[sdiy] Filter Banks & CSound

[Ian Fritz]

JB --

I don't like to put up circuits that appeared in Electronotes, since Bernie 
is still selling back issues.  Here's a link to a transistor phase shift 
oscillator:

http://www.edwinxp.com/carriculam/Experiments/RC%20Phase%20Shift%20Oscillator/RC%20Phase%20Shift%20Oscillator.html

To make a filter I just put a small-resistance trimmer in series with CE.

My circuit uses a low-noise transistor (e.g. 2N5088) and operates between 
+12 and -12 volt rails.  For the biasing resistors I have RB1 = 120k, RB2 = 
33k, RC = 10k and RE = 4.7k. In place of the emitter cap I have 4.7 uF in 
series with a 200R trimmer to set the Q.

The feedback network has R1 = R2 = 68k and R3 = 0.  The caps are C1 = C2 = 
C3 / 2 and are chosed to give the correct frequency.  The frequency comes 
out to about .06 / R1 C1, with f in kHz, R in kOhm and C in mF.

I hope this is enough to give you the general idea.  If I were doing it 
again, I would probably use low noise opamps, but at the time there weren't 
any readily available like there are now.

Let me know if you need more info.

   Ian


At 01:53 PM 12/11/2002, jbv wrote:


>Ian,
>
> > I used a single transistor circuit for my resonators -- just a phase-shift
> > oscillator with a bit of degeneration to set the Q.  I started with nominal
> > Q values around 20, but had to increase this somewhat to get 10 dB contrast
> > with all the bands turned up.  My design has variable amplitude on each
> > filter and variable Q in sub-banks of six frequencies.  That way I can --
> > for example -- do some formant shaping at low frequencies and timber
> > enrichment at high frequencies at the same time.
> >
>
>Do you have any schematics available, at least for 1 band ?
>
>Thanks,
>JB