[sdiy] Jim Williams Oscillators
cheater00 at gmail.com
Fri Feb 22 12:23:29 CET 2013
Thanks, Phil! That should have me reading for some time.
On Fri, Feb 22, 2013 at 12:02 PM, Phil Macphail
<phil.macphail at liivatera.com> wrote:
> 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)
>>> Modules and more :: www.cesyg.com
>>> Homepage :: www.njohnson.co.uk ::
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