X. Safety Considerations
We've all read posts on usenet new groups where someone has heard about someone else who rattled loose their fillings by using a talkbox that was played at excessive volume levels. The author hasn't personally experienced this, nor does he know of anyone who has. If the level of the amp is so high that tremendous sound pressure is being forced into the user's mouth, creating unwanted vibrations, then turn it down a notch or two.
A more realistic hazard is that the user will fry the amplifier by playing at excessive volume levels into the talkbox. The reason is that high frequency drivers are not designed to handle bass frequencies. They handle upper mid and treble frequencies, and reproduce those sounds very efficiently. As such, the drivers don't need to be rated at hundreds of watts. The average driver is rated at somewhere between 30 and 60 watts. JBL, Altec, and other companies manufacture drivers up to 200 watts each, but these are very expensive and are not found in any commercial talkbox product.
So pay attention to the wattage rating of the talkbox you are using. If it is identified as being able to handle 50 wats RMS and you use a 100 watt Marshall, then your talkbox won't sustain high volume playing for more than a few moments before it overheats, fries, then takes the amp along with it. An amp playing at full volume through a shorted speaker load is essentially playing through a short circuit. The output transformer and output tubes will attempt to soak up the power, they'll overheat quickly, and your amplifier will be history. Watch the volume levels through the talkbox!
Another caveat is the shock hazard that exists any time you use a PA system while playing guitar. Differences in ground voltages (ground potential) can produce nasty, though seldom lethal, shocks. Why does this happen? Your guitar is grounded to reduce hum that is picked up by the electronics in your instrument. A wire runs from the control cavity of your guitar to the bridge. your strings run across the bridge. The shield side of the jack on your guitar carries the ground signal along the guitar cable to your guitar amp. The ground signal is then dispersed via the amp chassis, through the amp power cable, to the ground circuit of the AC mains where the amp is plugged in. (Man! That explanation really puts the "electric" in electric guitar!)
The bottom line is that your hands are in constant contact electricity (hopefully a very minor amount).The author has been burned on the lips on more than one occasion when using a talkbox with a house PA system. Fortunately, there are several things you can do to minimize this threat: