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From: John R Walliker <jrwalliker@gmail.com>
Newsgroups: sci.electronics.design
Subject: Re: High purity 1kHz oscillator
Date: Thu, 24 Oct 2024 23:19:52 +0100
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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