Function_generator

[BrownOut]

Has anyone built a wien-bridge variable frequency oscillator? It requires a dual/ganged vairable resistor. How well does that work?

 

[Warpspeed]

THe circuit works well enough for it to be commonly used in low distortion commercial audio signal generators.

Another (classic) way to stabilise the output amplitude is with a small incandescent light bulb.

Wien-Bridge Oscillator Using Incandescent lamp Stabilizer | Free Circuit Diagram

 

[Roff]

THe circuit works well enough for it to be commonly used in low distortion commercial audio signal generators.

Another (classic) way to stabilise the output amplitude is with a small incandescent light bulb.

Wien-Bridge Oscillator Using Incandescent lamp Stabilizer | Free Circuit Diagram

The lamp will also create (odd harmonic) distortion at low frequencies, the amount being dependent on frequency and the thermal time constant of the filament.

 

[Warpspeed]

Yes, and the amplitude changes with ambient temperature as well.

Nothing wrong with the Wien Bridge circuit, it gives extremely low distortion, lower than just about anything else, which is why it is used in many audio signal generators used for measuring distortion in audio equipment.

There are many methods to stabilise the output amplitude. Lamps and diodes are the simplest, but you could also use a FET or a light dependant resistor, or even an analog multiplier if you wanted.

 

[BrownOut]

The mega-company Hewlett & Packard was built on the Wien Bridge oscillator. Bill or Dave, I forget which now, built and sold them to Disney for sound effects. That started the whole show.