AW: What are you doing with noise?

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Mon May 13 20:00:00 CEST 1996


>>BTW, another nice thing is what I have seen in a BUCHLA
>>"source of incertainty" (sp?). Buchla uses prefiltered noise and
>>feeds it int  a 1st-order PLL before it is used for S&H stuff !!!
>
>Now *this* picqued my interest.  What sort of basic noise generation
>circuit does the Buchla use?
>
>I am designing a VCO driven shift register type.  To add a PLL sounds
>really interesting.  If the Buchla uses this technique, do you know how
>many flops?  I can see that one could use the raw noise from the
>register, or the output of the PLL's VCO or even the PLL's demodulated
>output or combinations thereof.  Quite interesting.  I just happen to
>have a tube of CD4046 ICs.

The Buchla uses zener noise, a lot of filtering, and this 1st-order PLL.
You don't really need a 4046 for a 1st order PLL. Just build a integrator/
schmitt-trigger oscillator (the way you build cheap LFOs), and feed
the input signal into the inegrator with an additional resistor.
If you write down the equations for the switching times of the schmitt-
trigger, you see that this little circuit behaves just as if it were a VCO
plus an exor-type phase discriminator (1st order PLL, without loop
filter).

JH. 



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