A really really thin mag pickup

[Mark Hammer]

So, I have this delightful Kalamazoo arch-top from the mid-to-late 30's that I've always wanted to mount a pickup on by the neck. Unfortunately, the guitar was never designed around the possibility of adding a pickup so the strings lie very close to the body at the end of the fingerboard. I've searched high and low, and there is simply nothing commercially available that would fit in the available space. Seriously, I have looked hard. Any of the slim profile pickups intended to attach to the end of the fingerboard would likely need to be positioned halfway between the fingerboard and bridge before they'd even begin to fit under the strings.

So, it became clear I was gonna have to wind my own. I think I finally have the materials to do so. I have some very thin 1/4" ceramic button magnets (presumably intended for use on efrigerators, holding up school notices and phone numbers), polarized in the direction I need, and some distressingly thin (but rigid) copper-clad board for making PCBs. If I sandwich the magnets between two pieces of copper board, the height, while unsuitable for virtually anything else, will accommodate a coil that actually fits under the strings.

Here's my question: Assuming I have the copper side facing towards the coil (magnet tops not exposed through the copper), and wind the coil directly around the button mags, am I gonna have anything worth listening to? Keep in mind that I have a choice of any wire gauge between #38 and #44, and since the goal is to use it as a jazz guitar, I'm not looking for crystalline highs (think Grant Green tone, rather than Tuck Andress). As well, given that it will not involve any routing at all (affixed via adhesive), it can be any coil width I damn well please. Would I be better taking the time to stick the copper board in etchant and take the copper off (at least the top piece of flatwork)?

[salvarsan]

Hail, Marcus.

Plan D is to wind a skinny/flat low impedance pickup with big wire (#28-#32?)
and run it to an impedance matching transformer at the amp.

The low impedance coil is much more immune to electrical noise.

-drh

[bbsailor]

So, I have this delightful Kalamazoo arch-top from the mid-to-late 30's that I've always wanted to mount a pickup on by the neck. Unfortunately, the guitar was never designed around the possibility of adding a pickup so the strings lie very close to the body at the end of the fingerboard. I've searched high and low, and there is simply nothing commercially available that would fit in the available space. Seriously, I have looked hard. Any of the slim profile pickups intended to attach to the end of the fingerboard would likely need to be positioned halfway between the fingerboard and bridge before they'd even begin to fit under the strings.

So, it became clear I was gonna have to wind my own. I think I finally have the materials to do so. I have some very thin 1/4" ceramic button magnets (presumably intended for use on efrigerators, holding up school notices and phone numbers), polarized in the direction I need, and some distressingly thin (but rigid) copper-clad board for making PCBs. If I sandwich the magnets between two pieces of copper board, the height, while unsuitable for virtually anything else, will accommodate a coil that actually fits under the strings.

Here's my question: Assuming I have the copper side facing towards the coil (magnet tops not exposed through the copper), and wind the coil directly around the button mags, am I gonna have anything worth listening to? Keep in mind that I have a choice of any wire gauge between #38 and #44, and since the goal is to use it as a jazz guitar, I'm not looking for crystalline highs (think Grant Green tone, rather than Tuck Andress). As well, given that it will not involve any routing at all (affixed via adhesive), it can be any coil width I damn well please. Would I be better taking the time to stick the copper board in etchant and take the copper off (at least the top piece of flatwork)?

Mark,

Please carefully measure and post all your constraint measurements. ALNICO magnets can be obtained that are .250" dia X .250" tall to play with matching to a miniature transformer in the 8/16 ohm to 20K/50K range. Radio Shack has some 3/16" dia X .125"?? or .0625"?? thick magnets that will also work.

How do you plan to mount the pickup to the guitar?
Drill any holes on the side of the neck?
Double face tape?
Secured to pickguard?

If you want to mount a volume and tone control on the pickguard you need to measure the available space so you can consider whether a small transformer can fit under the pickguard or must be mounted on the amp as drh suggests.

One consideration is to attach the pickup to a custom pickguard so the thin magnet wire can be led to edge pots for volume and tone as well as a potential matching transformer with copper tape over the thin wire leads to protect and shield.

Post a photo of your guitar, neck end view and max pickup height measurement so we can see the type of space you have to work with.

Just off the top of my head, 150 to 200 turns of AWG 30 or 32 will match to an 8 or 16 ohm transformer using ceramic magnets. If ALINCO magents are used, you can use less turns and a little thicker wire.

Joseph Rogowski

[WolfeMacleod]

Want a thin pickup? You can make one from a credit card.

[Rosewood]

Want a thin pickup? You can make one from a credit card.

How so?

[Possum]

what about DeArmond

What about the DeArmond "monkey on a stick" pickup? They use really short magnets, they aren't horribly expensive and there a ton of them on ebay.

[Sweetfinger]

My goto pickup for ultra-thin needs were the Dearmonds from Harmony Stratotones, although now, they're getting kinda spendy. 2nd choice would be the really thin Barcus Berry things made for resonators or flat top acoustics. If you're winding your own, you'll likely end up with something vaguely like one of those two.

[WolfeMacleod]

How so?

It was in 1996 that I first learned about it from a local pickup maker who runs under the radar. Very small time, no internet presence at all.
I don't recall the specifics, but I should be paying him a visit soon to return a 50's P-90, so I can ask him when I see him.

[David Schwab]

Mark, I think those refrigerator magnets might be too weak. I tried some of those types of ceramics out for my very couple of attempts to make a pickup and they were just too weak.

Copper clad circuit board works fine for flatwork. I made a Tele bridge pickup using some double sided PCB.

If you wants really thin, try some of those small neo magnets. The super small ones they sell in RadioShack aren't strong enough on their own, but I think some 1/8 X 1/8 might work.

Some of those old DeArmond pickups were quite thin. They are pretty simple designs. Just some magnets (or magnet) between two thin plastic like sheets, with very thin wire.

[Mark Hammer]

Thanks for the replies, and the tone of concern evident in the posts. Much appreciated, gents.

There's thin and there's thin. If I install near the fingerboard, I have maybe 3/32 to work with before pick starts to touch pickup. I have looked at all the thin-profile PUs people mentioned, and ended up wistfully thinking "Man, if ONLY I had another 1/16" to play with!". When I say nothing fits there, I mean it, baby. Quite simply, the folks in Central Michigan were NOT thinking about folks adding a pickup to this in 1937. Even were I to contemplate cutting a hole in the top and sinking a regulation-size Charlie Christian style or even PAF in it, the mounting ring would still have too high a profile. I'll see if I can post a pic, though an emergency mobo transplant seems to be needed this evening and might delay any pic-posting.

Attachment to a custom pickguard is a quite suitable idea. I can easily make the bottom piece of flatwork longer on the treble side than the top piece, to affix it to the pickguard, and I have a nice hunk of tortoise-shell pickguard material left over from a 1982 visit to the Parsons St. facility (now Heritage Guitars), so I have the materials I need. I guess the concern would be assuring that the pickguard lays flush enough against the body near the high E to permit the attached pickup to lay as flush with the body as possible. I can't really afford another millimetre of clearance to be squandered.

I've pondered neodymiums. I live right near Lee Valley Tools headquarters, and they have a broad assortment of neo's in tiny sizes. With the proximity of the magnets to the strings, though, I'm more than a little concerned about the effect of too-strong magnetic tug on sustain. Now, granted that use of said instrument as a "jazz" guitar suggests a willingness (though not eagerness) for notes to die a quick muffled death, I'd still like to maintain what sustain is in the instrument. So, in the tug of war between neodymiums and too-weak ceramics (these seem pretty strong, even though I haven't measured them), I can always figure out an electronic solution to signal quality and optimizing S/N ratio if I go with ceramic, but I'm not so sure I can get back my sustain if I go the neodymium route.

Thickest wire I have in any appreciable quantity is #36, and below that is #22. I can try winding a modest coil with the #36, as suggested, and try to locate a suitable upward matching transformer. I have one or two of the 1k/8r transformers from Radio Shack, but I gather the goal is to have the higher impedance side be higher than 1k?

[chevalij]

Any way to position it inside the body?

[Mark Hammer]

Hi Jeff,

Sadly, nope. I suppose one could try and sneak it in via the F-holes, but that would be a big production and not assured of success. Great guitar, I have to say, but just not pickup-friendly AT ALL.

[salvarsan]

There's thin and there's thin. If I install near the fingerboard, I have maybe 3/32 to work with before pick starts to touch pickup.
...
I've pondered neodymiums. I live right near Lee Valley Tools headquarters, and they have a broad assortment of neo's in tiny sizes. With the proximity of the magnets to the strings, though, I'm more than a little concerned about the effect of too-strong magnetic tug on sustain.
...
Thickest wire I have in any appreciable quantity is #36, and below that is #22. I can try winding a modest coil with the #36, as suggested, and try to locate a suitable upward matching transformer.

Magnets
The size makes the strength, so with neodymium mags, go thin and narrow.
.188"dia. x .062" thick buttons or 2"x.25"x.062" bars are an obvious choice.

http://www.kjmagnetics.com/proddetail.asp?prod=BY041

With either ceramic or neodymium magnets, try mounting the coil in
a U-shaped soft steel channel to focus the magnetic field. More diffuse
magnetic field on the strings, more bass, more output that way.

Transformers
The RatShack low->hi-Z transformers list spec as 300 ohms to 30k
impedance (not DCR) but you can get acceptable results with different
input device impedances. This transformer is in an XLR to 1/4" phone
adapter, BTW.

You can probably use any generic low->high-Z microphone adapter,
such as from Shure.

-drh

[bbsailor]

There's thin and there's thin. If I install near the fingerboard, I have maybe 3/32 to work with before pick starts to touch pickup. I have looked at all the thin-profile PUs people mentioned, and ended up wistfully thinking "Man, if ONLY I had another 1/16" to play with!".
Thickest wire I have in any appreciable quantity is #36, and below that is #22 I can try winding a modest coil with the #36, as suggested, and try to locate a suitable upward matching transformer. I have one or two of the 1k/8r transformers from Radio Shack, but I gather the goal is to have the higher impedance side be higher than 1k?

Mark,

Given those constraints which are a little slimmer than I thought, here is a plan.

Obtain three dual magnet packages 64-1895 from Radio Shack. These are actually two rare earth disk magnets per pack that are 3/16" dia by 1/16" thick.

Use a plastic humbucker bobbin as a spacer to place the magnets on a piece of thin plastic, like an old credit card with each magnet super glued in alignment under the strings. Place an alignment mark, then glue the first magnet. Once that dries and is secure, glue the next magnet. The magnets, if loose, will want to flip. Make sure the same pole is facing the strings on all six magnets that are glued. Then place the top plastic piece on top and glue that to use the magnets and plastic to make an ultra thin bobbin.

You can get about 10 turns of AWG36 on one layer through the width of the thin bobbin. AWG 36 is .414 ohms per foot. One turn is .159 ohms. One layer, 10 turns is about 1.59 ohms. Assuming you fill the bobbin to 3/16 from the center you will have 37 layers. That makes the coil 1.59 ohms X 37 or 58.8 ohms. You could feed this into a Shure A95U matching transformer with the internal jumper moved to the low impedance setting and obtain a good output equivalent to about 9600 turns of wire on a bobbin considering the voltage gain of 26 on the A95U.

My mental modeling suggests that the outer windings may not be in as strong of a magnetic field as if the magnets were longer, but this should work pretty well and if wired as a balance line to the transformer, should have a relatively low noise and thus afford a little more amp gain.

Once you get this stage made, post your results and I'll walk you through some other ideas about securing it to the pickguard. Make sure you have about 1/16 of an inch from the wire to the edge of the plastic bobbin so a plastic shim can be added to each end to affix the bobbin to a pickguard cutout that will secure the pickup without adding any more height. Make sure the bobbin is 1/16 wider on each bobbon end or a total of 1/8" wider than a standard humbucking pickup bobbin. Keep the bobbin ends square rather than round. This will make mounting to the pickguard a little easier.

I hope this gets you started.

A little after post thought: Look at the magnets recommended by drh as that will be easier to glue to the plastic end pieces making the thin bobbin. All other winding ideas should still work.

Joseph Rogowski

[David Schwab]

I've pondered neodymiums. I live right near Lee Valley Tools headquarters, and they have a broad assortment of neo's in tiny sizes. With the proximity of the magnets to the strings, though, I'm more than a little concerned about the effect of too-strong magnetic tug on sustain.

There's really nothing to worry about. I use some 1" X 1/4 neos in my pickups. I usually use two of them. They are crazy strong... it's tough to separate them. I haven't had any issues with string pull when used in a pickup.