Custom Fender Jazzmaster. Shielding issues, and making my own brass “tubs”

It’s going to be a while before I can move my Jazzmaster build towards a dry assembly – but I can, at least, begin to take a look at the shielding elements.

Bridge grounding wire location

As with all electric guitars – the pickups tend to be much less noisy, (background hum), if the wiring, pots and switches are isolated within a kind of Farraday cage arrangement. This conducts electromagnetic interference around and away from the circuitry – sending it all directly to the ground side of the circuit. If a guitar isn’t properly shielded, not only do the pickups tend to be noisy – but all other outlying metal components can become “receivers” for EM interference, and when the player touches, for example, the bridge – the pickups can amplify the interference. The most troublesome background noise tends to come from everyday, domestic wiring circuits or fluorescent lighting ballasts, and vintage-type single coil pickups seem especially prone to interference. Wherever it comes from – it’s a pain, but it can be dealt with, relatively easily.

The easiest way to reduce electromagnetic interference, is to completely surround the wiring circuit with a conductive material. Practically – this usually means lining the body cavities with some kind of conductor, and then placing another conductive sheet over the top, to form a lid. For convenience and ease of access – this lid is normally placed directly underneath the pickguard, and hidden. Outlying metal components, like the bridge or tremolo plate can be connected directly into the shielding on the body cavities, so that all potential sources are eventually linked directly, and form a contiguous ground. The conductive liner to the cavities is, nowadays, most often made with conductive paint or thin adhesive copper foil – but in the early days of electric guitar design, attempts at shielding were often partial, and made by using thin sheets of brass.

1959 Jazzmaster shielding

This was especially the case on early Jaguars and Jazzmasters. On early Jaguars, shielding was added only to the bottom of each body cavity rout. A collection of thin brass plates was inserted, and soldered together with the help of short connecting wires. On the earlier Jazzmaster – the main control cavities were lined with formed, brass “tubs”, and these were soldered to a pair of flat brass plates, which sat underneath each pickup. On the Jazzmaster, the shield was completed with an aluminium cover plate, and this was die-cut to fully follow the shape of the pickguard. By the time the Jaguar came to market, full coverage had been engineered down to a smaller, rectangular cover plate, surrounding the immediate area around the pickups – but the outlying chromed metal cover plates served the same purpose, and so these were directly connected to the brass shield plates via small jumper wires.

In beginning the shielding work on my Jazzmaster build – I need to decide which method I’ll be using and, since this is a Fender/Squier body, also take stock of what measures are already “built-in”, and what might, additionally, be required. I’ll probably line the main cavities with copper foil, regardless. This has become a regular task on all of my builds, and it’s usually enough to render the wiring completely free of any outside interference. There is, however, a question of tonal benefit. Hotly debatable perhaps, but a detail which might theoretically have some bearing on my eventual process. The thing is – quite a few modifications were originally developed to help change and shape the output signal from early single-coil pickups. On the Jaguar, for example, the pickups were surrounded by chromed, ferrous claws – in an attempt to “focus” the pickup response. On Telecasters, the neck pickup is surrounded by a metal “lipstick” cover – again, supposedly, to help tame some of the single-coil’s chime-like response. On all single-coil pickups – if you lay them on top of a sheet of metal – you can subtly change their character. Many players cut a sheet of brass to sit under their Stratocaster or Telecaster bridge pickups – all to “beef-up” the pickup response. There’s some logic to the conclusion therefore, that in fitting traditional shielding plates, there’s a significant amount of metal being installed which might have some effect on the character of the sound produced. In replicating the shielding method, logic says I’ll be fitting it out to sound authentic.

Form my own Jazzmaster shielding “tub”?

So, as usual – it looks like I’ll be building the Jazzmaster with “belt and braces” in mind. I’ll line the cavities with brass foil and use a single “star” grounding point for the wiring – but I’ll also look to provide the traditional brass plates and tubs. Unfortunately however, there just aren’t any Fender original components to be had, on the market. Certainly not here, in the UK. It is possible to buy real, vintage components – but they’re madly expensive. Some new, genuine Fender parts are available if I ship them in from the USA – but for a $20 brass tub, I’m looking at $40 shipping, and then import taxes and VAT on top. I can buy 0.1mm, A4 sized brass foil sheets for a couple of quid. Now, my metalworking skills aren’t really up to much – but I’d be crazy not to try and attempt a spot of DIY.

After much searching – I manage to find some genuine Fender pickup plates from Custom Guitar World in Amsterdam. Even with the effects of Brexit – I can still get them here without too much outlay or delay. But for the tubs – I’m going to have to try and form them using some regular tools and materials I have kicking around the workshop. I figure it might involve hammering the thin metal over a former. It seems logical, therefore, to knock up a suitable former, first.

MDF former, shown in-situ

The control cavities on my Jazzmaster body are approximately 32mm deep. Two sheets of 18mm MDF, glued together, gives me a slightly deeper former than I need – but it should allow me to trim my metal sheet to size once formed, fold over the tops, and tidy up any sharp edges. I trace the required shape direct from the guitar body, and then cut it out using an electric fretsaw. The final shape is then smoothed and refined, using a drum sander attachment on my pillar drill. It’s a simple enough way to spend an hour-or-so in the workshop, and the end, the result fits the body cutout quite well.

Basic tub shape, formed from 0.1mm brass foil sheet

I probably should have taken more photographs – but the actual process wasn’t too far away from my original hunch. Suffice to say – there was a fair bit of hammering involved. I did wonder if it might be possible to use the former, and literally pound the foil sheet into shape using the guitar body as a mould – but I’m glad I didn’t attempt such a thing. In the end, I gradually pressed the sides down over the former until I had a rough, “draped” shape. A spot of hammering tightened up the angle transitions, with a little bit of folding at the corners. Then, once I’d trimmed off a few pieces of surplus, I was able to transfer the basic shape in to the cutout on the body, and begin to push and stretch it into a more precise shape, using a few burnishing tools. 0.1mm brass foil is thicker than those foil take-away trays you get – but it’s almost as easy to manipulate. (Just make sure you wear some gloves to avoid getting cut on those sharp edges).

Now, we can all laugh about this, but – I don’t think my end result is quite so far away from what Fender was originally producing in the late 1950’s. OK – their’s probably looked a little bit more “pressed”, and didn’t have that “Art and Crafts”, “takeaway tray”, hammered look – but mine fits where it touches, and by the time I’ve got it secured into place, with the pickup plates in place and the pickguard on – who’s to know the difference anyway? True – it’s a little slack in places – but further careful stretching and burnishing gradually firms up the whole construction. Although the brass foil is only 0.1mm thick – it’s a surprisingly sturdy structure once installed.

Tear repair with solder over copper tape

As I burnish the sides of the tub into shape, against the sides of the guitar cutout – I can also push the lower corners in, so the the fit is improved. Inevitably – where the shape goes in and out – there’s a risk of tearing, and one such tear occurs towards the wider end of the tub. I cut a few strips of adhesive copper foil, and patch them over the tear. A good dollop of solder, spread out, seals everything off nicely, and helps to preserve the overall rigidity.

The foil, has been trimmed to the height of the former, and the 4mm excess can be folded over at the top edges, so that the finished tub just lines the inside of the cutout. This further firms up the overall shape, and makes the finished tub much safer to handle. I’ll establish a few contact points to work with the cover plate, at a later date.

Eventually – the tub has a reasonably good fit all around. At the pickup openings – I’ll use the pre-formed Fender plates, and will solder them onto the formed tub. At the other side – I’ll make the smaller, simpler tub by following much the same process. That too will be soldered to attach to the pickup plates. The finished insert should be well-fitted and secure but – to counteract any often-reported rattling – I’ll probably look to install a few, well-placed screw attachments to the walls of the control routs.

Emerging bridge grounding wire becomes a central “star” grounding point

One such screw attachment will be ideally placed at the emergence of the pre-installed bridge grounding wire. The wire had been sheared off – presumably before the body was sold-on as a separate component. However, there was enough bare wire of a suffient gauge still left in the conduit, to tap into with a small scratchplate screw. This screw, with a lug attached, helps pull the tub into shape, and holds it firmly in place. The screw also connects well with the bridge grounding wire, and continuity is confirmed with a multimeter between the tub, lug, screw and nearby bridge thimble. There is no pre-installed grounding wire running to the tremolo cavity, and so I presume the grounding of the actual tremolo plate is supposed to be achieved through the direct metal-to-metal connection offered by the strings. I’ll drill another conduit instead, and run a grounding wire separately into the main control cavity, where it can connect into the overall shielding ground. My home-made tubs might just work!

Second rhythm circuit tub in progress

Update 29/01/2021
I repeated the process and formed up a second tub for the rhythm circuit rout. Much the same issues as before – but a bit of an easier shape to deal with overall. I still need to sort out the final fitting, and still need to solder in a couple of the corners to make it a bit more robust – but once I begin to put the Jazzmaster together, I should be able to join the two tubs onto the two brass pickup, cross-plates. Overall – the fit seems good, without any obvious movement, but I can always secure anything loose with strips of adhesive copper foil.

Home-made Jazzmaster shielding tubs – awaiting final fitting

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