Re: High purity 1kHz oscillator

On 25/10/2024 4:37 am, john larkin wrote:

On Thu, 24 Oct 2024 20:39:03 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
 

On 24/10/2024 4:44 am, john larkin wrote:

On Tue, 22 Oct 2024 01:10:41 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

But I suspect that component tolerances and mismatched FETs will ruin it.

>
The very best bulk metal foil resistors have voltage-resistance
coefficients of a few ppm/volt. Most resistors are much worse.

>
Metal film resistors aren't all that much worse than bulk foil
resistors, and they are pretty cheap aznd widely available.
>

Just the resistors can kill distortion specs.

>
Not that you can cite an example
>

At low frequencies, self-heating and tempco can add distortion too;

>
Pull the other leg.
>

The old HP oscillators
had that effect from the lamp filament.

>
The lamp filaments ran rather hotter.
>

DGMS on capacitor nonlinearity.

The capacitors and resistors would have to remarkably bad to make much
difference to a well-designed Wein bridge.
>
You've already got started on making an ass of yourself about resistor
non-linearities. Making bizarre claims about capacitors is more of the same.

 Gosh, you keep getting nastier and crazier every year.

I'm sure it makes you feel better to think that.

Your only function now seems to be to generate childish insults aimed at most
everyone.

By which you mean that I don't flatter you as fulsomely as you think you deserve.

Here's some C-V notes. Series AC-coupling caps, or caps used in
filters, can introduce distortion too.

You need ceramic caps - with pretty horrible voltage dependent capacitance - to get that. NP100 is roughly as good as mica or polypropylene.

https://www.dropbox.com/scl/fo/akiyipqep6n67glfjhcea/ACfQ6By9LRZPKey4tgvpdDE?rlkey=is0vbs7m6xft5u9as5r8eyp30&dl=0
 It's sort of outrageous that most ceramic cap data sheets specify
capacitance and voltage and hide the fact that you don't get both.
 Film caps can have C-V effects too, and those can matter at PPM
distortion levels.

The 1% tolerance 15nF caps that Edward Rawde would use - if he ever built his Wein bridge - use a polypropylene dielectric film which is remarkably good - better than polycarbonate (which is marginally better than polyester).

One could make a parametric amplifier using cap C-V effect.

But nobody has, certainly not with plastic film capacitors.
You really do seem to be sliding off into senility.
--
Bill Sloman, Sydney