Help! Wiring did not work

I just wired up my ST-1 build, plugged in and... nothing.

My ST-1 kit came with three wires to solder in: all of them attached to the volume (not two attached to the tone as per the PitBull wiring diagram - see attached image#1).

Attachment 43222

The wire attached to the lug is yellow, and the two wires attached to the top of the volume are both black.

Following the wiring diagram (and various YouTube videos), I see that the yellow wire is the "'hot' wire to tip" and the two back wires are both earths. Accordingly, I wired the yellow "hot" wire to the tip on the input and one of the black wires to the earth lug (see attached image #2).

Attachment 43224

In accordance with this advice (see attached image #3)
Attachment 43223

Then I soldered the other black wire to the bridge.

I double checked the wiring. I re-soldered the wires to check there was a good contact. Every time I opened up the jack cavity the wires were still attached.

I'm out of ideas. Any help appreciated
Martin

It’s normally because you’ve got a signal contact touching the grounded shielding. Don’t fit the jack plate to the guitar but plug in a lead and see if you get any sound. Or it may be something in the main control cavity. There’s not a lot of a gap between the selector switch and the bottom of the cavity. Always a good idea to put some insulating tape on the shielding in areas where there may be contact with signal wire connections.

It’s actually not that easy to get a Strat jack socket fixed in place with everything working. Especially if the body is a bit thinner than a USA one (as many Squiers and Asian-made Strat-style guitars are. Even on US guitars it’s not easy, and I’ve probably wired over 50 Strat sockets in my time. It’s the one piece of the design of the Strat that I think Leo didn’t do very well. The jack plate needs to be a bit longer with the socket at a shallower angle to the top.

Thanks for that Simon - really clear.

I tried plugging in with the jack plate hanging off and... it works! I'll play about with some insulating tape and see if I can get it to work screwed in.

Cheers
Martin

It's normally something simple, and it's happened to me in the past.

Glad it's nothing major.

Good to see Simon got you on the right track.

FWIW, I typically don't put any shielding tape in the jack cavities of strats or teles. IMO the benefit is negligible and the chance of having a short are increased. I'll also point out that applying the copper tape to the metal jack plate is unnecessary as the plate itself is conductive.

There are alternative ways of dealing with an unshielded jack cavity, such as using coaxial cable as the output leads from the pots/switch to the jack, or twisting the positive and negative wire together in a helix fashion then applying heat shrink tubing over the pair (literally creating a twisted pair).

It worked. At first it kept shorting out when I pushed the jack plate into position. Then I realised the tip of the lead was touching the copper shielding tape at the back of the cavity (I put some insulation tape at the back and this solved the problem.

So, I see your point McCreed about not shielding the jack cavity. I also see your point about not shielding the underside of the jack plate. I didn't really think about this, but as it's painted black I guess it might be insulated (a little?).

I don't really get your comment about alternative ways to deal with an unshielded jack cavity - but I don't have because it all works now! Very happy.
Martin

If it's black hardware, then copper tape is the right thing to do on the jack plate.

Twisting the wires together makes thins neat within the main control cavity, but makes very little difference on an unbalanced signal cable. And by the time the wires come out into the jack cavity on a Strat, you'll want them separated anyway to get to the two jack tabs to solder.

Twisted wires are great if you are using a balanced signal with differential inputs (as on an XLR mic input on a mixer or an audio interface), but does very little for unbalanced signals. There is the argument that by twisting, the ground wire will pick up some of the RFI because it will sometimes be in front of the signal wire and absorb the noise, but it's almost negligible. I ran this through Hugh Robjohns from Sound on Sound magazine (and an ex-technical department instructor at the BBC) and he said it wouldn't do anything.

A shielded cable is more effective, but with standard single coil pickups, the amount of hum picked up by a few cm of wire mostly running inside a shielded cavity is negligible to the amount picked up by the many hundreds of feet of mainly exposed wire in the pickup itself.

I've shielded jack cavities on Strats before, mainly for completeness than any expectation it will do anything, but I always add insulation tape over the top at any point where the jack could touch. Remember that when the jack plug is inserted, it will push the tip contact out and down further towards the base of the cavity., so what might be OK without a jack inserted, can often become an issue once it is.

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So, I see your point McCreed about not shielding the jack cavity. I also see your point about not shielding the underside of the jack plate. I didn't really think about this, but as it's painted black I guess it might be insulated (a little?).

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Ah yes, I didn't notice it was black hardware, so good call on your part!

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Twisted wires are great if you are using a balanced signal with differential inputs (as on an XLR mic input on a mixer or an audio interface), but does very little for unbalanced signals. There is the argument that by twisting, the ground wire will pick up some of the RFI because it will sometimes be in front of the signal wire and absorb the noise, but it's almost negligible. I ran this through Hugh Robjohns from Sound on Sound magazine (and an ex-technical department instructor at the BBC) and he said it wouldn't do anything.

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I don't have the technical knowledge to dispute or defend that. I only know that it was information given to me by someone I respect and does have the technical know-how. I know this is next comment is a slippery slope, but I have also read lots of posts in other forums that say it works or at least helps, even with an unbalanced signal. However I understand "reading it on the internet does not make it true".

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I've shielded jack cavities on Strats before, mainly for completeness than any expectation it will do anything, but I always add insulation tape over the top at any point where the jack could touch. Remember that when the jack plug is inserted, it will push the tip contact out and down further towards the base of the cavity., so what might be OK without a jack inserted, can often become an issue once it is.

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With strats I always position the jack in the plate so the long positive contact is facing the front/top of the guitar so it can't be pressed against any part of the cavity (shielded or not). I also use a lock washer (antivibration) and ensure it's good and tight so it won't rotate.

I've had problems with the tip connector on Switchcraft jack sockets in both the up and down positions. It definitely won't go sideways, so you need to pick up or down. Sometimes 'up' will move the end of the tip connection against the end of the rout, so that you can't insert a jack properly. And sometimes down' will touch the floor of the cavity. A lot depends on the routing of the cavity, and the positioning of the screw holes for the plate. Pure Tone jack sockets make it so much easier with their much shorter tip contacts.

I feel that twisting wires will give some improvement to noise pickup, but not much. The idea of the twist on a balanced differential input arrangement is that both wires pick up equal amounts of noise - especially so when close to the source of noise when the noise wavefront is still spherical and the noise amplitude can vary significantly over a short distance. The tighter the twist, the better the noise matching will be, and the better the noise rejection will be.

On an unbalanced input arrangement, any noise reduction can only be by the ground wire being between the signal wire and the noise source and absorbing the noise signal before it hits the signal wire. At best, you've got a theoretical 50% coverage, which would result in a maximum 6dB drop in the level of noise picked up by that section of wire (which may be insignificant in comparison to the noise passed on by a single coil pickup). But if you say that vintage push-back wire has a core that's about the same diameter of the thickness of the cloth covering, then the actual amount of signal wire protected by the ground wire becomes a lot less, and really only where the wires cross. So the level of reduction bay only be 1 or 2dB. All worth having, but it's never going to keep the guitar quiet in a noisy environment. At worst, it won't do any harm, so you might as well do it.

It's the 'differential input' that does most of the noise reduction work with a balanced differential input. The 'balanced' part of that indicated that both the signal wires are at the same (high) resistance to ground, which primarily stops the risk of ground loops that can occur on unbalanced systems where one of the wires is tied to system ground. Any ground loop on a balanced system can be removed by breaking the shield connection at one end.

But balanced also allows one signal wire to be sent as one positive and one negative signal with respect to each other. Any the noise signal picked up by both wires is the same polarity, instead of opposite. Fed into a differential input (which sums the difference between the two signals), the original signal amplitude is doubled, whilst the noise signal nearly all cancels out.

So you need both a balanced system and a differential input for a twisted pair to work properly.

The EMI noise rejection/reduction is normally between 70-90dB with a balanced differential system and a tight twisted cable, which is why simply twisting the wires together for somewhere between 1-6dB of noise reduction is never going to compete. Using screened cable is far more effective than just twisting the wires together..

Twisting wires together certainly significantly reduces any outgoing noise. As the current flowing in each wire is equal and opposite, so will the magnetic/electrical field they generate be equal and opposite. Twisting the wires gets them as close as possible, so that most of the two fields generated cancel out, with minimal residual noise emanating from the pair. It's why heater wires in valve amps are twisted together. It may be a low voltage - typically 6.3v a.c. but it's a high current, and it's current that generates the noise fields. Without doing this, a lot of 50/60hz hum can be transmitted to the amp circuitry.