Analogue-sequencer

> It's funny you would mention a 9v power supply - my P3 (1009) has 
> 9volts printed above its power jack - however, it came with a 
> 12v PSU, 
> and it won't boot when powered with a 9volt source!

I'd guess your 9 volt supply is the wrong polarity.
The power input on P3 feeds a voltage regulator that provides the internal 5
volt supply.
The regulator needs at least 7.5 volts input to guarantee a smooth 5 volts
output, but the supply can be anything from 7.5 to 15 volts.
I state 9 volts because that's enough margin for the regulator without being
excessive.
In theory the regulator can take up to 30 volts, but it would run really
hot.

Best regards,
Colin Fraser
Sequentix Music Systems Ltd
http://www.sequentix.com