INSIDE A ROLAND - D550

[Artesia]

Heres an interesting bit of synth history, the roland d-550 - their first digital synth i believe; which was built on the principal of digital emulation of analog synthesis oscillators + filters & envelopes ..with the addition of a wave engine which played rom stored short snippets of sampled audio to give an initial realistic attack portion (or crude audio loop) over layered ontop of a more conventional virtual 'analog' patch.

also this synth features eq, chorus & reverb (and others i may forget) ..everything done in the digital domain to make it at all affordable for the era :)

its far from perfect, which is what makes it particularly interesting, full of noise, aliasing artifacts and its very rough round the edges.

it maybe possible to tune out some of the less desirable artifacts if one cared to do so; by piggybacking on a more refined DAC section (anyone up for making a parallel to serial converter with afew stock logic ic's ? ;) ); and the existing one could be improved a little if you really wanted to start messing with its original design.

the DAC section consists of a mono 16 bit DAC (pcm54hp), which works on a parallel interface ! ..and stereo output is achieved through toggling the output between left and right channel with a 4066 silicon switch. this switching mechanism in particular i feel could be improved & maybe the most significant acheleies heel in introducing the least desirable of the artifacts present :)

TOP RIGHT:

32.768 XTAL

ROLAND (CUSTOM) - R15229851 / MB87136A / 8735 E83

ROLAND (CUSTOM) - 532000P-7474

ROLAND (CUSTOM) - 532000P-7473

RIGHT-LOWER:

12MHZ XTAL

ROLAND (CUSTOM) - R15229849 / HG61H25B18F / 7K2

HITACHI - HM6264ASP-15

HITACHI - HM62256LP-10

ROLAND (CUSTOM) - R15229848 / D65005G062

NEC - D78312G 022 / 8739PX700

TOP-LEFT:

ROLAND (CUSTOM) - R15229842 / MB87137 / 001 / 8743 E47

ROLAND (CUSTOM) - R15229866 / MB87126A / 006 / 8743 Z81

HITACHI - HM6264ASP-15

? - MB81416-10

OUTPUT:

C4570HA

M5216L

LEFT-LOWER:

BURR BROWN - PCM54HP

? - D4066 (4066 ANALOG SWITCH)

OPAMPS - 5238 ? & 4570

DAC section.

[stryd_one]

I think the ROMs (532000) are standard rather than roland custom.... Is it just me, or does the silkscreen imply the possibility of adding more?

[Ashiman]

there supposed to be analog filters that arent anti aliasing righT?

[Artesia]

the silk screen is the underside of the soldered on rom board :)

chips present.

no idea about the 535's being a generic rom chip; never seen them in my life in this format outside of roland rom cards ..tho maybe the local coin op specialist knows of them from elsewhere too ;) :)

of note tho, when certain rom banks where required in large numbers, some company's actually had the chip fabbed with the data already on the die as part off the silicon manufacturing process itself ..somehow, that turned out cheaper than flashing generic chips for some company's. apparently apple did this back in the day with certain chips.