Simple THD meter

[EUVL]

These days, with 24 bit sound cards, there is actually little argument for a hardware based THD meter, other than DIY for fun (I did).

You can generate a good sine wave using a sound card, and then add Cordell's distortion magnifier, after which you feed the residual error signal back to the sound card for spectrum analysis.

Even the pro's do it this way these days.


Patrick

 

[xavirom]

Hi WENSAN.
They will be able to get better results with other operational amplifiers?
Thanks

 

[AndrewT]

I told Mr. Pass this idea.
Mr. Pass encouraged me to achieve this idea.

Why after more than 4years is this still in the Pass section of the Forum?

Design & Build
- Equipment & Tools

 

[kasey197]

andrewT, one finds all sorts of pass inspired electronics here that could go into other sections eg phono, line stages etc ...

Separately, whatever happened to wensan ? His stuff was always a very interesting read .......

 

[Nelson Pass]

Yes, I'm sorry that we have lost contact. I met him back in 2010 or so,
and he even built a semi-tester for us.

I hope you are doing well, Wensan.

 

[BrightXA]

If there is a phase difference between point A and point B, is the output THD?
I don't really understand how the circuit works.

 

[Nelson Pass]

No, it doesn't show up as THD. Just phase difference.

 

[BrightXA]

Thanks! Pass
I know, if there's a phase difference from DUT, this circuit can't measure THD.

 

[Nelson Pass]

That would be a problem. It is possible to use a phase shifter to adjust the
relative phase, or in the case of an amplifier you might find that frequency
where it is exactly in phase (or possibly 180 deg out of phase).