[sdiy] quadrature sine wave oscillator question

[Ingo Debus]

Czech Martin wrote:
 > This looks like a state var filter, but the Q
 > regulation is set up so that a sine wave can build
 > up.
 >
 > To prevent heavy saturation and distortion a amplitude
 > regulation is needed, like in all low distortion designs
 > be it Wien bridge or else.
 >
 > Unfortunately the gain/phase characteristics change
 > a lot if the frequency is changed a lot, so
 > the regulator must work fast.
 >
 > Usually this is done via saturation devices (zeners etc.).
 > This will cause some distortion.
 > Or by some peak detector and very slow lowpass filter.

I built one a long time ago. This was from a PMI application note.
Worked well AFAIR...

(dig, dig, dig)

Ha, found it! It's in the datasheet of the DAC-8408. I didn't build it
with digital control like suggested in the application. The regulation
is done with a JFET as VCA, controlled from both the sin and the cos
output.

Ingo