Keithley 2015 vs HP 34401A - Page 1
Forum section: electronics / testgear

author: uoficowboy
author_rank: Regular Contributor
timestamp: January 04, 2014, 03:45:51 pm
content: Hi - I'm thinking of selling my 34401A to get a Keithley 2015. The THD features of the 2015 would be super useful to me. They seem to go for a very similar price on Ebay, so it'd be an almost even trade (minus Ebay's exorbitant fees, of course).Anybody have any feelings on if this is a good or bad idea? I do not think schematics are available for the 2015, while they are available for the 34401A, so that's a bit of a downer.I still need to sit down and do a side by side feature/spec comparison between the two.

author: bingo600
author_rank: Super Contributor
timestamp: January 04, 2014, 05:27:24 pm
content: Keithley told me the 2015 is a K-2000 with a THD board addon.So the DMM measurement engine is a K-2000 , witch has been somewhat reverse engineered.I had the same dillemma , had a 34401A and the 2015 seemed nice.Solution .... Keep the 34401A and get a 2015 also/BingoPs: Make sure the VFD display is bright as in get some picts , mine is a bit weak.

author: bingo600
author_rank: Super Contributor
timestamp: January 04, 2014, 05:30:17 pm
content: Btw: User KJDS here (UK) has K-2015 for saleSometimes he gives a nice rebate to forum users , write him a PM.http://www.ebay.com/itm/Keithley-2015THD-6-5-digit-bench-DMM-multimeter-with-harmonic-analysis-/350968760278/Bingo

author: uoficowboy
author_rank: Regular Contributor
timestamp: January 05, 2014, 04:35:53 pm
content: Quote from: bingo600 on January 04, 2014, 05:27:24 pmThank you for the 2000 schematics! That is great!

author: macboy
author_rank: Super Contributor
timestamp: January 05, 2014, 07:09:39 pm
content: I don't know what you intend to use the THD features for, but be sure to read and understand the specifications of the 2015 THD measurements. The noise and distortion floor is quite high, far too high to measure any kind of consumer or pro audio. It may be useful for telecom audio or other low-fi applications.

author: uoficowboy
author_rank: Regular Contributor
timestamp: January 06, 2014, 02:34:27 pm
content: Quote from: macboy on January 05, 2014, 07:09:39 pmI'm planning on mostly testing consumer audio amplifiers, but also potentially some (non audio) power amplifiers I've been working on.I just picked up an HP 339A on Ebay a few days ago. Hasn't arrived yet - but it should handle most if not all my THD needs. It is way higher end than the 2015, but also more specialized... The 2015 calls out 0.056% residual distortion. So that should be good enough to measure 1% THD, or even 0.1% THD+N methinks. That's all I really need. Of course the 339A can measure below 0.01% THD+N.So the 339A has me covered - but I just wonder if there's some advantage of the 34401A over the 2015 - I mean it's a lot smaller than the 339A and so it'd save me some bench space for when I don't need the super low noise of the 339A...

author: G0HZU
author_rank: Super Contributor
timestamp: January 06, 2014, 10:13:34 pm
content: I've not used the HP339A and I'm not an audio fanatic but I do have a 2015 and I use it now and again for measurements of harmonic distortion. I'm only really interested in harmonic levels down to about -65dBc most of the time.TBH I don't really care about THD as it is a blinkered and misleading thing to measure if it is used as a figure of merit. What is good about the 2015 (over the 339) is that it can measure the levels of all the harmonics and then provide individual harmonic levels. i.e. it can give a profile of the harmonic performance.I think the 339A can only notch out the fundamental and then give THD + Noise.If you were really looking for the best of both worlds I guess you could make an external notch filter or maybe even combine the two instruments. Does the HP339 let you feed the post notch signal to an external meter? eg the 2015?The 2015 is going to be far more versatile than the 339 and can read and display a lot more info a lot faster if you get the data via GPIB. That's how I use mine. I can look at a baseband signal and see and measure all the individual harmonics up to 40kHz in a few seconds. The HP339A can't do this

author: G0HZU
author_rank: Super Contributor
timestamp: January 06, 2014, 10:33:08 pm
content: Here's a link to show how I evaluated the THD function on my 2015 when I first bought it.https://www.eevblog.com/forum/testgear/keithley-2015thd-initial-tests/msg313669/#msg313669Since then I've improved the harmonic analysis software and it has a marker function to allow each harmonic to be measured using the mouse. See below: You simply click on each green bar to measure the level of that harmonic in terms of -dBc.What is so good about the 2015 when used like this is it can auto detect everything so you just stick a signal in and it will give you the Vrms plus it measures and tells you the fundamental frequency plus all the harmonic info and it can do it very quickly.It's certainly good enough for what I needIt would be nice if there was access to raw DSP data over GPIB or even just graphics data to allow a true spectrum analyser display on a PC. Without this the meter is a bit compromised because it just gives harmonic data and not any data about spurious terms that might be there as well.

author: holko
author_rank: Contributor
timestamp: January 06, 2014, 11:24:37 pm
content: For most audio measurement a simple sound card has proven to be quite good.I got the Quad-capture manufactured by Roland.This soundcard is also recommended by the makers of SpectralPlus.http://www.spectraplus.com/Hardware.htm#SoundCardsIt measured 0.003% THD+N in loop back self test.Test report of Quad-Capture-Holko

author: G0HZU
author_rank: Super Contributor
timestamp: January 07, 2014, 12:04:47 am
content: Yes, a sound card can be very powerfulThat SW looks like a modern version of the old Spectralab program. I've got a version of it dated 2000 and it is pretty good. it is also really useful for generating multiple audio tones and also things like DTMF sequences.However, I found it quite limited for my needs partly because I don't have a decent soundcard and also because of the fiddly necessity to calibrate it (or at least try to calibrate it) to suit the soundcard.What I like about the 2015 is I can just stuff a signal into it and check to see if the harmonic levels are acceptable and also measure the level of the signal quite accurately.However, I like the look of the Roland USB (192kHz 24bit) SC interface because it is portable from PC to PC so I am tempted to research/buy something like that to use with my netbook or my main PC.