Good designs of Expo Converters? Was: [sdiy] Multiplexed Expo Converter?

[Aaron Lanterman]

On Aug 1, 2009, at 12:38 PM, cheater cheater wrote:

> Scott,
> thanks for your answer. I didn't know expo FM was inharmonic, I'll
> need to check that stuff out, it sounds really neat actually -
> inharmonicity is one thing you can use to make sounds much more
> interesting.

I've seen a detailed analysis of exponential FM somewhere, but I can't  
remember now - maybe electronotes? Wait - I think I might have seen it  
in a book Dan Snazelle showed me over coffee. Maybe it's in  
electronotes too. Or neither. Brain fuzzy.

Dan, what was that book you showed me?

> On another note, PM is sort of like FM but not - it's
> very fun - check it out if you ever get a chance. Patch something
> across an accumulator cap or something (it would be more involved than
> that to get real Phase Modulation but might give you some form of
> foretaste)

If you're modulating a sinusoid with a sinusoid, PM and FM are sort of  
equivalent, since the integrals and differentials of sinusoids are  
also sinusoids:

http://www.clavia.se/nordmodular/modularzone/FMsynthesis.html

> Guys, what are some good designs of Expo Converters?


The classic is the Electronotes/ASM-1 type; it's what I teach in my  
"Electronics for Music Synthesis" class. My lecture notes are based  
off of the description of operation on Rene Schmitz's page: http://www.uni-bonn.de/~uzs159 
. I can't recall for sure now, but I think I refer the students to Ian  
Fritz's pages if they're interested in deeper analysis.

See Session 8: http://users.ece.gatech.edu/~lanterma/ems (and see  
session 7 for a discussion of the sawtooth core, based on the  
discussion in "Musical Applications of Microprocessors."

I also talk about it in my earlier version of the course, http://users.ece.gatech.edu/~lanterma/ems 
, but I'm not sure where the expo discussion is (probably in the  
Sawtooth Core or Triangle Core lecture but I don't remember which).

- Aaron