> From:    The Bus Depot <vanagon@BUSDEPOT.COM>
> Date:    Mon, 16 Apr 2007 23:04:12 -0400
>
> Electronic keyboards are no better, since these are usually acoustic
> jams in the middle of a field with no electricity; wandering up with
> a cheesy Yamaha plastic keyboard with 4 inch speakers and D batteries
> just wouldn't cut it.

Get a guitar amp with a good speaker but thrashed electronics, or an old
stereo speaker.  Also get a two-channel car stereo amp (50 to 100 watts
or so) that has bridgeable outputs, and a couple of gel-cell batteries.
Put the amp and the batteries in the bottom of the cabinet and wire it
up.  Also wire the batteries to a connector on the outside of the
cabinet, so you can (Vanagon content) plug it into the van to recharge
while you're driving home.  If it's an old stereo speaker, mount a
handle to the top so you can schlep it around.  For a guitar amp or a
speaker, you could even put some lawnmower wheels on it if you're feeling
really lazy.  :)

Using the power of math, I will try to show that this isn't an insane
idea.  50 W is 4.2 A at 12 V; the amplifier won't be 100% efficient but
you could probably get 66%, making it draw about 6.3 A.  The keyboard
itself probably doesn't need much - maybe another 1 A @ 12 V, giving you
a total draw of 7.3 A.  A 12 V, 12 Ah (20h) gel-cell weighs about 8.8 lbs
(4 kg) and could give you 7.3 A for an hour before being completely dead.
This is an hour of tunes at 50 W continuous - in other words, turn the
volume up all the way, tape down the lowest key on the keyboard, and walk
off.  At less than full volume, and with not playing speed metal on the
piano, the average draw will probably be less, making the battery last
longer.

Matt Roberds