[sdiy] Expo converters ( uh-oh, I started reading EN... )

[Tom Arnold]

A couple quick questions for y'all both pertaining to expo converters in
Electronotes.

First question pertains to the VCO described in ENS76 option 1A, also EN37
page 4 Fig F.  For those without EN handy this is your run of the mill two
NPN's from a CA3046 expo with a third transistor from the 3046 acting as
active compensation for bulk resistence.  Concerning that 3rd transistor,
does it have to be matched to the pair in the expo itself?  What I have in
mind for playing with is to use an Option 1 VCO which is based around the LM394
and add the compensation circuit.  I figured I'd at least thermally couple
the compensation transistor, but matching wasnt planned.

My second question is about another Expo is in the same EN.  This ( EN37 page 3
Fig E ) is the good'ol Arp pnp/npn pair but with a pnp/npn pair
compensation circuit.   I havent seen this used much besides, well, Arp and
never with the compensation.  I was thinking of trying a THAT340 since it
seems to fit the bill and is pretty darn affordable.  Besides the fun of
playing with it I'm worried that it just doesnt work well enough to persue,
mostly based on not seeing anyone else using this particular circuit.  Is
that fear proven, or is this just not a circuit people have played with
much?

Can you tell my fixation is on VCOs right now?

Thanks!

-- 
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 - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
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