Sequencer microprocessors

[Fraser, Colin J]

> -----Original Message-----
> From: Budweiser [FTS] [mailto:budweiser at ozemail.com.au]
> Sent: 14 January 1999 07:37
> To: synth-diy at mailhost.bpa.nl; Stewart Pye
> Subject: Re: Sequencer microprocessors
> 
> Thanks for the advice...midi control is something i will be 
> looking at,
> triggering
> first, and then control of all paramater (sound editing knobs 
> etc).This is
> where
> things can get quite complex, and discrete logic would mean a 
> huge PCB,
> bigger
> than the original 909!
> 
> I'm basically going to keep going until ive spent $1000 on 
> parts, and see
> just how
> far i can go with the actual clone of the 909, and then the 
> extra features..

The 808/909 clone I built cost me about 400ukp in parts (and probably 30% of
my spare time over a 2 year period).
That included a 4 unit rack case that cost 40ukp, and PSU components that
cost another 20ukp.

My unit only responds to midi triggers, and acts as a midi to cv convertor
too. The processor handling this is a 6502, and I have written a drum
pattern sequencer that runs on another 6502 machine that could easily be
ported to run on the internal processor of my drum unit - I would just need
to add a keyboard and display unit.
That would probably only add another 100ukp in parts at the most.
I chose to keep the sequencing separate for flexibility.

At the moment I use a TR626 for drum patterns. This feeds a BBC Micro (6502
based home computer) via midi, which passes the 626 data thru to the drum
module adding data from a pattern based 8 track sequencer on the BBC. It
also outputs din sync for my 303/606/202.
The next stage is to build a hardware pattern editing interface for the BBC
sequencer - probably 16 or 32 knobs and switches.
I'll also be adding cv/gate inputs to the BBC sequencer so it can record
patterns from my Pro-One or 303 internal sequencers.

You'd be insane to build a sequencer in discrete logic (unless you want an
analogue sequencer). 
With any 8-bit micro (80x1, z80, 6502...) you will be able to build a
sequencer will all the features of the 909 sequencer, but with the ability
to change between write and play on the fly.
The way I wrote my sequencer, there is no separate write / play mode. There
are separate keys for editing patterns and selecting patterns etc. so you
can always edit any pattern that is playing.

Midi control over the sound parameters in the 909 circuits will be quite a
job. Most of the pots will need to be replaced with OTAs, and you'll need to
provide all the pots for manual control with a scanning circuit to read
their values.
If I was going to do that, I would probably just build the knobs as a
general purpose controller unit so I could use it to edit other devices than
the drums.


Colin f