how to clean fixed frequency sine wave ?

Bernhard · 14th December 2003, 11:44 AM

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, 11:58 AM

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, 02:00 PM

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

Steven

tschrama · 14th December 2003, 03:06 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..

14th December 2003, 11:44 AM	#1
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	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

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14th December 2003, 11:58 AM	#2
OliverD diyAudio Member Join Date: Nov 2002 Location: Germany	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.

14th December 2003, 02:00 PM	#3
Steven diyAudio Member Join Date: Oct 2003 Location: The Netherlands	Use an LC lowpass or bandpass filter with corner or center frequency of 10kHz. Steven

14th December 2003, 03:06 PM	#4
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	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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