[sdiy] VCO that goes SHARP in highest octaves??

[Michael E Caloroso]

Wow glad that witch hunt was solved.

MC

On Thu, Jul 14, 2022 at 7:13 AM Ian Fritz via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Ah, glad that got it!  I agree with Phil on including the series Iabc
> resistor.  It can also ensure that the max current won’t be exceded, and
> someone once suggested it could help with inaccuracies caused by the Early
> effect.
>
> Ian
>
> > On Jul 13, 2022, at 11:06 PM, Neil Harper <metadata at gmx.com> wrote:
> >
> > On 6/17/22 14:04, Ian Fritz wrote:
> >> Something else you might try: reduce the values of the integrating cap
> and the reference current by a factor of two or so. This could possibly
> reveal any self-heating in the expo transistors.
> >>
> >> Ian
> >
> > We have a winner!
> >
> > Reducing the integrator cap and reference voltage by a factor of 2 as
> > Ian suggested now has the VCO working as expected.
> >
> > (cents)    C4    C5    C6    C7    C8
> > BEFORE    0    0    0    +5    +13
> > AFTER    0    0    -1    -2    -4
> >
> >
> > The flat higher octaves were easily trimmed out with a very small amount
> > of added HF-Trim exactly as expected.
> >
> >
> > I haven't tried Phil Macphail's suggestion yet though of adding a
> > resistor between the expo pair and the 13700's Iabc pin. Is there an
> > advantage to either solution?
> >
> >
> > --
> > /// Neil Harper
> > /// Every Wave is New Until it Breaks
>
>
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