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

[Mark Pollock]

This is a nightmare for people who work with old amps, and all stage musicians that use amplification. I've had some lovely experiences with my lips getting shocked when I bump a microphone, and shudder when I recall a gig on an aluminum stage on a day that rained.

My solution is to use a wireless system, where ALL risk of shock from the guitar is simply eliminated. No risk of getting tangled, no risk of pulling an amp over, no risk of shock. Plenty of risk of interference, sadly, but it is worth it. I would never gig without a wireless. 

Sadly, you cannot account for the systems your customers choose to use, and cannot be certain to avoid electrocution if you ground the strings. . If you can avoid grounding the strings, then you avoid the problem of shock, but at a possible cost of hum. Again, a wireless system seems to eliminate hum as well, which actually comes from the ground connection.

[Russell Vance]

Just tell your customers to not put their fingers in power sockets and toasters.......this is not an issue that you need to deal with with 250 millivolts of transducer output and an earthed system.

If you wish to provide isolation from wrongly wired/ungrounded amps and stuff like that, that is another issue that I can deal with if you wish. Rusty.

[Thomas James]

John, your avatar is hilarious!

[Paul Verticchio]

Just run a ground wire from your tailpiece to the earthed (-) side of the jack,  add a capcitor & resistor (search for this info on the net) and it will stop all but 40v, and you will have your solution.

Best of luck.

[John Morton]

I would love to protect both myself and the poor blokes that play my guitars!  I will try and find out more about the wiring, and about how these issues are handled by builders in the world of amplified music.  Your comments are much appreciated.

Thomas, the art is courtesy of Robert Armstrong, who I presume did Frank Ford's also.

John

[John Morton]

Here is a good survey of safety for performers:

http://www.guitar-repairs.co.uk/electrical_safety_on_stage.htm

This article mentions the capacitor/resistor solution proposed by Paul V.:

http://www.guitarnuts.com/technical/electrical/safety/index.php

But the writer warns that there will likely be a significant increase in hum.

What looks best to me is an inline GFI breaker upstream of all your equipment.  (I have one of those for using power tools outdoors in wet weather.)  Unfortunately that is beyond the scope of what I can do to a guitar.

[Paul Verticchio]

Hello again John.

I wouldn't worry about this.  All you could do is pack an advisory narrative with your instruments.  You may want to check that with your attorney as perhaps remaining silent on the subject will more effectively minimize the probability of a liability claim if, in fact, any exists.

Here's the straight scoop from a guy that's been a working player for 47 years: Observing electrical safety precautions for guitarists is a lot like drunk driving.  Everybody knows what the "right thing to do" is and some obey those rules. Some unfortunately choose to willfully ignore them and at that point, their fate is in their own hands.

There are so many factors to consider that an effective defense, short of a municipal code inspection before every show, is impossible. 

If the guitarist is plugging into a full blown, professionally assembled & operated concert rig, the stage &/or sound company will have a properly routed, grounded and regulated AC system available. 

A pub or club, on the other hand, will have "some form of electricity".  Outdoor gigs that have drop cords running directly to power pole junctions can serve up anything from "nothing" to "all your gear just got fried".

Many guitarists also use vintage amps without 3 prong AC mains power cords or they cut the grounding lug off of a properly grounded plug. This is not good.  Also, over two dozen union electricians from various parts of the USA have told me that there's no real world uniformity on how a building may be wired.  Yes, there are codes and regulations but in practice they're often ignored or "worked around."

In summary, you'll have a better chance winning a game of "Whack-A-Mole" than you will trying to educate musicians on this VERY IMPORTANT issue. I've been reading articles about this same subject for over 35 years. I mean, it's been out there a loooooong time.

Heck, I have enough trouble trying to keep players from using instrument leads as speaker cables.

Let your satisfaction be rooted in making good guitars.

Best of luck,

Paul

[John Morton]

Thanks for your perspective on this, Paul.  My experience with real world electrical practices agrees with yours.  I will probably continue my practice of isolating the jack from the guitar, and run a connection with cap and resistor to the jack shell from somewhere on the guitar body.

John

[Joe Fox]

Hi,

I have not posted on here before, but, my main focus is electric guitars.

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.

To respond to the OP

You should realize that there is a distinct difference between ultra high impedance pickups like the crystal piezo, and magnetic pickups.

In an electric guitar made of wood like a Les Paul with stock humbuckers (passive magnetic) the pickups need to be grounded to the strings.

If you were to remove the stock humbuckers and install EMG active pickups you would have to remove the "bridge ground". Because the actives run through a pre-amp.

When you install piezo pickups on an acoustic guitar the strings are, of course, isolated from the pickup.

Now If you install a piezo in an all metal dobro for instance, you should  isolate the jack and pickup just as if it were a wood instrument.

That is of course if you are using the same product that you would use in said wood instrument.

(You should always consult manuf documentation)

Since piezos are ultra high impedence they run into a preamp and not straight into the the guitar amplifier, all this should be isolated from the strings and the metal instrument if you have one.

These are starting points, not absolutes, as there are myriad ways which guitars can be wired, and there are also a whole slew of wrong ways, and an almost infinite number of permutations of them all.

If you have specific questions, I can answer them for you.

If you are going to foray into electric guitar wiring, I would suggest you get the Schatten book.

I hope my first post doesn't appear TOO arrogant.

I acknowledge I have an issue with that.

[John Morton]

Thanks, Joe, it's not arrogant!

When you install piezo pickups on an acoustic guitar the strings are, of course, isolated from the pickup.

Interesting.  Note what I said in my original post about the Fishman bridge.  Do you mean to say there is something wrong with grounding it to the jack?  I'm pretty sure I was just following the manuf. doc sheet.  (It took some doing to wire the string ends - on that guitar they are held in a wood piece.)

But to return to the job at hand ... I'm talking about a pickup (probably single coil, passive magnetic) in a metal body guitar.  Grounding the p/u to the strings also grounds the body, through the tailpiece.  The question is whether to isolate the jack from the body.  I could also isolate the strings/tailpiece from the body if that had some purpose.

My apologies if I am not using terms correctly.  The Schatten book looks interesting, but may not address my situation specifically.

John

[Joe Fox]

"But to return to the job at hand ... I'm talking about a pickup (probably single coil, passive magnetic) in a metal body guitar.  Grounding the p/u to the strings also grounds the body, through the tailpiece.  The question is whether to isolate the jack from the body.  I could also isolate the strings/tailpiece from the body if that had some purpose."

No need to isolate the jack in the above situation.

If the guitar is grounded properly it would actually be impossible to isolate it electrically even if you did so physically.

A good understanding of grounding is key.

All oceans run to the sea and all grounds run to the jack and ultimately to the amp.

Therefore, when you ground the strings you ground the bridge, you the player, the metal body of the guitar.

Are you using a volume control on the metal guitar (dobro?)

Now, the Fishman......

This is why I said to follow the manuf instructions.

Fishman are often exceptions.

That particular product requires a bridge ground (string ground)

Since you have a wooden tailpiece that poses a problem.

How did you solve it?

[John Morton]

The Fishman - the wood part of the tailpiece has a row of string holes with counterbored recesses for the ball ends.  I cut a thin strip of stainless steel, 3/16" wide.  Then I pressed it into each recess in turn, until it took the zigzag shape in and out of the 6 sockets.  I worked it back out, punched a 1/16" hole for each string, soldered a ground lead to one end and shoved it back in to stay.  The wire sneaks down one side of the trapeze together with the bridge wire, very inconspicuous.  The jack is mounted externally next to the end pin, crosswise.

I do plan to install a volume control.

Grounding the body is really what I was hoping for, because it would be so easy to accidentally ground it anyway.

Not a Dobro!  These are based on the National design, see at www.jmorton.us if you're curious.

thanks again for your help

John