[sdiy] TR909 clone PCB pictures

[Trevor Page]

> Change 1 bit in the EEPROMS, or implement it differently, or use one BIG
rom
> and put all the sounds on the same rom and let a micro play it from memory
> addresses ...

> ...(which I am actually surprised this wasn't done)

For a number of reasons, the main one being that a relatively fast processor
would have been required in order to retrieve and play back the sampled
sounds simultaneously, and with each being tunable. Okay yes, that's a
relatively easy thing to do with your average PIC / AVR, and at one stage I
had actually opted to implement it this way - but I realised that all this
would have been a bit of an overkill for a circuit which works just as well
as it does, and I wasn't really aiming to enhance it. I wouldn't bother
going into the trouble unless I was wanting to build a full-blown ROMpler,
which was way out of scope of my original specs: i.e. a 909 'copy'.

> Better yet, change it to static ram and let the user change the sounds at
> will, to anything they like! ;)

Yep, that's a good idea. But that really does considerably change the whole
thing. Again, it's meant to be a clone of the classic drum machine, and
little else. Your suggestion is a great project in itself (IIRC, Paul Maddox
is doing a drum module that way), but I don't think it would be necessary in
what's meant to be a 909 clone.

I had many suggestions, such as improving the EPROM circuits so that extra
sounds could be stored, voltage/MIDI control capability of all parameters,
hardware / software LFOs, the list goes on :) but with barely enough time to
complete the project as it is (I've been at this for at least a couple of
years) I had to freeze it somewhere.

Heh, heh... I feel I may be opening a good few cans of worms there :o)

Cheers,

Trev

> Rob