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Measuring Distortion with a Keithley 2015 THD

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louyueqing
Posts: 2
Joined: January 3rd, 2018, 12:57 am
Country: China

Measuring Distortion with a Keithley 2015 THD

Post by louyueqing » January 3rd, 2018, 1:14 am

I have had my HP 339A for a long time now and despite only using it a small handful of times it is a really great instrument – but – its big and takes up a lot of shelf space. A few weeks back a purchased a Keithley 2015 THD which is a 6.5 digit bench meter with a built in distortion analyzer, I bought it because of the distortion analyzer function. I would like to get some more instrument shelf space back so am able to replace the HP 339 with this 2015THD I will make that much-needed space. I decided to build a simple output circuit so that I can induce some crossover distortion and compare the basic measurements on these two devices to see the results. Now I must make it clear that this is a basic 101 on measuring distortion, I am sure there is a lot more to know that I do but I believe I cover off the basis.

https://youtu.be/sVUXEt0nZ80

The simple drawing I used to explain the test and test circuit.
Image


I will tear down the HP 339A on video to show how nicely these are built. This is one of those rare “all analog” devices that has not digital parts at all, watch out for that video if you like seeing the guts of nicely built equipment.

After this, it’s time to do some THD measurements. I’ve built a couple of nice tube amps with just a DMM, I'm trying to drive my amp MC33941EG(datasheet: http://www.kynix.com/uploadfiles/pdf2286/MC33941EG.pdf) into an appropriate resistive load and measure across that, the amp needs to see the right impedance in order for the distortion measurements to be meaningful.

Thanks for watching.

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