TENS experience, anal too
Electro, like much in the BDSM world, is an acquired taste and one's initial tolerances become laughably low in retrospect. FIrst of all, don't make your own, don't use stereo output wires and an amplifier. Use a professional unit. The drug-store variety is junk; a real one should cost about 100 and up. High end (as from PES with all the attachments available) much more.
The TENS box can vary power, pulse and speed. To use a slapping analogy, you can smack soft or hard and rapidly or slowly. The "waveform" control does some interesting things.
You can also get conductive tape or rig up say, wire hanger wire up the sides of a butt plug or dildo. If you insert that, it will be even more fun than the ballsac routine. The sensations start as a light tingle, can get stronger, simulating internal massage and up to a deep internal PUNCHING you won't be able to endure unless you're locked in place. Good stuff!
I hope this is helpful. There is a ton of good electro info out there if you google it.
Also, don't forget to see my other post about the Ball Destruction videos we made. They're still up and I hope you can view them.
Page