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4th February 2008, 06:36 PM
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#2 |
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diyAudio Member
Join Date: Jan 2006
Location: Avalon Island
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A THD analyser.
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Just because you can't hear it doesn't mean no one can. |
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4th February 2008, 08:20 PM
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#3 |
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diyAudio Member
Join Date: Sep 2001
Location: Melbourne, Australia
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A triangle waveform generator and a fast CRO for a visual indication
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5th February 2008, 04:46 AM
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#5 | |
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diyAudio Member
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Quote:
The triangle waveform generator is a good idea. And it is easy to build a fairly good one. (Do a search at national.com for "tri-wave generator".) To check linearity, you would want to make sure that vout/vin is constant, for all expected values of vin. Checking linearity with a triangle waveform for vin is easy: If vout is also a triangle shape, the system is linear versus input voltage. But if the rise or fall portion of the output waveform is curved, or worse, then the system is not linear. You would probably want to check that that is also true when vin is changing, for all expected rates of change of vin. The triangle generator would also handle that, if it had variable frequency as well as amplitude. |
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5th February 2008, 11:45 AM
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#6 |
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diyAudio Member
Join Date: Aug 2002
Location: Germany
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Hi,
interesting topic! What is the ballpark of THD-N when the triangle-wave is visible deformend? Rüdiger
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"I can feel what's going on inside a piece of electronic equipment. I have a sense that I know what's going on inside the transistors." Robert Moog |
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5th February 2008, 12:30 PM
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#7 | |
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diyAudio Member
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Quote:
That's a difficult one, as a perfect triangle is a sine wave + 30% 2nd harmonic. Plus 4th, plus 6th, plus....  .Just as a perfect square wave is a sine wave + 30% 3rd harmonic. Plus 5th, + 7th + ... That is why a tringle is a very crude way to guesstimate linearity. Jan Didden
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/Another new issue: Linear Audio Volume 3! |
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5th February 2008, 12:38 PM
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#8 |
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diyAudio Member
Join Date: Apr 2002
Location: Prague, Kitakyushu, Fukuoka
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Should be said that depending on repetition frequency, the triangle may be distorted in shape, as no audio circuit works from DC to infinity. HF corner results in triangle corner rounding, LF corner results in a "bow" shape of triangle. It will work only for repetition freq. in the midband.
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5th February 2008, 12:50 PM
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#9 |
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diyAudio Member
Join Date: Jul 2005
Location: NW England
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Is the triangle trace any better than the classical XY trace of I/P - O/P sinewave. Loss of linearity is immediately apparent by curvature of the (ideally) straight line at midband, or lack of ellipticity elsewhere (and shows phase to boot!)
This is how I try to detect slew rate limiting. Does that make sense? Brian. |
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Linearity
