Eric Schlaepfer's "Goodgreat DS3" Clones the Classic Greengate DS3 Apple II Sampler — From Album Art

The cover art of a 1984 12" album brings a piece of wavetable synthesis history back from the dead.

Gareth Halfacree
1 month agoRetro Tech / Music / HW101

Eric "Tube Time" Schlaepfer has built a clone of the Greengate DS3 Apple II sampler card, reverse-engineering the original from an unusual starting point: an album's cover art.

"I've reverse engineered a printed circuit board using ARTWORK FROM AN ALBUM COVER," Schlaepfer writes of the project, referring to the 1984 album Into Trouble With The Noise of Art by Mainframe — who worked with Greengate on the board's development. The cover of said album was an illustration of the top layer of the PCB for Greegate's DS:3 sampling card — showing exactly what connects to where.

"[The DS3] is an obscure wavetable synthesis card for the Apple II from 1983," Schlaepfer explains. "Naturally, I don't have a physical board, but I have a blurry photo of the back. And, of course, the artwork for the top layer. which is great, since I can see traces that would normally be obscured by chips and other parts."

Using these, Schlaepfer was able to begin a KiCad 7 project — importing the images and using them to guide the layout of footprints and traces. "I just add a wire at a time to the schematic, propagate it to the layout, and make sure that it matches the existing traces," he writes. "If there is any ambiguity, I just move on to the next trace. Eventually I use a process of logical deduction to resolve that."

That resulted in board that matched the original, with one slight problem: although high-resolution imagery of the board's front was readily available, one of its chips had been relabeled by someone at Greengate — and when an owner of an original board pulled the chip, its underside had been erased and the message "YOU NOSEY S.O.B." scratched in its place.

"This chip seems to take over the Apple II's address lines and it copies sound samples over to the four DACs [Digital to Analog Converters] on the card. Almost like a DMA [Direct Memory Access] controller. It perfectly matches the pinout of the [Motorola] MC6844 DMA controller! Mystery solved."

With the last chip identified, the replica board — dubbed the Goodgreat DS3 — was complete. "Not all the components are readily available," Schlaepfer admits. "In particular, the ZN428E DACs, ZN448BE ADC [Analog to Digital Converter], AM9513 timer, and MC6844 DMA controller are no longer made and will need to be purchased from a surplus electronics store or online auction site."

The KiCad project files for the board are available on GitHub, under the Creative Commons Attribution-ShareAlike 4.0 International license; a write-up on the reverse engineering process has been published to Mastodon.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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