Re: Random thoughts on sinewave oscillators

On Fri, 18 Oct 2024 17:04:15 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

On Fri, 18 Oct 2024 08:36:15 -0700, john larkin wrote:
>

On Fri, 18 Oct 2024 09:48:17 +0100, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
 

Edward Rawde <invalid@invalid.invalid> 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?
 
Ignore the wild decoupling, it took me long enough to get the concept
to work at all.
 
I'm aware that a single package containing two op amps could probably
do a much better job.

>
if noise is more important than waveform, I found amplitude control by
clipping gave the lowest noise.  The oscillators in this...
>
<http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
>
...are amplitude stabilised by clipping.

 
If the gain of an oscillator loop is close to 1.00, say 0.98 to 1.02,
one can add in a small tweak, a crude multiplier or even a clipper, to
make up the difference.
 
Of course, with many-bit DACs being cheap nowadays, it's easier to do a
DDS sine wave generator, and get super-precise frequency and amplitude.
A 70 cent uP can do that, and even use PWM to eliminate the DAC.
 
All sorts of elegant analog circuits are blown away by cheap digital
junk. Sigh.

>
Put the output you get from that through a spectrum analyzer and it won't
look quite so super-duper.

Of course a DDS needs a post-DAC lowpass filter, but a 16 or 20 bit
DAC can make extremely good sine waves.

Just don't push the Nyquist rate.