Making A Jazz Bass

Making The Pickups

Choices

I had already made a major choice, that I was going to make the pickups and I bought kits with Alnico 5 magnets. So, the remaining decisions were: Winding wire; Number of turns; Scatter setting on winder; Wire tension. I know that different pickups do sound different and there are plenty of opinions to be read, but they are just that and what constitutes better is subjective, there is no absolute better.

As for wire type, I had some 42 AWG enamel wire, solderable, (not enough as it turned out. I bought more.) I also have some 48 AWG wire which I used in making my slide guitar pickup. The thinner of these wires (48 AWG) gives about double the resistance of the thicker. I don't see that resistance itself has any bearing on the sound but the inductance of a coil using the thinner wire will be greater for a given coil and that will affect sound. Whether for the better or for worse, who knows. Certainly the slide guitar sounds OK to my ears. However, since this is a Jazz Bass copy, I will copy Fender and use 42 AWG.

I searched the Internet to get an idea of the number of turns that would be needed. I found numerous references, but little corroboration. Turns counts ranged from 8000 from the unwinding of a 1971 neck pickup performed by John Brown to the 10000 turns put on an over-wound neck pickup by Sullivan Music Equipment. Stewmac advises that 50's and 60's Jazz Bass pickups had 9500 turns. Being undecided, I chose to go with a tapped coil, 9500 turns, tapped at 9000.

There seems to be a general agreement amongst pickup winders that hand-wound pickups are "better" than machine wound. I'm sure Fender would not agree. The difficulty I have with hand-wound being better is that there cannot possibly be consistency between pickups. The reason given for hand-wound being better is generally attributed to scattered nature of the turns and it is the case that scatter winding gives lower inter-turn capacitance and may well result in more treble compared to a machine wound pickup. My home made pickup winder automatically advances the winding wire by a certain amount each turn and I have previously set this to the diameter of the wire. For these pickups, I set the it to 0.25  mm per turn. The wire diameter is 0.064 mm so it will certainly scatter the winding but it will also be entirely repeatable. I may be that this is too much scatter and the pickups may be too bright. I'll find out later. It is possible to imagine all manner of winding strategies, the advance per turn could change in any conceivable way throughout the wind. However, to make and try out different combinations is an enormous job, not to mention the difficulty in evaluating them. I wonder how much research has gone into the pickups of the major manufacturers?

Wire tension is yet another variable that is likely to affect the sound; lower tension meaning that the windings take up a greater space and inter-winding capacitance is reduced. To control wire tension, I clamp the wire between two pieces of felt covered wood , using a small G-cramp to apply pressure. I usually 'play it by ear' in deciding what is enough tension but after winding the neck pickup what I thought was, a little loose, I resolved to find a more reliable method. I made a wire tension-meter, a simple device whereby the wire deflects a beam according to its tension.

Having built the thing, I thought I should calibrate it.I tried to do this by hanging weights (8 mm nuts weighing 4.5 gramme each) from the pickup wire after the tension-meter but the results were not repeatable, there was too much hysteresis (or stiction). I think it is because of the friction between wire and the guides. However, with the winder running it does appear to provide a measure of the tension. I imagine that, with the wire moving and changeing speed as the pickup rotates, the hysteresis is overcome.

Here is a video of it in action. Notice how, when the G-cramp is adjusted, the measuring beam moves with little apparent hysteresis.

 

Assembling Magnets and Flatwork

20180319 120524I was not happy with the eyelets in the purchased flatwork,they stood proud of the flatwork and I feared they would snag the winding wire. Also I needed an additional eyelet for the coil tap. I removed the old ones and drilled three holes at the opposite end to take the new eyelets. I made a miniature counter boring tool to make a 3 mm wide by 0.5 mm deep counter bore (essentially a small flat bit) and counter bored the holes. The eyelet heads would then be below the surface. I was unable to source an eyelet setting tool, so I made one, along with an anvil.

20180319 125541I made a simple arbour to fit in the lever-press, just a 50mm length of 10 mm mild steel drilled 0.195 inch to accept the magnets. The eight magnets were installed in the bottom flatwork from the underside, chamfered end first and then pressed right through with the aid of a slotted block of wood. The arbour was turned round, to present its un-drilled end to the work-piece, then the top flatwork was pressed on to the magnets, progressing gradually across the pickup so as not to distort the flatwork. Once flush with the magnets, spacers were installed in the winding space, the arbour was reversed again and the top flatwork was pressed down on to the spacers, again progressing in stages across the magnets. I made the spacers 11.4 mm deep, so that the magnets would poke through the pickup cover and stand up by about 0.5 mm.

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Winding

20180328 120232The unwound neck pickup was fastened to the winder faceplate, string side out, and the settings were chosen and the limits of the winding width set. I first wound 500 turns, looped the wire thorough the tap eyelet, fastened it with tape, and then wound 9000 turns. Lead wires and winding wires soldered to the eyelets and the pickup dismounted. There we are, two sentences but about 2-hours work. The operation was repeated for the bridge pickup (pictured) but this time with the string side towards the faceplate.20180328 125517

The pickups were immersed in hot wax, 80% paraffin wax and 20% beeswax at 63 deg.C. for about 2-hours before removing and wiping clean with a rag. The magnets were then energised using two strong neodymium magnets, making sure to magnetise the two pickups in opposite polarities. Doing this in a vice has the downside of leaving it magnetised and causing metal filing to stick. Ah well! Note that the bobbins are quite full.
 

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