Re: gEDA-user: challenge board ALMOST works

[Dan McMahill <dan@xxxxxxxxxxxx>]

John Luciani wrote:

> > Here we go...  Do you have the manual for the etherwave?  Last paragraph
> > of the left column of page 6.  Basically the 2 caps which combine the
> > fixed frequency oscillator and the variable frequency oscillator for the
> > pitch circuit not only combine the signals into the mixer, they also
> > couple the oscillators so that they will injection lock to get a stable
> > "zero beat" when you step away from the theremin.
>
>
> You are right. I do not have the Etherwave manual but the Bob Moog
> article (Electronic Musician Feb96) states that the oscillators should
> be separate so that they won't couple but that the capacitiors will
> lightly couple them so that they synchronize at low beat frequencies.
>
> Thanks.
>
> Is this injection lock primarily used to prevent a small amount of
> oscillator drift from producing an audible tone at the low end or is
> it just to increase the change in capacitance
> required to get an audible tone? The pitch oscillator is tuned to apx. 
> 200KHz so
> a 0.01% drift (20Hz) would produce an audible tone.

I think that avoiding audible tones is exactly what this is for.  You do 
have to be careful because the larger the coupling, the wider the 
injection locking range (in freq.) is.  So you want enough to avoid 
audible tones when you step away from the theremin but not so much that 
you can't actually play low frequency notes.

-Dan



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