[sdiy] TR-7x7? (was Re: Proms)

[Dan Gendreau]

> > Something I've been wondering about for a while... I *love* the TR-707,
> > but I'm simply not thrilled with the sounds!  I assume these are stored
> > on a ROM somewhere.
>
> They're stored on multiple ROMs, but they could be changed...

> There is a slight internal difference between the 707 and 727 -
> I'd need to
> check the service notes to remember what it is, but it may mean the sounds
> aren't quite interchangeable.
> I've just moved house, so I've not got he workshop set up yet,
> but I've got
> a 727, and I'd quite like to be able to switch it between 727 and 707
> sounds, so I may get round to extracting the ROMs from it sometime. .
> Maybe we could do a swap...
> I've also got an image of the firmware from the 727 (I think it's
> common to
> both) waiting to be disassembled and analysed, but again, no time :-(

I have the service notes here... my copy of the schematics didnt pick up red
very well, and all the tr727 notes on the schematic were in red, so I cant
speak to the differences between 707 and 727. As far as I can tell they are
identical.

The only place I imagine there might be a difference could be in the
envelopes, output levels or panning.

There is a simple R/C analog envelope generator for each drum tone except
for CC/RC. CC/RC are output directly from a 6bit DAC with no envelope, which
explains why the 707 CC/RC sound kinda cheap. All other drum sounds are
multiplexed through an 8bit DAC.

There are 4 32KB Roms, 2 are for most of the drum tones and 1 each is for
the Cymbals.

One thing you should be aware of is that Roland jumbled up the ROM address
pins to improve PCB layout or obfuscate the rom data or both.

The main voice roms are encoded with the following pinout:
IC34(HN61256PC71)
A0-A14=10, 9, 20, 21, 7, 23, 4, 25, 24, 5, 8, 6, 27, 2, 3
D0-D7=11,12,13,15,16,17,18,18
/CS=26, CE=22, Vcc=28, Vss=14

IC35(HN61256PC72)
Same as above, BUT CS=26 (note, CS is active HIGH on this one, not low)

The Cymbal roms are encoded as follows:
CC=IC19(HN61256PC73)
A0-A14=9,10,8,7,20,21,6,4,5,3,2,27,25,24,23
D2-D7=13,15,16,17,18,19
/CS=26, CE=22, Vdd=28, Vss=14

RC=IC22(HN61256PC74)
Same as CC, but:
A0-14=20,21,23,24,3,27,25,9,10,8,4,2,7,6,5

I have both the 707 and 727, and I must agree with Drew... I love the
TR707/727 user interface, much more than the 909, but I hate the sounds. If
I had the time to break out the individual drum triggers, it would make a
fantastic front end to any analog drum tone project.

I do not have an EPROM programmer, but if you can rip these ROMs and send
the data to me for testing, I can write you all a windows app to decode and
encode them from WAV files. I also have a couple of BOSS DRPads that work on
the same Counter/ROM/DAC principle, so this could turn into an interesting
little application. It could be configured for almost any ROM based drum
machine.

Ideally, It would be cool to substitute in a larger rom with many banks to
chose from. Better yet, use a uC to download sounds to SRAMs via Sysex! But
alas, I havent had the free time to tackle any of that yet. :)

-Dan Gendreau