Re: 1kHz 130dB distortion sinewave oscillator.

On 31/01/2025 5:47 am, Edward Rawde wrote:

Approaching 130dB now. Any suggestions for improvement?
It wouldn't be hard to add another four rectifier phases but then I'd have more components than Bill.

But at least I know what mine are doing.

This circuit was simulated in LTSpice 24.1.1 with all component updates as of 30th January 2025.
 Take a sample near 20s and FFT on current zoom extent with Blackman-Harris window.
It's approaching 130dB at 2kHz and approaching 140dB everywhere else.
 I do not know why C13/R28 and similar are needed but without them the simulation speed goes down to us/s
It appears that LT1115 doesn't like being simulated with very little load on its output.
Whether or not that's true in reality I've no idea and it may not be the case in earlier versions of LTSpice.
 Simulation speed in 24.1.1 appears to be about twice as fast as earlier versions for this circuit.

This is a strange circuit. One problem with using an N-channel junction fet like J113 is that if you bias the gate at a higher voltage than the source or drain, it acts as a diode and feeds current into the channel.
I've downloaded and run the second version of the simulation, and the gate doesn't seem to end up more negative than the source or drain.
It takes quite a lot of simulation time before the circuit starts acting as if were an amplitude controlled oscillator, and I'm not interested enough to try and work how it is actually working.
--
Bill Sloman, sydney