Re: High purity 1kHz oscillator

On Thu, 24 Oct 2024 23:19:52 +0100, John R Walliker
<jrwalliker@gmail.com> wrote:

On 24/10/2024 21:56, Liz Tuddenham wrote:

john larkin <jl@glen--canyon.com> 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. Your only
function now seems to be to generate childish insults aimed at most
everyone.
>
Here's some C-V notes. Series AC-coupling caps, or caps used in
filters, can introduce distortion too.
>
https://www.dropbox.com/scl/fo/akiyipqep6n67glfjhcea/ACfQ6By9LRZPKey4tgvpd
DE?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.
>
One could make a parametric amplifier using cap C-V effect.

 
Some ceramic caps make rather poor-quality contact microphones, so don't
use them in audio pre-amps.
 
 

... but COG/NPO ceramics are very well suited to this application.
>
John

They tend to be small values. We use one 10 nF part. Digikey offers a
0.88 uF C0G for $29. Each!

I had some N4700s cooked up special, to temperature compensate an LC
oscillator.