[sdiy] vco question

[harrybissell]

Howdy Jack.

1) why the 'phase shift oscillator'   Do you want a sine wave ?  Easier to build
a sawtooth core VCO, make a triangle and then a sine wave from that. Or a triangle
core VCO and a sine wave from that.

Phase shift oscillator needs three voltage controlled elements. The VCO cores
I mentioned require only one... which can be as simple as a voltage controlled
current source (two transistors).

Sounds like you want an 'envelope follower' as well. For a simple design see Ray
Wilson's interface for the Sound Lab (to guitar).  For the real shizzle try
EDN Magazine Design Idea "Envelope Follower combines fast response, lowest ripple"
by Harry Bissell (zats me :^).  This is a complex circuitat outperforms the fulkl wave
averaging systems, or the Peak Detect (like Ray's circuit) at the expense of being
COMPLEX.

It sounds like you can doi what you want to... I do not fully understand what you want the outcome to
be. Maybe explain what you think your effect might sound like, or how
you would play it

H^) harry

Jackson LaRose wrote:

> hello, my name is jack and i have some questions regarding an RC phase shift oscillator i was hoping
> to build.  i wanted to use a JFET as sort of a voltage controlled resistor in the phase shift
> network to control the frequency of oscillations.  i was going to use instruments (mainly a bass
> guitar)run through an RC high pass filter as the JFET's control voltage. The problem with this is
> that i think the amplitude of the signal (how hard or soft i hit the strings of the bass)will also
> cause frequency fluctuations in the oscillator that don't relate to the notes being played.  I was
> thinking of using another JFET to make a voltage controlled voltage divider before the high pass
> filter to keep the amplitude of the control signal constant while maintaining the frequencies to
> allow the high pass filter to develop the voltages needed to control the FET in the RC phase shift
> network.  Will this work?  If not, is there any way to do this? I was trying to obtain all the parts
> i needed from radio shack, so ive cancelled out varactors or even P-channel JFETs, but perhaps
> something i'm missing using zeners? i'm fairly new to the field of electronics so i'm sure there is
> some trick out there i'm just missing out on
>                                                             -Thank You,
>                                                               Jack
>
>
>
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