Analogue-sequencer

>> I've posted a new picture of the completed main board -
>> see http://www.colinfraser.com/p3/p3-inside.htm
>
> looks nice...
> I guess you've taken MIDI off board to allow for mounting sockets
> anywhere?

Yes. With the sockets mounted on the board, there was no option to 
have them facing backward/forward in a rack mounted unit. I'll 
probably do an extra little board to take 3 PCB mounting DIN sockets, 
so there's a choice of whether to use chassis mounting sockets or not.

>> The key switches will need to have the right pin locations and
>> sizes, so it may be better if I were to supply the switches I used
>> with the board.
>
> Do you have a make/partnumber?
> this way I can check to see if the ones I plan to use will fit..

The switches I used are from Maplin.
Go to http://www.maplin.co.uk and look at part nos. DM76H (switch) and
DM77J (top). In 100's they cost 68p per step.

> I plan to use tact switchs (MEC 3FTL6's infact) datasheet here ;-

The test boards take only the Maplin switches.
But since tact switches are industry standard, multi-sourced, much 
more widely available, and cheaper, I'll make the PCB accept either 
the Maplin ones, or standard tacts.
Or if I'm happy myself with the label-able tact keytops, maybe I'll 
just make the boards tact only.

Cheers,
Colin f