Super capacitors as a power supply

Has anyone experimented with using supper capacitors in place of a 9v batt in a pedal or acousitc guitar preamp?

What caps do you plan to use? How are you going to charge them up? How will you balance and monitor them? What will they cost? They can be expensive and complicated. I have a system that could do this, but it's for another use and likely costs more than a 9V battery, all the pedals on the board and the board itself.

I was actually going to do that to an entire instrument, so that a built-in preamp could be charged very quickly before a gig (I really hate 9V batteries). I never did, though I would still like to try it at some point. Getting the voltage step to work well (unless you plan on using multiple caps in series) is difficult. If you do anything with this though, please post about it. I find supercaps to be quite interesting.

Still working on it ....these links are interesting.

http://mi-si.com/products/
http://hackaday.com/2005/12/06/supercap-9v-battery/
http://www.popsci.com/diy/article/2008-02/make-instant-charge-screwdriver

Wow, I see it before me. Having these batteries on your pedal board, then plugging into a a wall socket 5 minutes before you go on stage, recharging in a couple of minutes and then ready to go, hum free for the whole gig.

I'm with Jack, it is interesting from a purely technical aspect, but practically speaking the concept is limited.

I can see some merits to on board electronics having their own rechargeable power supply. Or maybe if you were busking with a micro amp.

Otherwise most any place you are going to use pedals you are going to have access to line voltage (for your amp at a minimum.) And any capacitor powered device would likely still need a voltage regulator and associated circuitry.

So, why bother with the hassle and expense of an ultra large capacitor? Just use a 9v power supply unit plugged into the same line voltage as your amp.