Re: opamp sine wave oscillator

On Feb 5, 7:41 am, John Devereux <jdREM...@xxxxxxxxxxxxxxxxxx> wrote:
Inventor <Inventor...@xxxxxxxxxxx> writes:
On Feb 5, 6:33 am, John Devereux <jdREM...@xxxxxxxxxxxxxxxxxx> wrote:
Inventor <Inventor...@xxxxxxxxxxx> writes:

[...]

Well, then maybe the circuit is not for you. You know, I am really
quite surprised at all the negativity in these responses. I figured
out something interesting, I wrote it up, and I posted it on the web
for you to enjoy. I'm not asking for anything from anyone other than
a plain, simple peer review and I've gotten some of that, thank you
very much. The circuit might prove very useful, it might not. I had
fun with the process of discovery so it was a pleasant, positive
experience for me. Why don't we all play nice for a change?
Thanks!

I thought your article itself was quite interesting, nicely laid out
too. I think some people are having a problem with your perceived
claim to "inventing" something new. These circuit arrangements are no
doubt obvous and well known for decades, to those here more
experienced. And for the stated goal of a sine wave oscillator there
are better solutions.

Well, I can't really be certain, but I kind of thought there was
something new here, yes. I thought that stuff about using the inverse
dual voltage divider on opposite sides of the circuit was new, the
fact that it's a whole family of oscillators not just one was new, and
features like the amplitude stabilization and amplitude modulation
were new as well. I think people are reminded of familiar circuits by
the new circuit, and then they reply: "that's been done before!", but
at this point I'm still thinking there is novelty here. If it's an
old familiar circuit, would someone please post a reference, perhaps
an existing web link?

Well you could be right - I am not an expert - but some of the people
commenting *are*.

I don't see that your amplitude stabilisation can work as
advertised. You initially claim to replace the "light bulb"
stabilisation by putting part of the network in the negative feedback
path. But all you are doing is rearranging the network, the overall
effect is the same as far as I can see. You are still left with a
system that requires a slight positive gain to startup reliably, which
will inevitably lead to clipping in the steady state condition.

Any feedback mechanism that operates at the level of a single cycle
will create distortion or require impossibly accurate matching. That
is why the classic "light bulb" is used, it has a relatively long
thermal time constant so as to *gradually* adjust the amplitude over
hundreds of cycles.

And in fact I see you show this with your test results.

--

John Devereux

Yes, that is an interesting question. I also do not quite see how the
amplitude is stabilized by this circuit. I think it is simply
clipping at the peaks. There's not all that much I can do with that
old scope in the photo, but one thing I did was I looked at the peak
on all three waveforms: Vo, V-, and V+. I noticed that during the
distortion V- was not equal to V+, so as expected the circuit is not
in the linear mode during the peak distortion interval. Then, sure
enough, after the peak distortion interval, the circuit transitions
into the linear mode where V- = V+.

Another observation about this behavior is the distortion that occurs
while amplitude modulating. In this case, the distortion appears at
only one of the peaks, while the other peak is left smooth (and it is
more pronounced). I am thinking that this is because under amplitude
modulation, the amplitude clipping occurs on only one side of the
waveform.

But really, I think it will take one of those experts to explain it
properly.
.

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