Solid State Guitar Amp Forum | DIY Guitar Amplifiers

I've often wondered why the main switch on my Yamaha SS amp is 3 position. There's "On" [up], "off" [middle], and "On" [down]

I was looking around for answers, and found some discussion of this feature of the amp on HarmonyCentral, where the poster speculated that it was designed to give you a way to choose from an "On" setting that has less hum. I guess that could be true, but if you look at the actual circuit, I don't see any difference in the wiring that would enable that (and it's worth pointing out that, unlike some of my amps, the Yama is hum-free regardless of switch position).

Am I missing something? Why not just put a 2-position switch there?  ???

Well, some older amps use a switchable grounding capacitor so in some cases the switching circuit could be related to one. Here's an interesting article about them: http://psg.com/~dlamkins/Articles/ground-switch-death-cap.php?cat=amps

If no such circuitry is involved then I don't know either why to use a three position switch, maybe they were cheaper at the time. Some people say a switch like that is easier to switch on/off but at least I think it's not. Getting the switch to center position seems always more difficult than to just flip it to right direction. And another point, switch with center position off is easier to switch on accidentally.

Thanks. Great article. Makes you want to play acoustic guitar (with nylon strings)!  xP