Measuring Distortion with a HP 339A and a Keithley 2015 THD

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 analyser, I bought it because of the distortion analyser 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.

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

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.

Thanks for watching.

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5 thoughts on “Measuring Distortion with a HP 339A and a Keithley 2015 THD

  1. I just wondering whether or not to but one of these on ebay today for £320 (2015) to test a HiFi tube amplifier I am in the process of designing…

    Then I found your video, and it answered my question, that yes it can measure an audio amps THD at the push of a button, and so I bought the meter which should arrive soon.

    Many thanks


    • Hi Peter, glad you found the video of some use. The guy I bought mine from (kjds_stuff) has quite a few of them for sale on e-bay, I would say if you are into audio amps and want to measure distortion this is a pretty good meter to do it with. Gerry

        • Hi Gerry,

          I’m not sure you’re correct there. I don’t think THD analysis is an option for the 2015 and 2016, it’s always present. A 2015 without THD is a 2000. Great videos, thanks for making them!


          • Hi Anton,

            Yeah you could be right having just googled again, I was convinced I had seen it as an option – perhaps it was late :) Thanks for the comment


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