[sdiy] Xpander (was: Re: Moog Memorymoog clone almost completed)

[Brian Willoughby]

On Oct 17, 2020, at 11:44 PM, Mattias Rickardsson <mr at analogue.org> wrote:
> Brian Willoughby <brianw at audiobanshee.com> skrev:
>> On Oct 17, 2020, at 11:24 AM, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:
>> > On 16.10.2020, at 23:38, MTG <grant at musictechnologiesgroup.com> wrote:
>> >> What CPU did Oberheim switch to for Xpander? Is that 6809?
>> > 
>> > 2x 6809 (one main, one for the voices) - IIRC.
>> > m.
>> 
>> Yes, and the Matrix-12 has 3x 6809 (one main, one for each of the 6-voice boards)
> 
> What was the typical cost of such a synth CPU in the '80s? Compared to today's 1-2 dollar MCUs they must have been quite an investment.

When the 6502 was designed in 1974-1975, the going rate for a microprocessor and its support chips was around $300 (MSRP $360). A bunch of Motorola designers were unhappy with these high prices, and decided to quit and form their own company, MOS Technology. The chip that they designed was only $25 (target $5). It was also faster. The original 6501 ($20) was pin compatible with the Motorola 6800, but they were legally forced to drop that chip, thus the 6502 ($25) was the one that took off. These were the days of the Intel 8080.

The 6809 is newer, so I don't know how it was priced. It's certainly true that the Z80 was on the inexpensive side. Looks like Motorola dropped the 6800 from $175 to $69, later just $35, and the full set of chips from $300 to $150, thanks to the new competition from MOS Tech. If Motorola could make the 6800 for $35, then I assume the 6809 was comparable.

MOS Technology also went on to design SID around 1981-1982. Bob Yannes didn't work on the 6502, but he did eventually go on to co-found Ensoniq.

The Matrix-12 and Xpander came out in 1983-1984, so I'm guessing not much more than $35 for the 6809.

Note that the $1-$2 MCUs available today are not used everywhere. There are still $10 and even $20 chips in some devices, depending upon the performance needed, and/or the I/O connections (like scanning a velocity keyboard). I doubt that USB can be done for $2. I've noticed that it's quite popular to add a lot of external chips to a simple $1 MCU in order to solve a task, bringing the total cost much higher, and it makes more sense to just pay more for the MCU to get the features needed with fewer external chips.


>> As I noted a while back, there are pins on the main board that could allow four 6-voice boards to be attached, but that feature was never developed. Such a beast would have 5x 6809.
> 
> So, a Matrix-24 then? Wow. :-)
> 
> /mr

Maybe a Matrix-18 would be more practical… (kidding)

Brian