[sdiy] Understanding 80s Synth Architectures

[Nathan Trites]

Focusing on polysynth/polyphonic sampler architecture was how I spent my
winter so far. To echo previous recommendations: Musical Applications of
Microprocessors is excellent, as well as the SCI Prophet 5 service manual,
Rhodes Chroma site and service manuals.Other SCI service manuals are good
too.

For the computer side, I don't have many specific recommendations beyond
those, but various intro to Z80 and 86k processor sites and courses
<https://www.cs.mcgill.ca/~cs573/fall2002/notes/lec273/lecture8/>I've
stumbled on through searching have been helpful to get a better
understanding of memory mapped computers in general. There is also a huge
retro computer scene now, and some Youtube channels like Adrians Digital
Basement, Noel's Retro Lab and similar have in-depth videos on debugging
computer problems that can help fill in the gaps missing from synth repair
info online. I struggled to find good resources specifically for fixing
embedded computers from the 70s/80s that would have been targeted towards
service techs but would love something like that.

Nathan

On Fri, Feb 4, 2022 at 5:22 AM ackolonges fds via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Hi Everyone,
>
> As the local SDIYer I sometimes get asked to try and fix synths from the
> 80s like various Rolands, Korgs, Oberheims etc. and I generally just try to
> pinpoint the rough area of the issue and replace logic chips until the
> issue is resolved...
>
> Most of these synths have a CPU connected to everything via a parallel
> address bus and a parallel data bus, with all sorts of glue logic chips
> doing various things. They also usually just have 1 DAC, time-domain
> multiplexed to all of the different parameters via more logic chips.
>
> Obviously this is very different to the modern ways that microcontrollers
> and DACs are used in synths, and since I wasn't around in the 80s, these
> older architectures are very foreign to me. To aid in my troubleshooting
> efforts, I would love to better understand the details of how these
> architectures work, so I was wondering if anyone on here would be able to
> point me to any resources that could explain these types of systems to me,
> be they websites, articles, or books?
>
> Thanks a lot for any advice you might have.
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