Re: Low distortion sinewave oscillator without big capacitor.

On 31/03/2025 5:54 am, Edward Rawde wrote:

Not long ago JM posted a 1KHz sinewave oscillator with very low distortion.
It used a 470uF non polarized capacitor which in practice would probably be made from two 1000uF capacitors.
There's nothing wrong with that but I wanted to see whether I could make a working circuit without needing such a large capacitor.
 What I have so far is below.
 Any comments?

It relies on the Analog Devices MAT-02 dual transistor, which is now obsolete
https://www.analog.com/media/en/technical-documentation/obsolete-data-sheets/mat02.pdf
The .asc file shows eight NPN transistors labelled MAT-02, presumably in four pairs of the part, but it isn't clear which of the eight transistors should be paired up.

What's the best way to control the output level?
Currently it's 5v pk-pk but I rather have half that.

The rectified currents from the four phased shifted versions of of the output waveform flow through R13, R14, R15 and R16 into R11 and through it into the virtual earth set up at the inverting input of U3, where the summed current is compared with a fixed current drawn from the +15V rail through D1 and R10.
Doubling R10 from 330k to 680k would roughly halve the output amplitude.
One could be more precise, but it wouudl be hard to justify the extra effort.
--
Bill Sloman, Sydney