actually if i had the $$ to spend at radio shack - i don't think the puck could easily be variable volt w/ a 4 position switch - could easily do off,3v 4.5v and 6v - use a TI or 2 and a rotary multi point switch and u could do several in between as well. - just ideas i've had. since when i looked at it it looks like there was lots of free space to put in more controls and other fun things 