Tindrrel's JR-1M

[wokkaboy]

well you been working on the IB-6 haven't seen an update on this build for ages so assumed it was on the backburner

[stan]

nice to see this one Sam, looks good

[Tindrrel]

I'll post another update that will fill in the month since that previous photo. It's not done yet.

[wokkaboy]

good stuff Sam sounds like the build has progressed a fair bit since the last photo

[Tindrrel]

So, it's been a year of gathering decoration for the guitar. Then a couple of months putting a clear coat over the top.

Finally getting around to installing the hardware.

The bridge, nut, machine heads, strap pins are installed. Putting the pickups in I got to thinking about copper shielding.

I was told to be careful of the braid on the pickup leads - that if it touched the copper it would short the pickup.

This confused me, as I thought the braid would be the ground wire of the pickup, with the centre being the "hot".

In that case wouldn't it be desirable (or at least inconsequential) for the braid to touch the copper? As the copper and the braid would both be "ground"?


(You can see the braided leads, haven't put the copper in yet. The neoprene blocks are instead of springs to hold the P90s level with the screws holding their height.)

[Simon Barden]

Hi Sam, I'm new here since you last posted on this. The shielding won't short the pickups unless you've decided to reverse the polarity of one of the pickups, swapping the signal and ground connections for an out-of-phase both pup selected sound - when touching the shielding will ground one of them. If one of them is RPRW with respect to the other for a hum-cancelling mid position,
then the shield will still be ground on both pups.

Otherwise, you are correct, the braid is a ground, as should be any copper shielding. Even the pickup screws should be at a ground potential. In an ideal world, the pickup shield and the copper shielding wouldn't touch, as it's always best for there only to be a single path back to the main ground point. But with multiple ground paths in a very small distance of the common ground point, it normally doesn't make that much difference, though you might get a bit more noise than if the pickup lead had a plastic sheath and the ground paths were independent. If in any doubt, simply wrap some electrical insulating tape around the pickup cables where they may come into contact with the copper shielding.

P90s with their large flat coils are prone to picking up all the electrical noise going, so it's certainly wise to shield as much of the body cavities as possible.

[Tindrrel]

I lined the pickup routes and control cavity with copper tape. Got confused about the high resistance between the different sections until I realised the copper wire I'd used is enamel. Fixed that and got much more reasonable results.

Working on how a 2 x V, 2 x T, 3-way switch wiring diagram applies to the concentric pots I've got. Probably be over a week before I get time to do soldering though.

[Simon Barden]

Draw it all out and check it twice or more, before committing to the soldering. If you use paper and pen, you can still take a picture of it and post it here to be checked if you feel unsure.

[Tindrrel]

It's the same circuit I've used before. Just the first time I've had to go 3D on it with stacked pots.

[Simon Barden]

As long as you remember which is the outer control (the top pot) and which is the inner knob (the bottom pot), you should be fine. Presumably if one pot is audio taper and one is linear, then that decides which you are using for volume and which for tone?