[sdiy] AN299 and all that !

Jim Patchell patchell at silcom.com
Tue Jun 11 21:27:17 CEST 2002


    Hi Pete...

    As far as the best way to go for expo converters, that is a matter of taste,
somewhat.

    The CA3046 is by far the least expensive chip to make an expo converter out
of.  I have had good results with it.  The MAT04 will give you premium results
at a premium price.  I have used it as well.

    As far as heat vs. tempco resistor?  I prefer neither.

    I am using an electronic scheme at the moment with good results.  The latest
one I did is located on page 10 of this schematic:

http://www.silcom.com/~patchell/seqproj/1001013.pdf

    Don't confuse this with the temp compensation scheme that Paia uses on their
9720 VCO, which also uses an LM13700.  Of course, that is another option (a
circuit diagram can also be located in the National Semiconductor data sheet for
the LM13700).  In my scheme, I use the temperature of the expo pair to adjust
the gain of a simple two quadrant multiplier (made from both halves of an
LM13700).

    -Jim


"Pete G." wrote:

> Hi Guys,
> new subscriber here ! - just re-kindling my interests in building a Modular
> - which began over twenty years ago - but which still haven't come to
> fruition ..!. Maybe this time. Anyone remember a Babani book of sysnthesiser
> projects from about 20 years ago by a certain M.K Berry ? (thats why my
> stuff got shelved !!)
>
> I'm fairly new to the Web DIY synth resources - there does seem to be some
> really excellent material out there, which is great news in a world where
> analogue design is ever more marginalised.
>
> At my last attempt , I knocked up something based on the Nat Semi AN299 VCO
> - had a lot of trouble with the integrator reset circuit ( that 'SCR'-like
> thing). Did anyone ever get that to work reliably ? Got a few ideas of my
> own I'll be trying soon.
>
> Whats best ?  - heated CA3046 / heated MAT04 / LM394 or SSM with Q81 ??
>
> Pete.
>
> _________________________________________________________________
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