[sdiy] 2164 Expo VCO tracking

[karl dalen]

>  5V: 13755    (14080 
>    -2.31%)
> 
> Note that the VCO was set to oscillate at 440.0Hz at a CV
> of 0V by adjusting
> the panel pots, the CV summing amp feedback trimmer was
> adjusted to optimize
> LF tracking, and then the HF trimpot was adjusted to
> eliminate error at
> 3520Hz.  The octave voltages were generated by the
> six-octave selector
> switch on my custom scanning keyboard, which selects from a
> ladder of
> hand-matched 100k 1% resistors.  I went from the
> lowest A to the highest A
> on my keyboard above 880Hz and readjusted the 440.0Hz point
> to read the
> values above 440Hz.
> 
> Obviously, the tracking falls apart much above 7kHz, but
> you can't really > discern pitches above that.  The tracking is more or
> less perfect within the  musically useful range, except for the octave >around 1V,  which is always a  bit sharp (I don't know why).

I wonder if the last Ota are driven into gain mode and that causes 
internal heating and/or creates current offsets thats large enough to
cause more current into core then needed? But yet your breadboard
figures seams OK....

How did you come to the 500k on the AB mode pin? By calculating internal 
beta of the core? What if this are set wrong and causes a shift at a certain point?

One thing i have seen are if a 2164 ota are used in a triangle core loop
a increase in gain of wave occur just before 0V CV.I figure the core enter active/bost mode which should be avoided when used for osc applications. But i might be wrong in my assumptions.But it did go very unlinear.

Have you tried to simply shift the operating frequency of the core by swap
the charge cap up or down, lets say from 1n to 470p.

KD

 

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