Gold leafed Hardtail Stratocaster. Fitting the circuit wiring with 500k pots and a K40Y-9, 0.1µF PIO tone capacitor

Based on research from a previous post – I think the best way to approach wiring-up these Fender Vintage Noiseless pickups is to build on a standard, albeit slightly modified, Stratocaster circuit – and to treat the pickups a little bit like humbuckers. Humbuckers are normally matched with 500k pots, instead of the more traditional 250k pots on Stratocaster circuits. (Fender actually supply 1.0Meg tone pots for use with the pickups). Since reducing the value of the pots will slightly change the brightness of the tone, (lowering the value should brighten the sound), I want to compensate by using a darker, (higher value), tone capacitor. I then hope to experiment with a few treble bleed combinations in order to arrive at the ideal compromise – although I will probably try a modified “Kinman” R/C system first, based around a few recommendations I stumbled across on some forum or other. There’s a lot of “opinion” out there. Some of it helpful – but it always pays to check things out practically.

Gold hardtail Stratocaster – Circuit wiring components

So, the components I’ll be dealing with are:

2 x CTS Premium, 500k pots, short brass split-shaft, audio taper (2 x tone)
1 x RS Toneworks, 500k “Super Pot”, short brass split-shaft, special audio taper (volume)
1 x CRL 5-way, spring lever switch
Gavitt-style, pre-tinned, 22AWG cloth covered wire (black, and white (cream))
1 x “K40Y-9”, Vintage 0.1µF PIO capacitor
1 x Switchcraft, mono jack socket
1 x Fender, Aluminium shielding plate (Fender parts number 001-9640-049)

I also have some parts to make up an experimental treble bleed and tone shaping modification. I’ll be doing this separately, but will need to lay out my circuit wiring so that I can fit them in later:

1 x “Orange Drop” 0.001µF polyester film capacitor (for treble bleed)
1 x 220k ohm, 0.5w carbon composite resistor (for tone shaping / treble bleed)

I’m using a decent soldering station, capable of temperatures up to 480 degrees, and some ordinary fluxed solder. I’ve also got a small selection of shrink tubing – in different gauges and colours.

Stratocaster jack plug wiring – secure and snag free

The first job is to wire in the jack socket, and lay the ground and hot wires through to the main controls, and the central, “star” grounding point. I now follow a fairly standard procedure for wiring a Stratocaster jack socket. This involves isolating the solder joints with shrink tubing, and then forming the path of the wires, whilst the tubing is still cooling, so that they “fall” towards the wire conduit between the jack compartment and the main control cavity. In doing so – I can reduce the chance of the wires getting pushed around by inserting the jack plug. The shrink tubing also reduces the risk of accidental shorts to ground.

The jack socket assembly itself, forms a useful support to assist during soldering. Things are especially difficult with my dodgy vision – I really have trouble with my 3D perception – so even little tips like this can assist my technique, and get me through. It’s also a good idea to fix the plug socket part into the plate, before soldering up. To help keep the socket firmly in place, I use a castellated washer on the inside, and coat the inside of the retaining nut with a dab of Loctite 243, (blue) thread lock compound. This should resist the tendency for the plug to loosen over time which, in turn, can cause stress on the wiring and solder joints.

Having used two pieces of cloth covered wire to attach to the jack socket terminals – one white and one black, (white is “hot” – black is ground) – I cut the wires with plenty of extra length to spare, and twist the wires around each other, before threading them through the inter-connecting conduit. Once the wires are through – I can finally screw the jack plate down into place. (I’ve already previously insulated the back of the copper-shielded cavity, to prevent accidental shorts from the jack spring-clip mechanism). I can now better visualise the actual wire lengths required, and any excess pieces trimmed off now, will be used as patches and fly leads in the main circuit, later on. The black, ground wire needs to be long enough to reach the lug at the central grounding point. The white, “hot” wire needs to be long enough to allow easy attachment to the volume pot. There needs to be enough slack to allow the wires to be soldered-in to the main controls, whilst allowing the inverted scratchplate to be manoeuvered into position.

Stratocaster wiring with central “star” ground. “On board” components showing attachment leads

The black ground wire from the jack plug is attached to the grounding lug – together with another piece of black wire, which will act as a fly lead to connect to the circuit components on the scratchplate. The fly lead needs to be long enough to allow for connection to the back of the volume pot, as well as easy manipulation of the inverted scratchplate, into it’s final position. The ground wire from the jack, and the fly lead are soldered to the lug together, and the joint is protected with a small piece of shrink tubing.

In the image above – you can see the “star” lug in position. Once the screw is tightened down, the lug and it’s screw are directly connected to all of the other grounded components which are mounted on the body. The bridge and jack plate cover are connected via previously laid ground wires, and all of the internal surfaces are contiguous and connected, via the conductive copper foil lining. Once the ground jack wire is connected via the fly lead – all of the scratchplate mounted components will be directly connected to this common ground. Once the “hot” wire link is soldered to the wiper terminal on the volume pot – the circuit will be complete. It is one of the main advantages of using a common “star”, central grounding system like this – that the body and scratchplate can be assembled as two separate entities, and then quickly joined with just two solder joints. This allows for easy maintenance, and also the replacement of pickups and wiring – simply by mounting a new, loaded scratchplate.

Using a control shield as a support during soldering

Vintage Stratocasters often used a full aluminium shield underneath the scratchplate. This was supposed to help shield the internal components from EM interference – but the full plate has now largely been superceded by the direct attachment of thin aluminum foil to the back of the scratchplate. There is some supposed evidence which leads many to believe that the full aluminium plate may have had a modest effect on the sound produced by vintage Stratocasters – but the Noiseless pickups I’m using aren’t made the same way as classic vintage single-coils, and Fender seem to happily specify modern Stratocasters without the inclusion of full shielding plates.

Some Stratocasters do still use a smaller, cut down version of the shielding plate. The smaller plate covers just the control cutout – around the pots and switches. It’s main function seems to be to shield the main controls, and also to properly connect and ground, the pots and switch. Since it isn’t actually placed in the same general area as the pickups, it’s unlikely to have much effect on the sound – and other grounding precautions may also render it’s use, largely redundant. However, a small Fender aluminium cover plate, (Fender parts number 001-9640-049), does make the perfect template and support, to assist whilst wiring and soldering-up the basic circuit. I have an additional scrap piece of 30mm thick oak worktop, which acts as my soldering work bench. This has some holes drilled to accept some usual switch and pot configurations, and it allows me to position the work in a way which makes soldering that little bit easier. Once the components are “made-up” on the plate, the whole assembly can be quickly and easily transferred, and mounted on the scratchplate. Being able to solder up components away from the scratchplate, also vastly reduces the chances of damaging the plastic, by overheating, molten solder splashes, or by accidental contact with the soldering iron.

Checking the plate is in the right orientation, I attach the CRL switch, two CTS 500k pots and the RS Toneworks “SuperPot” – all in the required locations. The switch is installed with the spring facing away from the pots, and the pots are roughly positioned with the terminals of the two tone pots facing each other, as per the standard Stratocaster schematic. The components are held in place using the appropriate screws, nuts and washers – although they are only hand-tightened, and no locking compound is used at this stage. Whilst all of the lugs are easily accessible – it’s the perfect time to “tin” all of the terminals which will eventually be used. Once all of the contact points are lightly tinned with solder – using pre-tinned, cloth covered, “push-back” wire, makes the actual soldering of the circuit, much, much easier. Even for Mr Magoo’s like myself.

Stratocaster wiring – “Starting at the back”

Normally – I tend to start Stratocaster wiring jobs by laying grounding wires between the pots, and then by working from the switch, anti-clockwise round the tone pots, before finally returning to the volume pot. However, that K40Y-9 tone capacitor is an absolute monster. I’d like to mount that underneath the tone pot lugs – but even if I manage to squeeze it in there – I fear it might foul the sides of the control cavity. I quickly realise that I’ll have to turn the tone pots and mount them with the lugs facing away, “at angles”. Because of the tight space – I decide to wire the assembly in a slightly different order. I’ll have to work from “back to front”, and assemble components as they’re required to fill the space. When I get to the big tone cap – I may even have to temporarily remove the second tone pot, to allow for even easier access.

The first wire laid, is a length of white wire joing the two “control” terminals on the switch. The quickest, shortest join would pass over the top of the other switch terminals, and might get in the way later – so I prefer to lay the connection as a loop, which follows the rough shape of the actual swich. This routes it well out of the way of any moveable components, and also takes up as little room as possible between the switches and the pots.

The next wire laid – using black – joins the sides of the volume, and first tone pots. Quite often, I use a single length of uncovered, tinned copper wire to lay a running ground between all three pots. However – I’m short of tinned copper wire here, and it’s much easier, when working back to front, to use small lengths of cloth covered wire to do the same job. Since the “ground” terminal on the volume pot needs to be shorted back to the casing – I attach one end of the the wire through the ground lug, press the lug back to the casing with a pair of thin-nosed pliers, and then fix wire, lug and casing together at one point, with a single dollop of solder. The short ground wire is then cut to length – with enough slack to allow for a little rotational movement – and is then soldered to the side of the first tone pot. Once again, cloth “push-back”, pre-tinned wire makes cutting to length and soldering-up a relatively easy task.

Laying-in a K40Y-9, 0.1µF capacitor. A bit like getting an elephant into a bunk-bed.

This tone cap is huge, but I’m reliably infomed that the tone it provides will make up for everything. Nevertheless – I still have to find a way to fit it into the circuit. Next time – I may even consider using longer shaft pots to allow the cap to sit directly underneath the lugs. As it is – the best way I can find to mount the cap, is to lay it in front of the pot, and to run one connecting wire from the tone pot ground – via the capacitor – in front of, and slightly underneath the lugs – and then via the other connecting wire, to ground on the back of the tone pot. I was able to use the wires which came pre-attached to the capacitor, and roughly bend them to fit, but before soldering, I took the precaution of covering each with a length of yellow shrink tubing beforehand. That way – I hope to eliminate the possibility of any accidental short circuits, since it’s clear that everything will still probably have to move around a little – to get everything to fit.

Turning the first tone pot to accommodate the K40Y-9 PIO tone capacitor

With the capacitor in place – it’s clearly not going to be possible to set the pot terminals “face to face”, in the usual manner. I’m not even sure the cap will actually fit in the control opening in that orientation. The most logical configuration seems to be one with the first tone pot rotated roughly 90 degrees clockwise, with the second at approximately “11 o’clock” away from the usual. This lets the capacitor sit almost sideways within the control opening and, although one of the capacitor poles does come quite close to the unused lug on the second tone control – a little vertical separation is just enough to ensure that they never actually come into accidental contact with each other. Bending that unused lug back a little, helps too.

Linking the tone pots

Just before the capacitor connection to the tone “ground” lug is soldered, a second, short length of white wire is attached. The two wires can then be secured with one dollop of solder. The white wire is left slightly long, but once the pot positions have been finalised – the wire is trimmed to length and soldered to the centre, “wiper” lug of the second tone pot. Normally, one of the capacitor legs can be “run through” from one pot to the other. However, turning the capacitor the other way means this additional short wire is required, to do that same job.

Now that the relative pot locations are virtually finalised, a second black ground wire can also be laid between the sides of the two tone pots. Once again, a little slack is left for adjustment. This completes the “running ground” between all three pots.

Stratocaster wiring – connecting the switch to the pots

Once the two, outside “control” lugs on the switch are linked – and looking at the switch as in the photo above – the remaining three tabs on each side of the switch can be read:

Spring side – (control), neck, middle, bridge
Pot side – neck, middle, bridge, (control)

The Fender diagram which came with the Noiseless pickups is clearly wrong. From what I hear – this isn’t necessarily as surprising as it might, at first, seem. The neck and middle pickups appear to be sent to the wrong tone pots. Also – the bridge is left without any tone adjustment at all. Whilst this might be considered “traditional” – it does nothing to allow for any tonal control of the “humbucking” bridge pickup. Since there’s a reported tendency towards shrillness, and dreaded “icepick” tones – I want to redesign the switching functions differently, and give myself the ability to dial the bridge pickup back a bit.

To wire the switch in to the pots – four wires have to be laid. Three concern the tone pots. One, the volume pot. The first connection to be made – is a link between the “neck” and “middle” lugs, on the pot side of the switch. This effectively links the neck and middle pickups to share one tone pot. With this solution, the neck and middle pickups share one tone pot, and the bridge pickup can have it’s own, dedicated pot. The linking wire need only be very short but, once again, I prefer to use a slightly longer length which loops down alongside the vertical face of the switch. Functionally – the connection need only be a short length of jumper wire, but that might prove fiddly to remove, once all the other connections are in. By laying a tidier loop – the tight space is utilised better, and later modifications, if required, can be made much more easily.

The pot-side, neck terminal, (and with it the jumpered middle terminal), can now be linked to the first tone control, (the one in the middle – and closest to the volume pot). This is achieved via a piece of white wire, which is laid-in to connect to the middle, “wiper” terminal of the tone pot. It’s good practice to try and make all terminal connections at the switch travel downwards – so that all of the solder connections are made with the short wire ends passing up, through the terminal lugs. This keeps things tidy, makes for easier soldering, and also helps lay the wires in a manner which uses the available space economically. There are still, many more wires to fit in yet.

Once the neck, (and middle) pickups are linked – and the wire is soldered in – another length is laid, and soldered in place. This one, (another white wire), links the pot-side, bridge terminal with the “ground” terminal on the second control. (Actually – the “ground” input here acts as the “input” terminal. The circular, variable resistor just works in reverse. It’s just a naming convention thing. To me, if you’re looking at the three tabs below the main body of the pot, and looking from the back – the “ground” terminal is always the one on the right).

With both of the switch-to-tone-pot connections, it’s wise to loop and lay the wires as economically as possible. This makes later work easier, and allows for potential adjustments and re-alignment. You want to be able to move things about if you need to, and also to get in to fix unexpected issues like bad solder joints or dead components.

The final wire from the switch to the pots, actually links the volume pot to the pot-side control tab. There’s already a connection here, and so a second pre-tinned wire can usually be pushed through and secured, if the existing solder joint is heated first. The wire needs to join the nearby volume pot at the “input” terminal but, since a treble bleed system will be added later – it’s preferable to just trim the wire to length, and to leave it unsoldered at the volume pot, for now. Like all other connections – a little slack is left for adjustment, and the route of the wire passes down the switch, across the base plate, and then up – rather than following a direct, point-to-point, route.

Stratocaster control circuit. Attachment to the scratchplate, and wiring-in the pickups

Since I might have to do a little experimentation with the treble bleed, and with it, some chopping and changing – I’ll leave that for later. So now I can fit the circuit assembly to the scratchpate. This will allow me to double-check the fit within the cutout rout, and also let me wire the pickups in properly. With the pots and switch attached to the shielding plate – it’s an easy job to remove the fixings, whilst keeping the whole wired assembly in one piece. The plate fits the Fender scratchplate perfectly, and the nuts and screws are replaced to make everything secure. However – I’ll still not finalise the fix with Loctite, just yet. Not until I’m absolutely sure everything fits and works properly.

One change I can make, is to switch out the flat head, stainless steel switch screws I’d previously selected – for a pair of screws with countersunk heads. These will fit the pre-drilled countersinks on the scratchplate much better, and leave the screw heads flatter to the plate.

I’ve already fitted the pickups to the scratchplate – so once the controls are fitted , I can split out the “hot” and “ground” wires from the bundles I’ve already routed, and partially separated with shrink tubing. With the grounding wires bundled and routed towards the volume pot, a separate piece of shrink tubing keeps them compact, and pointing in the right direction. The black ground wires from the pickups are then trimmed back, the ends stripped, twisted together, and tinned. Finally – they’re all soldered to the back of the volume pot together. Although the ends are lightly twisted together – the individual wires are still, essentially, separate. It’s most logical to solder them close to where the volume grounding lug is pushed back onto the casing. A big generous dollop of solder here, brings all of the grounds on the back of the volume pot, together at one solder point.

The “hot” wires now remain, and they can be partially bundled, secured with shrink tubing and directed, so that they run along the length of the back of the bridge pickup – and on, towards the control switch. Before wrapping them – it helps to identify the “hot” from the neck pickup. The “hot” wires from both the neck and middle pickups are the same colour, (white). (The bridge pickup hot wire is yellow, and easily identified).

Stratocaster wiring circuit. Connecting up the pickups

Sometimes, I prefer to route the pickup wires around the right hand side of the switch – but I find that sometimes leads to the wires getting trimmed a little bit too short. I like to leave a little extra length, and that extra wire has to find somewhere to go. Wheras all of the wires thus far, are laid so that they run down the switch and away – I want to solder the pickup wires in “over the top”. By doing this – I can cut the wires a little bit longer, and run them around the switch and loop them away from the central space between the switch and the volume pot. This keeps the pot-side switch connections accessible, and should also leave me plenty of room to fit my treble bleed, and to hook-up the two connecting wires from the guitar body.

Whilst test fitting the scratchplate to the body, and looking for the most economical route for the pickup wires – it became obvious that the two, switch-to-tone-pot leads needed to run over the tone cap – rather than around it. Having left enough slack in the wiring, this was an easy adjustment to make, and it removes a potential pinch-point against the sides of the control cavity once the plate is installed. The end result might lack in some of the Spartan economy, of the kind commonly seen on cheaper, commercially produced guitars – but it works functionally, looks tidy, and functionally – I can easily get to individual solder joints, if I ever need to. Admittedly – that tone cap does make things a little bit difficult, and if I ever do need to change that out, I may have to disassemble some other bits of the circuit around it. However – with the wires now passing over the top, rather than around – I’m hoping I’ll just be able to desolder it, and slide it out backwards.

Now – I just need to come up with a working solution for a treble bleed circuit. Hopefully, one which will work well with the pickups and controls, and which will fit into the space I’ve purposefully left for it.

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