dr 550 practical mods?

[lazydog]

1st question: is there a way to add a 3v memory backup battery to dr550?
could be a simple thing..seems it relies on having 6xAAs in there, or the
memories wipe when you power off. pretty weird.

2nd: do you have any recollection of useful pinouts from chips? (share?)
(would like to see if sample tuning/independent outs/etc is possible)

3rd: (less crucial now, as have come to terms with lack of:) midi out? possible?

i still love it though. 

[Circuitbenders]

I've done one http://www.circuitbenders.co.uk/newsarchive/DR550.html although in hindsight i probably wouldn't use a patchbay if i did another one. Most of the effects seem to tail off and fade away after a quick connection, so they are probably more suited to switches or even pushbuttons.

You'd probably need some schematics to figure out if a lithium battery backup was possible. Theres definately some discussion of how to do this to do with another drum machine somewhere else on this forum, so that might be a starting point. The main issue would be to stop the DR550 trying to run from the backup battery and eating it in a few hours.

Independant outs, tuning and midi outs won't be possible unless you fancy rewriting the firmware, which you really don't 

My notes show a diagram of a chip labelled Roland, and say i used pins 2, 3, 5, 7, 8, 9, 10, 11, 12, 14, 15, 17, 18, 19, 20, 22, 23, 25, 26, 28, 29 and 31 on that chip. Hopefully thats with the standard pin numbering.

[lazydog]

a-haa: have found the service manual on that czech (?) site.
here is: http://www.box.net/shared/xhabjdvpo5s5burh9f6e

(hope i posted the right link!) it shows block diags etc. inc'
power+backup section. you might be able to make sense of
that for a neat fix.

any chance you could up those notes on the pinouts you id'd?
(just out of interest: anything complicated is ruled out, but you
never know, if something sensible is accessible...)
in fact, i really like this machine: managed to suss it out quite
quickly(with manual) -lol, that's something pretty terrible you
inflicted on it! haha. i was thinking of something a bit more
sympathetic shame i haven't got the mkII version with more
sounds, but these are ok, i just don't want to have to keep
resetting all the pad assignments due to power drop.

[Circuitbenders]

'Pretty terrible' is about all the DR550 does in circuitbending terms. It doesn't even have a passing acquaintance with subtlety.

On page 7 of the service manual theres a schematic. From the look of it the chip i'm talking about would be IC3 - ROM, just to the right of that massive chip in the middle labelled IC2. According to my notes it says Roland printed on it. Its pretty easy to find it on the upper right of the main board diagram on the previous page

[lazydog]

so those would give me outputs/inputs of various functions?
tbh, not too keen to muck this fella up. but woul dbe useful
to have an idea of what kind of things i'd find on those pins


can you see anything suggesting it might be feasible to put
in a 3v backup cell? i'm ok now with the idea of keeping 6(!)
LR6 AAs in there to retain memory; i got the psu with it, so...

so far, it's a good beat toy. i suppose if i wished for anything,
it might be pitching of drums? or adjustment of indiv volume.
or a split out for something...i can see midi out is out of the
question

[Circuitbenders]

I'm not sure what you mean by 'outputs/inputs of various functions'. Just try shorting together the pins of that chip and see what happens. Most of them will distort the sounds but theres some other interesting stuff on there. I think you might have overestimated just what can be done with a unit like this in terms of circuitbending.

You could probably replace the crystal or ceramic resonator at X1 with a LTC1799 module to control the pitch but it'd probably control the speed of the operating system at the same time.

You could try and find the datasheet for the RAM chip and see how much voltage it needs for data retention.You might as well just leave some batteries in there though.  Isn't there already a battery on the board?

[lazydog]

ok, so i'll forget about mashing up the sounds etc.

apparently no internal battery...you retain memory by leaving AAs in there,
and have around 60secs to replace them when you remove them, according
to what i've read. it kept dumping memory before i put them in, so i did
figure dead internal, but before desoldering the shield board i found it doesn't
have one (does it?!! well i think not)

of course i left it switched on last night..(.but batteries not killed yet).

[gmeredith]

In essence,  you would provide a 3V DC supply from a lithium battery to the Vdd (+5V) power pin of the SRAM chips, with a reverse flow diode attached to the + terminal of the lithium battery to protect it against charging when the power is on. This is on page 7 of the service manual - pin no. 28 on a chip marked IC5 "SAM2064M-15". You can see already that the chip pin 28 connects to an arrow labelled "Bu", meaning "Battery unit" - the chip gets its backup voltage when powered down from the batteries in the Dr550.

The neg. terminal of the lithium battery would connect to the Vss pin no. 14 of the chip (0V, gnd).

Cheers, Graham

[lazydog]

thanks for the info. was hoping for something like that. could be
viable if enough space inside; meanwhile i'm living quite happily
with it   i believe i can record the tape storage out into a PC
if i get the level...

[lazydog]

another t'ing... MIDI out...is that just a fantasy, with this? just asking...
really pretty odd they didn't put it in.

and the last t'ing: is there any possibility at all of tapping a separate audio
out for any of the individual sounds? already pretty certain that is a no,
since the audio mix probably occurs within the sound generation chip.

[Circuitbenders]

i refer you back to my first reply up there. 

Independant outs, tuning and midi outs won't be possible unless you fancy rewriting the firmware, which you really don't 

[lazydog]

erm yeah, so you did...fair enough