Analogue-sequencer

> A couple of questions:
> 
> How well secured would the expansion board be? (Digital instrument  
> history is littered with examples of unreliable daughterboards and  
> connections coming loose, the D-50 MEX being a prime example.)

I use turned pin PCB headers in turned pin PCB sockets.
They are hard to get in, and hard to get out.
DIYed P3s with cheaper sockets may not grip as hard.
 
> With the board in place, will the P3 boot up and operate with the V3  
> software at all (with the old bank structure), or does it 
> make the V4  
> jump permanent?

The v3 OS could be patched to run with memory board without opening up the
expanded space.
The memory expansion decodes a single address (top byte of the bottom 32k of
RAM) to a page select register, which selects one of sixteen pages of 32k
RAM.
So long as the page select register is forced to a fixed value at every
boot, and the pattern byte that would normally be stored there is held
somewhere else, v3 would run happily with the board in place.
 
> (I'm still on V3, and need to figure out a non-Windows way to decant  
> my V3 banks to V4 before upgrading.)

If you have v3 dumps in .syx format, I could run a few through the
conversion utility.
Unless I get fifty people all asking me to do a dozen dumps each...

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