[sdiy] Jim Williams Oscillators

Phil Macphail phil.macphail at liivatera.com
Fri Feb 22 12:02:59 CET 2013

For Jim Williams designs, this app note is a decent start -

The same concepts return in some of his later notes on sine oscillators, but this is where it starts,


On 22 Feb 2013, at 11:08, cheater cheater <cheater00 at gmail.com> wrote:

> 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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