[sdiy] Patchell's Boggling 13700 Expo Converter Thing???

[Scott Bernardi]

It's not just a simple V to I conversion. You have to do a multiplication of
Vin times a PTAT term. An OTA is one of the simpler multipliers.
I believe the CEM3340 uses a similar scheme for temperature compensation.

Jay Schwichtenberg wrote:

> I've wondered about the S/N of the circuit with 2 realitively noisy OTAs
> (compared to a good or high end op-amp) in the audio path. To me it seemed
> like the issue of the advantages and why of the circuit have been skipped.
> Could just an op-amp V to I converter accomplish the same thing?
>
> Jay
>
> > -----Original Message-----
> > From: owner-synth-diy at dropmix.xs4all.nl
> > [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Oakley Sound
> > Sent: Monday, June 23, 2003 1:39 AM
> > To: synth-diy
> > Subject: Re: [sdiy] Patchell's Boggling 13700 Expo Converter Thing???
> >
> >
> > > I found another reference...It looks like Tony has been using the
> > > circuit as well...
> > > http://www.oakleysound.co.uk/vca-doc.pdf
> >
> > Yes, I took my idea from the EDN circuit. I changed it a little bit, but
> > its more or less the same. I don't think its quite as good as Mike Sim's
> > suggests in the article, but I can't measure THD/noise that accurately
> > in my little workshop. So it may well be. Simple tests make it a
> > maginally better circuit than either CA3280 or BA6110 operated singly.
> > [better S/N, better CV rejection]
> >
> > Regards,
> >
> > Tony Allgood                       Penrith, Cumbria, England
> >
> > Oakley Sound Systems                   www.oakleysound.co.uk
> >
> >

--
Scott Bernardi
sbernardi at attbi.com