THD meter circuit needed

[René Schmitz]

Hi!

There is a circuit on Steve Benchs website, which can probably used.
http://members.aol.com/sbench101/
Its at the very bottom of the page. Lots of interesting tube content there
as well!

It uses a notch filter, so that you don't need a low THD source for the
measurement. But I don't know if you can measure as low as 0.005% with it.

Bye,
 René

At 23:36 05.08.00 +0200, you wrote:
>Hello anyone!
>
>
>Does someone of you know a circuit to build a simple THD meter, which
>can measure THD as low as about 0.005%?
>
>The equipment I have:
>-2 channel oscilloscope
>-1 digital volt meter
>-a lot of electronics experience
>
>I propose a such circuit:
>Feed a 1kHz signal into the circuit to be tested, then run the output of
>this circuit into
>a highpass filter, which filters out the 1kHz fundamental, and the
>measure the remaning voltage.
>
>1kHz sine wave ======> circuit to be tested ========> Highpass Filter
>(1kHz cut-off) ======> harmonics which can be measured
>
>
>Is it possible to measure the THD with a such circuit, if a pure
>sinewave and good Op-Amps are used?
>
>The problem is, that I don't have the money to buy a commercial audio
>precision analyzer or a THD meter.
>
>
>Many thanks for any help,
>Alex
>
>
-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159