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-   -   how to clean fixed frequency sine wave ? (http://www.diyaudio.com/forums/parts/24222-how-clean-fixed-frequency-sine-wave.html)

Bernhard 14th December 2003 12:44 PM

how to clean fixed frequency sine wave ?
 
Hi,

for distortion measurement I like to have a very clean sine of 10kHz.

Is it possible to filter the sine so that undesired distortions are attenuated to nothing ?

Is there a ready-to-build filter somewhere in the net ?

Thanks, Bernhard


My email notification on replies does not work any more :(

OliverD 14th December 2003 12:58 PM

As opposed to other wave forms, a sine wave of 10 kHz does not contain any signal at a frequency other than 10 kHz.

That means, in theory you will get rid of all noise and distortion if you have an ideal band pass filter designed for 10 kHz. In the real world, however, this filter will be far from ideal, but still it will the dominant contributor to the total noise and distortion.

Steven 14th December 2003 03:00 PM

Use an LC lowpass or bandpass filter with corner or center frequency of 10kHz.

Steven

tschrama 14th December 2003 04:06 PM

Hi Bernard,

I think you need a high Q double T network or something like that... but I have good results with a diy oscilator (0.004% THD).. it's a simple wienbridge with a 3.5 watt/220 lamp and a NE5534 ... it's at 1KHz, but 10KHz should be possible of course, perhaps even with lower distortion...



Goodluck,
Thijs

PS
You can check the www.sound.au.com for the 'feed-forward' oscilator.. maybe you can improve on it.. I've been wanting to do that for some time now but haven't started yet..


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