[sdiy] 10 octave VCO circuit from EDN June 4 2025

[Oren Leavitt]

Nice design!

I think this can be easily adapted, with level shifting maybe, to work 
with our familiar synth expo converters.

1N457 was a go-to for low reverse leakage diode back in the day. It 
seems to me nowadays most modern-process vanilla 1N4148 diodes have low 
enough reverse leakage to get you down into the nanoAmps range comfortably.

Gonna have to knock something together and play with it.

- Oren

On 6/7/25 12:37 PM, Roman via Synth-diy wrote:
> I think it will be good enough with plain BC857BS but the key here is 
> low leakage diode that flips the mirror to expand usable tuning range at 
> low end.
> 
> Maybe it's better to replace it with transistor.
> 
> Anyway IMHO the expo converter will spoil the tuning response more than 
> any mismatches in this innovative VCO core.
> 
> 
> Roman
> 
> 
> Roman
> 
> 
> ---- Użytkownik René Schmitz napisał ----
> 
> 
>  > On 07.06.2025 08:26, Paul Perry via Synth-diy wrote:
> 
>  > > https://tinyurl.com/57fd674d <https://tinyurl.com/57fd674d>
> 
>  > >
> 
>  > Hmm, interesting to see NTC for temperature compensation, and (buffered)
> 
>  > ARP style exponentiatior . Looks somewhat similar to my VCO4069.
> 
>  >
> 
>  > That bidirectional current mirror is quite intriguing. I wonder how good
> 
>  > the symmetry it is, and how well the transistors have to be matched.
> 
>  >
> 
>  > Cheers,
> 
>  >
> 
>  > René
> 
>  >
> 
>  > --
> 
>  >
> 
>  > --
> 
>  > synth at schmitzbits.de <mailto:synth at schmitzbits.de>
> 
>  > http://schmitzbits.de <http://schmitzbits.de>
> 
>  >
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