnets are, however, not lasers, they generate a magnetic field and not a precise beam. If the string isn’t in perfect alignment it’s fine. If the slightest misalignment made a difference then string bending would cause a drop in volume. Have a look next time you bend a string how far the string moves away from the pole.

As you can see, a little bit out of line makes no difference. Eddie Van Halen used a vintage PAF on Van Halen I with a Fender type bridge – the PAF ‘s were 49.2mm (1 15/16″) spacing and Fender bridges are usually 52mm. If there had been a problem he would have noticed.

Please remember that if a humbucker has 49.2mm spacing or 52mm spacing it’s outer dimensions are the same. The overall size of the pickup doesn’t change. So if you take out a 49.2mm humbucker and replace it with a 52mm it will still fit, it’s just the pole alignment to the strings that will be different.

Guitar bridges come in various sizes giving different string spacing. So if you have a Gibson ABR Tune-o-matic your string spacing will be narrower than a Fender Strat bridge, for instance.

By the time the strings get to the neck pickup the spacings are just about the same so neck pickups don’t vary in width. We’re just talking about bridge pickups here.

So we really want the strings to line up as best as possible with the pickup’s poles but we’re not getting too hung up on it.

How to measure string spacing

The measurement is the distance from the first to the sixth strings centre to centre at the bridge pickup. This diagram should help:

You can simply do this with a ruler, like I have.

As you can see this ’89 Strat bridge has 52mm string spacing. If you wanted to choose a bridge humbucker to make it a HSS Strat than choose the 52mm option.

If you’re buying a Mr Glyns Pickup and have any doubt just send me a pic of your bridge and I should be able to advise you.

What is F spacing?

F spacing simply means a wider spaced bridge humbucker – 52, 52.5 or 53mm. The F stands for either ‘Fender’ or ‘Floyd Rose’. It isn’t clear which and doesn’t really matter.

Why 49.2mm not just 49mm? You may well ask! It’s the metric equivalent of the pole spacing for a Gibson PAF which is the pickup most humbuckers are based on. The original measurement in imperial is 1 15/16″ – which if you ask me is no less silly a number that 49.2 but we’re stuck with it.

If this has given you a need for a new set of humbuckers you can find the Mr Glyns Pickup humbucker range here.

Here is a link to my YouTube playlist for humbucker demos.

Hamurana Guitars NZ

 It’s always interesting to see where my pickups end up, in this case Hamurana Guitars NZ.

Hamurana Guitars

They make World class guitars combining looks, playability and tone. I’ve played a few – they are outstanding.

Hamurana have used my pickups in a few builds and it’s always great to see what he comes up with. This time he’s used a pair of my my Black Sand humbucker size P90’s.

You can get in touch with Hamurana Guitars and order your dream guitar here:

https://www.hamuranaguitarworks.co.nz/

Here’s more info on the Black Sand pickups:

The humbucker sized P90 is a great pickup – it sits tonally between a humbucker and and a strat type pickup. If your neck humbucker is a bit thick and woolly sounding for you, you want more clarity, or just want a different tone, then this one may be the answer. The physical size of this pickup is identical to that of a “normal” humbucker so it will pop straight in.

P90’s are different to other single coil pickups. They have a wide, flat coil similar to that of a Jazzmaster but the magnetic field is a very different shape. Fender single coil pickups have the coil wound around the magnet giving a focused, precise percussive sound. A P90 has 2 bar magnets underneath the coil; this broadens the magnetic window allowing the pickup to listen to a bit more string and thickens the sound. I chose Alnico V bar magnets for this model to help give some grit and power characteristic of a P90.

Of course, too much power and the pickup would sound too thick and bass heavy which is not its purpose. Too little power and it just won’t snarl.

Humbucker sized P90s are such a useful pickup. They sit tonally between a single coil and a humbucker (roughly speaking). and their physical size means they pop straight into any humbucker equipped guitar.

The development of my “Black Sand” pickup was a bit backwards. Usually I make a bridge pickup first and work from there but with this one the neck pickup came first. I had a customer ask for a neck pickup for an es335 to sound clearer than his existing Gibson humbucker. I sold a few neck pickups before thinking it would be a good idea to have a set. So I started work on the bridge pickup.

I wanted this bridge pickup to have clarity in the lower mids to stand out from humbuckers while having enough power to grit up nicely. I wanted it to be clean when tickled and to growl at you when you dig in. P90’s are all about dynamics. It had to match the existing neck pickup or work well as a stand alone in a HSS situation.

Of all the pickups in my range this one came together the quickest. There were only 4 or 5 prototypes and I was happy. Experience and intuition combined with a notebook where I’ve written down details of every experimental pickup I’ve made since 1995.

There were a load of prototypes in and out of a Les Paul, Tele Delux and PRS, through different amps and in the hands of different players. I never trust just my own ears with my pickups. I like to get opinions and suggestions from a few players before making any final decisions. I listen to what players say and I adjust prototypes accordingly, but at the end of the day the final decision is mine. I’m always aware of the phrase “a camel is a horse designed by committee”.

It took a while to get this one right. A pickup would sound great at workshop volume, them I’d play it in a band situation and it would be too boomy, too much like a humbucker. So I’d have a think and make another. In the end persistence paid off.

The pickups I finally settled on went into my Les Paul and off to a gig for the ultimate test, and that’s where they’re staying.

The neck “Black Sand” is a great match for either my “Integrity” or “Cloud Nine” bridge humbuckers or as a set with its equivalent “Black Sand” bridge humbucker sized P90.

I agonised over what to call this pickup set. I wanted a name that would reflect the apparent contradiction in P90’s. From the perspective of a humbucker player they are clear and chiming. From the viewpoint of a single coil player they are powerful and gritty. They’re one thing while looking like another. I wanted a oxymoron to reflect this contradiction, one that might include the unique magnetic structure that gives the P90 its character. So I went for a run along Muriwai beach to think. And there it was staring me in the face (literally). Muriwai has black volcanic sand due to its iron content and it’s magnetic. So I’ve called this set “Black Sand”.

I’m very happy with this pickup – hopefully you will be too.

Mr Glyns Pickups

Reducing hum - Shielding

It is very common for electric guitars with single coil pickups to hum. Humbucking (double coil) pickups get their name from their ability to get rid of hum. A typical 'Strat' pickup will have over 7000 turns of wire on it. I've never worked out how many kms that is but I'm sure its a long way. This much wire makes a pretty good antenna. There's a lot of electromagnetic interference flying about in the air for this antenna to pick up. Electric devices such as fridges and strip lights are particularly bad for this. Not only can these man made items cause problems but so can cosmic background radiation. This is the radiation present all over the universe caused by the Big Bang - known as the shadow of the big bang. Its been around for nearly 14 billion years just waiting to get into your pickups. The way to reduce this hum to an acceptable level is to in case all of the guitar's electrics in a metal box and earth that box. That way all the interference will be cancelled out to earth before becoming a nuisance.

Incidentally - this is how humbuckers do it: An electric guitar pickup is simply a magnet with a coil of wire around it. When something ferrous (a steel guitar string) is passed through the magnetic field is disturbs the magnetic flux and causes electrons in the wire to flow - this is of course electricity. But its not much electricity which is why we need to amplify it if we wanna ROCK. The signal produced is a sine wave (AC current) with peaks and troughs co-inciding to the string moving closer and further away. Imagine two pickups producing two sine waves with peaks and troughs at the same time. If we swap the wires around on one of these pickups a peak will occur on one at the same time as a trough is on the other. These signals are out of phase and almost cancel each other out. But they also cancel any hum. This is great - no hum - but also much less sound and a funny nasal one at that. Now the clever bit is with the magnet. One coil is given a North pole and the other a South.This puts the pickups out of phase again and therefore back in phase. They are electrically 180 out and magnetically also 180 out. The result is two coils working together with almost no hum.

It this case I am screening a Kramer bass. It has one single coil pickup which the customer is not happy with. It has such a low output as to be almost unusable. He's taken it to a repairer before who recommended an outboard pre-amp to boost the signal. The pre-amp has made it louder but with the gain right up has also boosted any hum. I've decided to go to the root of the problem and re-wind the pickup as well as fit another magnet. I've suggested to him that while all the electrics are out and the pickup is in bits I also screen both the cavities and the pickup coil. This way he will have not only a better sounding and louder pickup but almost no hum. And of course he's now got a pre-amp he can sell to help pay for it.

The body had no screening at all. The pots and jack socket have a small piece of foil on the plate but its not really going to do much good as a screen. I've slackened the strings off to get the plate out but there's no need to take them off. This saves time and also string breakage.

The cavity is screened by lining it with copper foil. Several pieces need to be cut and I make sure they overlap. The idea is to make a box. The foil I use has a sticky back which is also conductive so that each touching piece connects. I don't quite trust this so I also solder each piece together.

As you can see I make sure it folds over to connect with the screen I'm going to put on the underside of the pick guard. Although the pick guard is bolted to the pots which are earthed I take no chances and solder an earth wire to the screen and this wire in turn gets soldered to the pots.

So the completed body screening looks like this. I've kept is as neat as possible and left no gaps. Of course not all guitars are as easy to do as this one - Strats are a bit more complicated and of course its usually Fenders that I have to do this job on.Its unusual for a manufacturer to do a good screening job.

The screen on the underside of the pick guard completes the box. I use aluminium foil for this and cover the whole plate. The electrics are bolted directly to it so there's no need for an earth wire.

I don't cut this foil to size before sticking it on because its so much easier to do after. I use my knife as a scraper. I run it along the edge at an angle which scrapes through the foil. I then peel off the remainder and its undetectable when you screw the plate on. The same goes for the pickup hole.

So here are the finished items. They should fit together well and made a good earthed box. I often see black carbon spray on shielding used in cavities on production guitars - its not a patch on doing it this way. So that's the bulk of the electrics sorted, now its on to the pickup.

Kramer have used a large single coil pickup on this guitar. Its very similar to a P90. I have already re-wound it to give it a bit more oomph. I've potted it in wax and wrapped the coil in some tape to protect it and as an insulating layer between the coil and the screen. I'll go through the winding process another time.

Its back to the copper foil. I first cut the foil to the correct width and then wrap the coil with it. It is very important not to loop it all the way around the coil. A loop of wire is an antenna which would have the opposite effect. I leave a couple of mm gap to make sure it works properly as a screen.

Again I run an earth wire from it and to the back of the pots. A lot of care needs to be taken soldering onto the pickup. The windings are delicate and the insulation on the pickup wire

can easily melt causing a short circuit. I've just wound this one so I could wind it again - but if it was a vintage Fender...

Now its just a case of wiring in the pickup and the extra earths, tuning it, setting the pickup height, testing it all and calling the customer. I wonder if he's sold that pre-amp yet.

Here are a few more pics to show you how screening looks in a Strat:

Cheers,

  Glyn

I am no longer repairing guitars - I now work full time making pickups

www.mrglynspickups.com