Distortion Meter

[pandaemonium]

Anyone know where I might find a schematic for a half-decent distortion meter? I found a few tube types, but the dinosaurs broke all my tubes when they where running away from that big damned meteor!

 

[Nigel Goodwin]

Anyone know where I might find a schematic for a half-decent distortion meter? I found a few tube types, but the dinosaurs broke all my tubes when they where running away from that big damned meteor!

I'm sure a simple google will find you some, but for a start have a look here **broken link removed**.

 

[Dean Huster]

It's not often that you really need a THD analyzer with all the bells and whistles. If you need cheap, simple THD measurement, you can build an active notch filter that'll do the job. I've build notch filters and low-distortion oscillators that are capable of 0.01% distortion measurements or less. They're single frequency, but usually all you need for specifications is one, two or at most three standard frequencies. The notch filter is slightly tuneable to allow for slightly off oscillator frequencies, or oscillators that use wirewound pots for their variable adjustment that tend to have "jumps" as they're adjusted.

With the small, easy-to-make ciruits, you can make good THD measurements for less than $20 per frequency or next-to-nothing if you have a good stock of common parts.

The key to it all is having a decent ac voltmeter .... not just a multimeter with an ACV range. An ac voltmeter has ranges that allow precise measurement down into the millivolt/microvolt ranges.

Dean