electrical safety for guitar builders

[John Morton]

I have provided piezoelectric transducers in a number of my instruments, which are all made from metal.  As a precaution I installed an insulating bushing to electrically isolate the jack from the body, without really knowing how or whether it matters if there is continuity between body, jack and tranducer.  My reasoning was that this is what happens in all electric guitars, whose bodies are made of an insulating material. 

But thinking it over, it now seems to me that the strings of an electric guitar are grounded, as is the shell of the cable and therefore the jack.  Bear in mind that I've never had anything to do with electric guitars.  However I use a Fishman piezo bridge on my archtop, and it hums badly if strings/tailpiece are not grounded to the shell of the jack.

I am working on adding a magnetic pickup to a guitar prototype, and feel I should start with a clear idea of where the potential difficulties or dangers lie.  Can anyone point me to a primer on now not to electrocute your customers?

thanks, John

[Joe Fox]

John,

Nice solution on the tailpiece.

And beautiful resonators.

On the res

If you are using a single pickup with volume control (with or without tone control)

You will ground the right lug of the volume pot.

The ground from the pickup goes to the back of the volume pot.

The ground to the output jack also goes to the back of the volume pot.

If you are using a Tone control just drop this parallel from the input of the volume control (left lug) There are a couple different ways to wire the tone pot.

The output of the volume control (middle lug) goes to the output jack.

Go ahead and make a good connection from the jack to the body.

You could just use the instrument body as the ground path.

But personally, I would wire the backs of the pots up just to make sure.

Let me know if you need me to sketch up how this goes for you.

[Paul Verticchio]

Hello Joe & welcome.

There's no arrogance inferred in any part of your response. It's good informative stuff.

"To respond to the question of the resistor and cap added to electric guitars for "safety".

The ratio of electric guitars with this mod to guitars without it is, I believe, somewhere around a gazillion to one."

I think it's even higher, maybe a hundred gazillion to 1.  I've never used this method myself.

One thing I forgot to mention in my posts is the significance of a high quality guitar cable.  I'm not talking a $200 Evidence Audio grade cable, but something MUCH better than your $10, 20' long Horizon cable. Personal note: avoid Monster cables like the plague.  Lava Cable is an excellent production cable as are Planet Waves.  My personal cables are made with Canare Star Quad cable using G&H 1/4" plugs and secured with high grade (read: NOT Radio Shack) solder.

A well engineered & constructed cable can eliminate certain noise issues.

Just 2 more of my cents (:

[John Morton]

That's all clear Joe, I'll keep that info for reference.  I'm eager to see how this turns out.  John