[sdiy] Cheetah MS800 replacing NiCd Varta Mempac

Steve Lenham steve at bendentech.co.uk
Sat Jun 5 12:03:10 CEST 2021


Any chance that you could post some decent pics of the MS800 circuitry?

The MS800 is one of those units that has become mythical mainly because 
there is hardly any solid information about it in free circulation, so 
it can be whatever anyone wants it to be. I'm curious as to what the 
fundamental sound generation circuitry is based around.

Now, I was about to post the following:

"No offence to Cheetah, but they were not the sort of firm that I would 
expect to have developed some unique circuitry. Much more likely that it 
is a clever (or not!) implementation of something off-the-shelf.

I'm guessing either:

1. One of the early Dream Synthesis digital synth ICs (like in the 
Evolution EVS-1).
2. One of the SGS(ST) ROM playback chipsets designed for organs (Mxxx 
series).
3. Perhaps something by TI Italy (TMS3xxx series)."

...when I thought that perhaps I should do quick Google to see whether 
anything new had been discovered recently. And there was a little.

According to Vintagesynth, the MS800 was designed for Cheetah by an 
external consultant, Mike Lynch of Lynett Systems. And the consistently 
reliable polynomial.com reveals that it does indeed use an SGS chip 
reading waveform data from a 27256 EPROM, with a 6502 CPU managing the 
system.

They can't read what the IC is since it is covered with goo, but I would 
put money on it being the M114. Polyphonic? Tick. Multitimbral? Tick. 
Reads waveform data from EPROM? Tick. Can you confirm, Richie?

For those tempted to have a tinker, the M114 was definitely used in '80s 
digital organs. It would be good to identify which ones. I picked up a 
set of four PCBs from an unknown organ on eBay for peanuts - each 
contains two M114s reading data from EPROMs labelled "Celeste", 
"Diapason" etc.

There seem to be at least two versions - my boards use the M114S, which 
has 40 pins, while the datasheet I have is for the M114A which has 48 
pins. Polynomial's photo of the MS800 shows 40 pins.

So anyway, all we need is for Richie to trace out the circuitry of his 
MS800! We can then make MS800 clones using cheap organ parts and get 
rich selling them to Aphex Twin fans :-)

I love me a bit of nerd archaeology :-)

Cheers,

Steve L.
Benden Sound Technology

P.S. Re the battery, just fit the NiMH replacement and check it every 
ten years for signs of leakage starting - or more regularly if you allow 
it to sit completely flat. Although one should always do due diligence, 
at that level of charging current (1.4mA!) there really won't be any 
NiCd/NiMH compatibility issues. Extending it off-board is also a good 
insurance policy, if you are willing to put in a bit more effort.


On 04/06/2021 19:34, Richie Burnett wrote:
> Lol. Richard D James has got a lot to answer for! It's a totally bonkers synth, with a very gritty sound.
> 
> -Richie,
> 
> ---- Gordonjcp wrote ----
> 
>> On Thu, Jun 03, 2021 at 03:29:59PM +0100, Richie Burnett wrote:
>>>
>>> I would be interested to hear your thoughts!
>>
>> The overriding one I have is "I wish I hadn't passed up that MS800 that was in Vic Morris for 50 quid about 15 years ago..."
>>
>> -- 
>> Gordonjcp
>>




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