[sdiy] Expo in one chip?

[Jacob Watters]

Ok. Thanks for the help. I haven't experimented with the 2164 yet. I will
have to get some to test out.

On Dec 26, 2017 6:29 PM, "David G Dixon" <dixon at mail.ubc.ca> wrote:

> That's an old version.  I've replaced the two transistors with another
> 2164 VCA, and you don't see the actual expo converting 2164 in that
> schematic, but it takes the Expo VC output of the opamp and directly
> processes the VCO core current.
>
> The parts count really isn't that high.  Almost all of the parts on this
> schematic are input resistors and pots for controlling the pitch, and these
> are all going to be required no matter what.  The HFC circuit requires two
> trimmers because my scheme adjusts both the slope and the intercept of the
> correcting current, unlike most schemes which only control the slope.  This
> is the key to the Dixie's (and Rubicon's and Atlantis's) excellent
> tracking.  Again, even an all-in-one expo converter chip would require
> external correction trimmers, because every VCO core has tracking error.
>
> I don't mean to presume anything about your design skills or level of
> experience, but I think that if you really went carefully through a VCO
> design, then you would realize that what you are asking for really wouldn't
> save very much in terms of parts or labor, both in building and in
> calibrating.
>
> ------------------------------
> *From:* Jacob Watters [mailto:jacobwatters at gmail.com]
> *Sent:* Tuesday, December 26, 2017 1:58 PM
> *To:* David G Dixon
> *Cc:* SDIY
> *Subject:* RE: [sdiy] Expo in one chip?
>
> Thanks David. Like this example posted on muffwiggler?
>
> https://www.muffwiggler.com/forum/userpix/2077_dixie_cv_network_2.png
>
> That sovles the resistor contact issue, but it still has a high part
> count. Is there no such thing as a chip with linear in on one pin and expo
> out on another?
>
> On Dec 26, 2017 4:07 PM, "David G Dixon" <dixon at mail.ubc.ca> wrote:
>
>> Yes, it's called the V2164, and it is available from Coolaudio in bulk,
>> or from many retailers (Small Bear, Mammoth, etc).  It is a quad
>> exponential VCA chip.  One VCA is used to temperature compensate the expo,
>> and another is used as the actual exponential converter.  It requires an
>> external summing opamp.  A third VCA can be used as a precision
>> high-frequency compensation current source, leaving the fourth VCA for
>> another use.  This is how all Intellijel VCOs (which I designed) are
>> controlled, and they have a reputation in euro-land for very decent
>> tracking and stability.
>>
>> ------------------------------
>> *From:* Synth-diy [mailto:synth-diy-bounces at synth-diy.org] *On Behalf Of
>> *Jacob Watters
>> *Sent:* Tuesday, December 26, 2017 12:49 PM
>> *To:* SDIY
>> *Subject:* [sdiy] Expo in one chip?
>>
>> Expo conversion is require in almost all VCO, VCF and VCA circuits.
>> Matching transistors and getting the right tempco resistor to be touching
>> them so they are the same temp is a pain.
>>
>> Has anyone ever made an expo conversion chip that had everything required
>> in one package? Is it still available?
>>
>>
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