[sdiy] Chinese MG-1s??!?

[ASSI]

On Mittwoch 30 April 2008, Tom Corbitt wrote:
> Looking at the design, the only gotcha I see is the 4 TOG chips,
> which brings up a question I've seen asked over and over again on the
> list archives.
>
> What's the best way to recreate a TOG?

GAL/CPLD/FPGA, depending on inclination and purpose; i.e. do you want to 
replace existing chips or just implement something "along the lines of 
whatever".  Depending on the size of the chip you might even get all 
four TOG into the same package if you want to.  While microprocessors 
can do this when they are fast enough, the cheap ones aren't really 
made to provide a bunch of phase-locked signals from a single clock.  
Since that isn't really a desirable property for a musical instrument, 
this could actually be advantageous, but I'd still rather use real 
logic to losen up the phases.

Something like this would be helpful if you don't want to deal with SMD 
parts, however the CPLD are also still available PLCC packages (more 
expensive, then):
http://www.digilentinc.com/Products/Detail.cfm?Prod=CMOD

The TOG don't always have simple squarewaves as their output, see:

http://www.organservice.com/crm/topdividers.htm

A complete TOG needs a rather large CPLD and if you want to do something 
about the phase locking I'd go straight to an FPGA with enough pins to 
produce all note outputs simultaneously.  There is enough extra logic 
left to do things like breaking up the phase-lock, varying ouput 
pulsewidth, providing vibrato and different tunings.

The divider chips in the MG-1 seem to be simply 6 toggle FF in DIL-14 
though, so if you want to replace those a simple 16V8 has more then 
enough resources, but needs an interposer to get the number and 
position of pins correct.  The smallest of the CPLD would replace the 
complete set of four MM5823, but if you insist on using the 5V version 
it's a tiny bit more expensive than four 16V8 (a 3.3V CPLD is cheaper 
than a 5V GAL, though).


Achim.
-- 
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