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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: 80dB now but still needs improvement at 1KHz
Date: Tue, 19 Nov 2024 16:12:26 +0000
Organization: Poppy Records
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Edward Rawde <invalid@invalid.invalid> wrote:

> "Liz Tuddenham" <liz@poppyrecords.invalid.invalid> wrote in message
> news:1r37pyc.1bodve2fz5t4wN%liz@poppyrecords.invalid.invalid... 
> Edward
> Rawde <invalid@invalid.invalid> wrote: > > [...] >
> >> Now approacing 90dB if you believe the simulation with with this
> >>experimental circuit. > You'll want to find something else to do while
> >>it simulates.
> >> How to inprove it further?
> >
> > At 1 Kc/s, a distortion figure of 90dB represents one cycle in 10^9, so
> > you would have to run it for 1000 seconds before the startup transient
> > became insignificant.
> 
> The startup transient was not included in the FFT but in any case the
> circuit has other issues so here is a circuit which works as intended.
> Harmonics are approaching 100dB down and 1k c/s is below 90dB. Simulate
> overnight then stop. It will be at about 250 seconds. Select roughly the
> last 50 seconds and FFT on current zoom extent. Number of data points may
> need increasing.

The startup transient of the FFT would have to be included, so that may
set a limit to the accuracy of the simulation measurements.  Even if you
start on a zero-axis crossing, you will get spurious results because of
the finite length of the sample.

This can be demonstrated by doing FFT on samples of fewer and fewer
cycles from the middle of an apparently pure sinewave.  As the sample
length decreases, spurious harmonics begin to appear, even though they
don't exist in reality.

[...]
> We could probably have a discussion here about why c/s is better than Hz

I don't know if it is 'better' but it suits me  - and nobody seems to
have any difficulty understanding it.  By using a descriptive term,
rather than a commemorative one, beginners find it easier to understand
as it sounds less like jargon intended to exclude the uninitiated.

(I have nothing against H.Hertz, it's just the principle that worries
me).


> Version 4
> SHEET 1 2196 932
> WIRE -64 -576 -96 -576
> WIRE 48 -576 16 -576
>
[...]

I don't use Spice, so the rest doesn't convey anything to me.


-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk