Variable Sine Wave Generator Design

[audioguru]

How can you say that? R6 in series with two paralled diodes provides the nonlinear resistance needed to control the output.

Sorry, I didn't see the diodes.

A sinewave oscillator is not supposed to have distortion. The diodes cause distortion.
A Wien bridge oscillator with an ordinary old light bulb for stabilization of its output amplitude has very low distortion and some that use a Jfet also have very low distortion.

 

[Ratchit]

audioguru,

A sinewave oscillator is not supposed to have distortion. The diodes cause distortion.
A Wien bridge oscillator with an ordinary old light bulb for stabilization of its output amplitude has very low distortion and some that use a Jfet also have very low distortion.

Some schemes work better than others for controlling excess amplification. And of course, the closer you can adjust the R6 to just a little excess amplification, the less the diodes have to vary their conduction current and thereby cause distortion. Anyway, it looks to me like the circuit can be modified to use some other form of feedback control if desired. The main feature of this circuit is a Wien bridge with single resistor tuning.

Ratch

 

[Dean Huster]

The ICL8038 is obsolete and the MAX038 is also not made anymore.

Which is why I usually order several at a time (8038) and get as many engineering samples as possible for pricey chips (MAX038). Then, in my retirement among all my digital and analog devices (and no processors), I have all sorts of things to play with when I didn't have time when I was younger.

 

[audioguru]

The factory that made the MAX038 was destroyed in a monsoon storm.

 

[diy didi]

Here is the one I built. It produces a square, triangle, and low-distortion sine wave. It will run from a few hertz to nearly 1MHZ. If you replace the 555 with a fast comparator circuit, you might make 2MHZ.

Hi there BrownOut. Did you build this for your bench? Does it work nice? What are the two voltage sources in the schematic? Is it a dual supply?

 

[Jaguarjoe]

If you want an 8038, contact me off list, I can help you.

 

[Jaguarjoe]

If you use a lamp stabilized bridge, you might have thermal problems because the ambient temperature will affect the lamp's temperature which in turn affects its resistance etc etc. If your ambient is pretty much always the same you'll probably be OK.

I saw one scheme where the output of the bridge was rectified, buffered, filtered and fed back to the lamp to maintain amplitude stability.