Re: Low distortion sinewave oscillator without big capacitor.

On 9/04/2025 3:18 am, john larkin wrote:

On Sat, 5 Apr 2025 10:15:27 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
 

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsqeh2$1emr4$1@dont-email.me...

On 5/04/2025 1:48 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vsq3um$107nb$1@dont-email.me...

On 5/04/2025 5:32 am, john larkin wrote:

On Fri, 04 Apr 2025 18:03:19 +0100, Cursitor Doom <cd@notformail.com>
wrote:
>

On Thu, 03 Apr 2025 13:08:20 -0700, john larkin <jl@glen--canyon.com>
wrote:
>

On Fri, 4 Apr 2025 05:14:44 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
>

On 4/04/2025 4:02 am, john larkin wrote:

On Sun, 30 Mar 2025 14:54:56 -0400, "Edward Rawde"
<invalid@invalid.invalid> 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.
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What I have so far is below.
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Any comments?

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Suppose you built an oscillator and had a switch that varied the loop
gain between 0.98 and 1.02. Now measure the amplitude of N cycles and
flip the switch if it's too high or too low. Switch at the zero
crossing.
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I wonder what distortion would be like.

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Why not measure it? LTSpice could probably give you a sine wave whose
amplitude ramped up linearly for a bit, and ramped back down again.
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Do a DFT on that and you'd have your answer. It wouldn't be good.
>

(I wouldn't really do that. It's just an idea to play with.)

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Only if you don't know what you are talking about.

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An idea is like a cute baby puppy. Some people want to feed it and
play with it and some people want to club it to death.

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"Please don't feed the troll."

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The point here is that some people, especially fatheads with advanced
degrees, are incapable of having ideas, and react by being hostile to
ideas and to people who have them.

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I've got my name three patents, so I'm demonstrably capable of having ideas.
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I am hostile to people who tout bad ideas.

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Don't you think it would be better to just explain why you think an idea is bad Bill?

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I usually do.
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And also, if necessary, to just explain how and why you think it should be done.

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I have been known to do that. You should know - I've done it to you, here, and I'm about to do it to John May whom I really like
and approve of.
>

Being hostile doesn't make you look good and it does the opposite of persuading others that their ideas are bad.

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Few people can ever be persuaded that their ideas are bad. John Larkin definitely isn't one of them.
>

So why be hostile at all?

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The same mechanism that persuades people that their bad ideas aren't too bad allows them to gloss over any criticism that isn't
thoroughly explicit.

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You can be critical without being hostile.

 He can't. He lives to be nasty.

Not flattering John Larkin is being nasty, from John Larkin's point of view.

The super low distortion oscillator thing is just another venue to
call people stupid. It's a Spice-as-game thing, totally unrealistic in
real life.

John May claims to have built and tested some examples. Audiofools do have an interest in very low distortion sine wave sources, so there's a small, but well-heeled market for the product. It's sort of interesting - national measurement labs do go in for that sort of precision.
https://www.amazon.com.au/Coaxial-AC-Bridges-B-Kibble/dp/0852743890
Bryan Kibble worked for the British National Physical Laboratory
https://en.wikipedia.org/wiki/Bryan_Kibble
It was his book that drew my attention to the need for non-progressive windings on toroidal inductors if you wanted zero external field (which matters if you are using a pair of them to measure the conductivity of a not-particularly conductive fluid).
That's a real-life application, if a very specialised one.
--
Bill Sloman, Sydney