MS20 ESP Simulation (WOW)

[Harry Bissell]

I've simulated part of the MS-20 ESP (TomG / Korg) and got a big surprise.
I'm only looking at the part I didn't understand (re: the converter). The
first two comparators form a zero crossing detector which fires a positive
pulse to the converter.

At low frequencies (below about 1.5-2K) the converter froms a one shot
multivibrator which gives a pulse every input cycle (as I expected...)

Above that, a strange (and wonderful) thing happens. The pulses begin to
overlap, and the off time (zero) becomes fixed. So you get one, two, three,
four cycles of positive level and then a fixed zero...

Not at all what I expected to see. I don't understand yet how it is
happening... but it seems to work. This extends the range of the scheme
above where the "tachometer" circuit should fail.

Above 5K the pulses go to a permanent "high" level and the output voltage
can't rise any further... But that should have happened two octaves ago...

I don't know why the output filter is linked to the "low cut" input filter.
Somebody help me out ???

BTW if you got your ears on, JH.... isn't Korg engineering wonderful...
I wish they hurry up and put the "Empire" out of business !!!

:^) Harry

tomg wrote:

> From: "tomg" <efm3 at mediaone.net>
>
> Maybe I should just email this direct to D******* (sp?). I thought it
> over really well before posting it. I have worked on this off and
> on for over a year and would like to share it with the people who
> made it possible. Paul,  if you want to build something for the
> axe-slingers down where you are you have a right to, it was at
> your urging I started this in the first place and to the people who
> sent me info on the ESP thank you too, you know who you are.
>
> http://www.geocities.com/efm_gc/cbook/pics/esp-sd.gif
>
> There are no intentional errors. I mixed up the output labels but
> as far as I know if built as shown it works. How well it works is
> another question all together...I don't really know. I don't have
> access to a ms20 to compare them.  It's not designed to drive
> a V/Oct VCO and that's all I have now that the FatMans gone...
> So....??.......I can get it to track the output of a synth to a VCO
> pretty well as long as I'm not expecting miracles. It's a lot better
> than I expected. I don't know about plugging a guitar into it yet
> because I put it away to do the CAM stuff. I have not gone
> back to it yet and don't expect to for a while. Maybe one of the
> guys who really wanted this will build one and tell us about it.
> WARNING don't expect miracles but it's fun.....;-)
>
> -tg
>
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