[sdiy] MS-20 Filter Clone Queries

[Kyle Stephens]

Well, it's just that this expo converter, using a pair of NPNs...:

http://www.uni-bonn.de/~uzs159/expo_tutorial/fig3.png

(as seen here: http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html) 

...looks like the expo converter in the MS-20 schematic, using PNPs, turned about some.

Bearing that in mind, and using my extensive graphics skills, let me ask if this would work:

http://i10.photobucket.com/albums/a102/erschlagener/expo.jpg
(R5 that I labeled tempco would be glued to the LM394 pair)

I know how haphazard a solution this sounds like ("this kinda looks like that 'graphical interpolation'"), which is why I'm asking if it's correct in any event - if it's right, I can figure out things backwards and get the theory down once I know what will function (and in the future, figure things more methodically). Otherwise I'm certainly open to more involved or alternate solutions if mine's garbage.


_Kyle


--- On Tue, 12/2/08, Ian Fritz <ijfritz at comcast.net> wrote:

> From: Ian Fritz <ijfritz at comcast.net>
> Subject: Re: [sdiy] MS-20 Filter Clone Queries
> To: lightburnx at yahoo.com
> Date: Tuesday, December 2, 2008, 4:42 PM
> At 03:09 PM 12/2/2008, you wrote:
> > I'm building an MS-20 filter clone, as seen here:
> > 
> >
> http://electro-music.com/forum/phpbb-files/ms20_13700version_142.gif
> > 
> > In regards to the cuttoff CV expo converter, I
> haven't any matched PNPs lying around but I do have a
> few LM394s (matched NPNs) I got cheap from Futurelec.
> There's some simple rearranging I can do to make the
> NPNs work, right?
> 
> 
> No.