Slightly different situation but similar results for me. When I had my 17" Powerbook, I would connect it to my TV with the S-Video cable to watch DVDs. When it was connected, I could feel a constant mild electric current when I touched any part of the metal case of the Powerbook. Not painful but noticeable.
that is likely because you are using a Japanese guitar or Mexican guitar. They have twice the voltage over there and that is translating to extra power on U.S. 110VAC, or the Mexican factory had their power hooked up backwards, and it has flawed the wood veneer so you are getting -110VAC. ...uh, seriously...
I find that a lot of amplifiers, especially if vintage or of vintage design, are very poor at earthing the signals. I have a silvertone tube amplifier that seems like it transmits a portion of the AC voltage through the instrument line in from one of its primary transformers.
If because of the equipment that you are using you simply cannot earth ground everything, and even if you do, the source of the voltage is in fact dirty leakage from a piece of equipment, I would highly suggest that you transformer a few key connections. use a jensen transformer (or other high quality transformer) between you computer and your sound gear. because you are using a MOTU that is likely hooked up via Firewire to your computer, you should place the transformer between you amplifier(s) and the MOTU. what this does is electrically isolates your computer rig from your equipment. to protect yourself, you could also place a transformer between your guitar and your amp. you might have to use a separate line driver (preamp) first, as i'm not sure you can or would be pleased with the results of transformering an instrument level feed, would likely have to be line level before it works well.
the TV situation might be different... do you have cable service? see if this stops when you disconnect the cable feed from your box. it is quite common for the cable companies to have an unusually high DC offset from their incoming lines, or a small AC potential on the shield. this happens, even if you aren't watching the cable box, just the fact that it is connected electrically to the system, which is in turn connected to the tv, in turn to the computer, etc...
if this is true, you can buy a DC block, but cheap ones mess up with the digital portion or "interactive" communication of digital boxes. again, jensen makes some nice transformers that address DC offset from digital cable lines too.
Jord is 120% right..It could B leathal..I heard about at least one guy buying the farm this way...I cannot recall exactly what happened...But I would ASAP Repeat ASAP go to the dealership and state the problem..They'll know and they'll fix it...It is VERY dangerous...Dont fool around with it...I aint kidding..........................!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !
When I am holding my electric guitar
when it is plugged into my guitar amp, and I attempt
to touch my computer (to start recording, for
example) I get an intense static shock.
There may be no solution. It could simply be your electrifying personality. But, barring that....
A static shock is less indicative of a poor electrical grounding scheme than if you had, as others have described, a constant noticable current when you touched the Macbook.
As you strum your guitar, you and your rig are building up a static charge which likely has nowhere to go because your amps input scheme doesn't tie your instrument cable shield to earth ground. Even if it did, you and the strings may not be connected to it, so the amps grounding may have nothing to do with it. You may notice it more when you're plugged into the amp because that's when you're "strumming".
Strumming your guitar and then touching the Mac is analogous to shuffling your stocking feet on the carpet and touching a metal doorknob.
This is less hazardous to you than it is to your computer and its data. But there is a solution. Check these out:
Something for the table:
Something for the floor:
You can get a mat for the floor that you simply step on before touching the Mac, or you can put a mat on the table and touch it before you touch the Mac. Setting your Mac right on it wouldn't hurt either. The mats provide a resistive path to ground that slowly and safely discharges the static charge. So, no more shock.
Regardless of what you do, be sure you have a good ground available and that everything grounds to the same place. Hopefully that's 2 copper rods driven into the ground somewhere outside your studio.
Many products, probably your Mac too, do not have a grounded case. This isn't a bad thing. But, like the doorknob, they can still have enough of their own ground potential to discharge a static charge.
Good luck Sparky.
Shocks suck. It is most likely (and please don't be offended) poor wiring on your guitar, OR you have a ground fault in your house wiring where you're plugged in.
I don't care where you're recording, even on the road, you need to have proper grounding for all your electrical. Go get yourself one of these puppies, and it will let you know if there is a problem with your ground, but also protect YOU and your equipment at a very reasonable price. If you don't go much on the road, get a model higher that has more features and filters.