Re: Random thoughts on sinewave oscillators

"piglet" <erichpwagner@hotmail.com> wrote in message news:ver5b2$2p6tm$1@dont-email.me...

On 17/10/2024 12:32 pm, piglet wrote:

On 16/10/2024 9:55 pm, Edward Rawde wrote:

Is the reason why this doesn't produce a better looking sinewave because the amplifier slew rate is faster going down than it is
going up or some other reason?
>

...

>
>

>

Thank you for taking the time to look at this piglet.

I assume this is an intellectual challenge and not a real project?

Yes I'm not likely to be building it any time soon.
There was talk of sinewave oscillators here recently so I decided to see how easy or difficult it would be to make a sinewave
oscillator without using lamps or thermistors.
I think it might be easier if I used standard op amps.

I  suspect the jfet gate-channel is forward biased so the amplitude control section is my first place to look?
>
piglet
>

>
Hmm, that forward biased gate only happens during startup. Some other ideas:
>
The amp input bias R6 loads the Wien network too much - try lowering the Wien network impedance?

It has been lowered in the circuit below.

>
Replace R7 with constant current sink if you think slew rate is the issue?

Done

>
Rectifier load is too heavy on the follower - increase R22?

Added separate follower.

When trying other suggestions, it's hard to get a stable amplitude control loop.

The circuit below produces a reasonable looking sinewave but the rise time still seems to be slower than the fall time.
It may be that the amplifier in use is not ideal for this.

>
Q5 base reference is not stiff enough - lower R26-27-28?
>
Q4 base current flows through rectifier - reference D1 instead to +12 rail?
>
Maybe later I will find time to explore...
>
piglet
>

Circuit version 2 follows.

Version 4
SHEET 1 2888 1280
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TEXT -424 800 Left 2 !.tran 0 100 0 0.0001
TEXT 632 -200 Left 3 ;Edward Rawde's weird sinewave oscillator. V2. October 2024