[sdiy] Jim Williams Oscillators

[cheater cheater]

On Fri, Feb 22, 2013 at 12:57 AM, Neil Johnson
<neil.johnson97 at ntlworld.com> wrote:
> cheater cheater wrote:
>> Many synths have diode clippers in the feedback path in order to
>> change the loudness of the resonance vs the rest of the response, for
>> one thing. It's very practical.
>
>
> No, it's a cheap brute-force way of controlling the "oscillator"
> amplitude.  It results in significant distortion, which probably
> accounts for the characteristics that some people like in certain filters.
>
> A good sinewave oscillator (e.g., a filter with resonance turned up to
> cause self-oscillation) needs just the right amount of feedback - the
> lamp in Wien bridge circuits being a classic example.  Too little and the
> oscillations will decay; too much and the oscillator will happily distort
> into its rails.
>
> The late Jim Williams put considerable effort into amplitude control in
> his low-distortion sinewave oscillators, compared to the relative
> simplicity of the oscillator core itself.  Some oscillators have
> multiple amplitude control loops to achieve the required performance
> characteristics (distortion, step response, etc).

Hi Neil,
would you happen to know some designs of such sinewave osc's that are
not too difficult to build? It would be cool to have something good
for measurement. I'm thinking of constant-frequency but also of ones
that can be sweeped (I bet there's a difference)

Cheers,
D.

> Cheers,
> Neil
> --
> Modules and more :: www.cesyg.com
> Homepage :: www.njohnson.co.uk ::
>
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