On Wed, 20 Feb 2002, Harold M Hallikainen wrote:

>         Well, you could go with a Wein Bridge oscillator. It consists of a
> non-inverting amplifier with a gain of three (generally made with an op
> amp and a couple resistors), a series RC from the output to the input,
> and a parallel RC from the input to ground. At 1/(2piRC), the "gain" of
> the series/parallel network is 1/3 at an angle of 0 degrees. Make up the
> gain with the amplifier and it oscillates. You can put a small light bulb
> in place of the resistor between the inverting op amp input and ground go
> get automatic gain control. As the signal gets larger, the lamp current
> goes up, increasing resistance and decreasing gain). The lamp probably
> won't work at real low frequencies (it will follow the waveform).

  Or, as I tell you before, a n-fet as controlled resistor, drain to
inverting , source at ground. A small signal diode ( better germanium, but
works also with 1N4148 ) will rectify the output sinusoidal signal and
drive the gate respecting the polarity command voltage through a
potentiometer, small filtering cap to gnd.
 A series resistor with drain is required and also may be necessary a
parallel resistor with d-s fet circuit to adjust the gain. Is the best
and stable way from 0.1Hz to 100KHz sinusoidal oscillation, better than
any other solution ( from distorsion performances speacking ) including
8038/max038 family.

best, Vasile

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