Keithley 2015 thd or HP 8903 or ??? - Page 1
Forum section: electronics / testgear

author: FriedMule
author_rank: Frequent Contributor
timestamp: April 28, 2019, 06:59:36 am
content: Thinking about getting some extra gear:-)I want to measure audio amplifiers, DIY and repair but can't decide which unit to choose.Keithley 2015 thd and HP 8903 is old but good gear to a great price but are they to old for today's usage?What are the difference in functions between Keithley 2015 thd and the HP 8903?

author: exe
author_rank: Unknown
timestamp: April 28, 2019, 07:13:04 am
content: People say THD feature on K2015 is a gimmick. It works, but performance is poor. There is much better gear on the market for the job (e.g., a good audio card). Don't take my work, do research

author: jpb
author_rank: Super Contributor
timestamp: April 28, 2019, 12:08:31 pm
content: Quote from: exe on April 28, 2019, 07:13:04 amI have a 2015 and the THD does work but I agree, it is not accurate enough to measure high end audio gear. It is perhaps a little harsh to describe it as a gimmick but I think perhaps it was aimed at auto-testing of products where the audio was not aimed at the hi-fi market.Also, I've noticed that the 2015 prices on e-bay are rather high at present. I paid £250 for mine and then spent some money on re-capping it and so on. It is a good meter as a 6 1/2 digit meter but if you want audio measurements something like the Q401 :https://quantasylum.com/products/qa401-audio-analyzeror software plus an audio interface or sound card would be better.

author: wn1fju
author_rank: Frequent Contributor
timestamp: April 28, 2019, 01:09:12 pm
content: I have both the Keithley 2015 and the HP 8903. Get the 8903. For distortion measurements, comparing the 8903 to the 2015 is like comparing aFerrari to a Fiat.

author: FriedMule
author_rank: Frequent Contributor
timestamp: April 28, 2019, 06:46:34 pm
content: Okay 2015 is forgotten! :-)But is a old HP 8903 better then a newer for about the same money?Any new one's that are worth looking at?EDIT: Oops forgot to say that I know that the computer can do wary great measurements for audio and more, but I have to admit that I'd rather have a dedicated box with dails and buttons then an "end all do all laptop". It's like I feel that a book is fare more satisfying to read from, then a PDA. I know that it is old school. :-)

author: 2N3055
author_rank: Super Contributor
timestamp: April 28, 2019, 07:30:21 pm
content: Well it all depends whether you want to buy nice boxes and look at them all proud (nothing wrong with that..) or want to measure audio equipment.Q401 that jpb mentioned has cca. 25dB lower noise and distortion floor. It is superior instrument. Any pretty much ANY built in sound card in a PC is much better than HP 8903. That can be used with some free or low cost software.Q401 has one nice feature too in that it has built in attenuators so it is safe to connect to power amp outputs directly. And they seem to update software continuously...Regards

author: FriedMule
author_rank: Frequent Contributor
timestamp: April 28, 2019, 09:51:59 pm
content: LOL great reply:-)My laptop has a small headphone jack and that's about all.I'd rather have an electronic lab then a virtual on my pc. I feel that part of the fun is to use the gear and tweek the best out of it, rather then point and click with a mouse.

author: 2N3055
author_rank: Super Contributor
timestamp: April 28, 2019, 10:02:01 pm
content: Quote from: FriedMule on April 28, 2019, 09:51:59 pmAs I said nothing wrong with that ..Have fun.Regards

author: macboy
author_rank: Super Contributor
timestamp: April 30, 2019, 01:29:57 am
content: Actually the distortion measurement of the K2015 is not too shabby, but the internal oscillator/generator is downright poor. That means that to get the best out of this instrument you must have another extremely low distortion oscillator.The 8903 series are very nice. The 8903A is older, and I'd recommend the 8903B. The 8903E (more rare) is the analyzer only, without the generator. You probably don't want that. Again, it is the generator that lets this unit down, though it isn't terrible like the one in the K2015. With the internal generator, you can get down to at best about 0.0020% THD+N at 30 kHz bandwidth (output to input looped, at 1 kHz). With a separate very low distortion oscillator, my 8903B was able to measure down to about 0.0006% THD+N (6 PPM).I sold my 8903B and now use a Panasonic (or National) VP-7722A. This is very similar in operation to the 8903B with a few improvements, like two inputs (stereo) and IMD measurement in addition to THD. It can also display the individual 2nd, 3rd, 4th and 5th harmonic levels. The best THD measurement floor of this instrument with output looped to input is ~0.00008% (< 1 PPM!), and THD+N is around 0.00025%, which is plenty good enough to measure even the best power amplifiers at any power level. If you can find one of these at a good price, I'd highly recommend it. Note that later replacements like VP-7723 etc do not perform as well.Either the 8903B or VP-7722A, as well as many other similar analog instruments also make excellent AC millivoltmeters. Either can resolve down some microvolts AC, reading True RMS (or average-responding if desired). A good use for this is to directly measure noise on power supplies. They also employ reciprocal frequency counters, so they can give fast measurement of low frequencies, unlike a gating type counter. These "off-label" uses really bolster their usefulness, which is good, because they are big old boat anchors that need to justify their size and cost.