Custom Fender Jazzmaster. Shielding the body cavities – Installing a brass shielding tub, and plates

It’s good to be finally able to catch up on some of the jobs I’ve been setting aside, whilst I’ve had my dodgy vision sorted out. This refinished Jazzmaster body has been polished up and sitting around – just waiting to fit-out. I made a DIY brass shielding “tub”, out of thin brass sheet, as far back as January, and managed to carry out some of the more tactile tasks, like painting and polishing – but haven’t previously felt confident enough to begin to do some of the more fiddly stuff, like soldering.

The original vintage white paintwork on a Fender Squier J. Mascis Jazzmaster body has been rubbed back and oversprayed with a custom Candy Apple Red, consisting of translucent red nitro, over a shoreline gold nitro basecoat. I’ve been itching to move this one along for ages – now it’s finally time to begin to work on the on-body shielding, and grounding.

Installing a grounding wire – linking the tremolo plate to the central “star” grounding point

The first thing I need to do, is to drill a conduit hole for an additional grounding wire – running from the main control cavity, and through to the tremolo rout. It seems that on the original Fender Squier J. Mascis Jazzmaster, the tremolo was probably grounded via the strings, and relied on the metal-to-metal contact of the strings, at the tremolo and bridge. A physical grounding wire would be much more reliable. At the closest point between the two cavities, there’s just enough meat to angle a long aircraft drill bit across, and to drill a conduit through. It’s just about safe enough to “eyeball” the hole, and to drill straight though – but it’s a wise precaution to place a small, thin metal plate inside the tremolo rout first, where the bit will emerge – just to make sure the bit doesn’t pop out and begin to drill through the thin base, and out through the back of the guitar. A 50p piece does the job nicely.

Once the hole is drilled, a piece of black, cloth covered, “push-back” wire is stripped at either end, and threaded through the new hole. One end is pushed into the designated central “star” grounding point – previously established on the side of the control rout. Here, the securing screw of a lugged tab will provide a solid contact – linking this new wire to the original, existing grounding wire from one of the bridge thimbles. The stripped metal core of the new wire is left exposed as it runs towards the new conduit, and it is sandwiched between pieces of conductive, self-adhesive copper foil. This holds it firmly in place against the side of the control cavity and also provides a conductive connection for additional copper shielding, which will be installed later.

Tremolo grounding via the newly-drilled conduit

At the other end of the new grounding wire – within the tremolo rout – the end of the wire is stripped again, is run up the side of the cavity, and the end inserted deep within one of the tremolo screw holes. Once again – the exposed wire is sandwiched between pieces of conductive copper foil, and secured to the side of the cavity. The copper foil is shaped to drape over the edge of the cavity and around the screw hole, where it will provide direct metal to metal contact with the underside of the tremolo plate, once installed. Once the new ground wire is secure – it’s function is confirmed by checking conductivity with a multimeter.

Fender “62 Reissue” Jaguar/Jazzmaster Tremolo unit

I’ve sourced a Japanese made, Fender ’62 Reissue tremolo unit, (Fender parts number 026-4248-000) for the build. The unit is supplied without fixing screws, and without a tremolo arm – but I’ll probably be swapping the collet out for a Staytrem upgrade eventually, and I have six screws from a set of 12 to install the plate. They’re the same as used on most Fender tremolo units – including vintage-style Stratocasters, and are listed on Fender spec sheets as parts number 001-6170-000.

Fender “62 Reissue” Jaguar/Jazzmaster Tremolo unit – installed

The tremolo plate is installed without any problems. The pre-drilled screw holes are perfectly placed, and the screws tighten down to hold the plate securely. The arm collet is locked into place with the sliding lock button, so that it doesn’t flap around loose, before the guitar is strung.

Fender Jazzmaster – shielding the cavities

The Fender Jazzmaster utilises a few brass plates, together with a formed, brass “tub”, in order to provide an element of electromagnetic screening. On more modern versions, and notably on the more cut-price Squier versions – this is now replaced with a coating of black conductive paint, over all of the cutaway routs. The paint effectively creates an EM screening “Faraday cage” – and reproduces the same effect as produced by lining the cavities with strips of copper foil.

Fender Jazzmaster – shielding the cavities with conductive copper foil

The copper foil approach is the usual standard for all my builds. It’s simple, effective, and it helps to link together a contiguous “ground”, which combines and unifies the ground side of the pickup circuitry, together with the shielding effect of the screening. The shielding will help eliminate any troublesome “buzz” from the, notoriously sensitive, “pancake” coils of the Jazzmaster pickups. There is a certain school of thought which attributes a definite tonal effect on the pickups – especially on more vintage Jazzmasters – due to the use of thicker brass plates as shielding and, since I want to reproduce as much of the authentic tone of the Jazzmaster as possible, I’ll therefore be “doubling-up” on the shielding in this build – by installing the traditional plates, alongside a full lining of conductive copper foil. My typical “belt and braces” approach…

The internal cavities of the guitar body are fully lined with overlapping strips of heavy-duty, self-adhesive, conductive copper foil. Once the copper foil has been installed – the whole area is firmly burnished down with an agate burnishing tool.

Fender Jazzmaster shield plates

The set of shielding plates for a typical ’62 vintage Jazzmaster, consists of four main parts. Two separate plates which fit – one under each pickup, a flat plate which sits at the bottom of the rhythm circuit switch cavity, and a formed brass “tub” which sits inside the lower, main switch and control cavity. I’ve already made a DIY “tub” – formed from 0.1mm brass foil, and I had also formed a similar tub to fit the rhythm circuit cavity. However – on studying an original Fender spec sheet – it’s clear a flat plate was the actual approach used, and so I’ll cut my own plate out of some 0.25mm brass sheet. This seems to match the gauge of similar Jaguar and Jazzmaster plates.

Fender Jazzmaster, rhythm circuit, shield plate template

The two under-pickup plates, however, are genuine Fender original parts which I’ve managed to source from a UK supplier (2 x Fender parts number 005-4439-049). Unfortunately – all of the other shield parts only seem to be available from suppliers in the USA. Shipping and duty charges make their import way too expensive – hence my DIY “tub” and rhythm circuit plate approach. For the home-made plate – a Fender technical drawing, scaled to size and printed out on card, provides a traceable template which can then be trimmed so that it fits the base of the cavity.

DIY, Fender Jazzmaster, rhythm circuit shield plate

The template is placed on some 0.25mm thick brass plate, and the outline traced using a sharp stylus. The shape is relatively easily cut out with a pair of tin snips, and the sharp, cut edge is then de-burred with the shaft of a screwdriver.

Fender Jazzmaster, rhythm circuit shield plate installation

Fender used to use ordinary, triangular glazing brads to fix the shield plates into position – but even these are hard to track down, here in the UK. Where they are available, for use with old-school brad guns – they’re only available in bulk. However – I’ve managed to find a source who will split a few, spare strips of brads – (enough for a hundred-or-so Jaguars and Jazzmasters). Individual brads are peeled off the strip, and they push into the sides of the chamber with the blade of a screwdriver. A dollop of solder over each, helps keep everything in place.

The original schematic shows a ground lead running from one of the solder joints, up and onto the brass shield plate which sits under the neck pickup plate. This illustrates a necessity to physically link all of the separate brass shields. Although the copper foil will effectively do this job anyway, I’ll fit a linking lead, once I get the pickup shield plates fixed into position.

DIY, Fender Jazzmaster, control circuit shielding “tub”

It seems the under-pickup plates are physically connected to the main “tub”, probably by solder joints onto a couple of folded tabs. This will help hold everything in place, and stop the individual plates from moving about, and rattling. I’ve neglected to feature any such connections on my DIY “tub” – but it’s easy to form up a couple of suitable pices of brass, using spare cut from my unused rhythm circuit tub. The tabs are temporarily held in place with small strips of copper foil, and then (roughly) soldered secure. I drop a few extra spots of solder onto the exposed tabs, so I can physically connect the under-pickup plates once everything is “in-place” on the guitar.

Fender Jazzmaster, brass plate shielding

Once all of the shielding components are fitted into place – it’s easy to solder the pickup plates to the main tub, so that everything sits secure, and doesn’t move about. The fit of my DIY tub is a little bit wayward here and there – but I think it’ll do the job just fine. Now that the neck pickup plate is in place – I can install the short grounding lead between it, and the rhythm circuit base plate. A piece of the usual, black, cloth-covered “push-back” wire does the job.

The main tub fits tight enough within it’s rout, so that there’s no movement or rattling. The small lugged tab is screwed into the hole which connects at the central “star” grounding point, and this ensures the fit, and the conductive connection, is absolutely solid. The screw and lug additionally provide a physical, metal-to-metal connection – bringing together all of the conductive shielding parts, and offering a point to bring together subsequent ground wires. Continuity of the components laid thus far is confirmed, as usual, with a multimeter.

Fender Jazzmaster, under pickguard shielding plate

On vintage Jazzmasters – the enclosing, “Faraday cage” effect was completed, under the scratchplate, with the addition of an aluminium shield plate. A re-issue, USA made, Fender Jazzmaster Pickguard shield, (Fender parts number 005-4452-149), perfectly matches the screw hole configuration on this J. Mascis Jazzmaster body and, once fitted into position underneath the pickguard, will complete the shielding effect. It’s important that this, too, is contiguous and connected to the rest of the shielding elements – so a few extra tabs of conductive copper foil are run out onto the body, where they can create positive contact points. These are usually best placed around suitable screw holes – where the downward pressure of the screws and scratchplate can provide solid contact.

Fender Jazzmaster – Fitting the pickguard

The final touch is to install the chosen pickguard for the first time. As with most Fender offsets, it seems – there are plenty of different fitting options out there, (US, Japanese, re-issue, Vintage), and I’m not entirely sure where the J. Mascis Jazzmaster fits in. There are parts of it which seem to fit the metric standard – others which seem “American”. The excellent fit of the Fender vintage-style aluminium shield led me to belive a similar, vintage-style Fender pickguard would exactly match the screw hole placement. However – that didn’t work out. The Fender plate I obtained actually seemed slightly too small, all around. Instead – an “American ’62”, faux tortoiseshell scratchplate from Custom World Guitar parts in Amsterdam, fits perfectly and exactly follows the outside lines and contours of the body. (The bridge post holes are slightly offset – but everything will eventually be covered up, visually-speaking, once the bridge is in place). The scratchplate is fixed with 13 standard scratchplate screws – although I’ll swap them out for stainless steel screws, once I manage to get hold of another batch.

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