TTT099 Analog Discovery 2 HiFi Amp Testing

Using an Analog Discovery 2 from Digilent to test Hi-Fi amplifiers. Also the Sencore PA-81 Analyzer is used for comparison and as a dummy load for the measurements.

[@charleslauter5035]

I understand. I had a great McIntosh years ago. At the time there were lot of arguing about tube amps vers. Transistor amps. The matter of phase distortion was big topic. Too bad that we did not have this kind of test equipment back then. Thanks for the post and the reply.

[@tomtektest8042]

I had a professor in EE tell me (in the 1970's) that he could build a FET amplifier that was indistinguishable from a tube amp as long as he used output transformers instead of direct or capacitor coupling. Knowing what I do about him and his accomplishments (he was also one of the best EE Professors I ever had) I believe him. According to him a lot of the "tube sound" was really magnetic saturation in the core of the output transformer. He was a big tube amplifier guy (I think he owned a couple of McIntosh"s, and a Harmon Kardon so I don't think he was biased either way. I don't know if he ever built one but it would be interesting to see.

[@gkdresden]

Hm, is harmonic distortion usually measured for 0 dB(V) or an output voltage of 1 V? I thought that the THD specification relates to it's maximum specified RMS output power. I was also surpriced by the low frequency roll-off of significantly more than 3 dB at allready 100 Hz. Is this an industrial safety mean to protect the speakers or a sign of too rigid capacity coupling at the amplifiers inputs or outputs? Also the phase behavior is very strange. Could you please comment on that?

[@ntoobe]

Nice vid! I wish you commented the results obtained with AD2 in comparison with Sencore (other than power), how accurate is network analyzer and FFT

[@tomtektest8042]

Look for some videos to come using the AD with the Sencore PA81 analyzer. They have complementary features and are best used together as you will see. Also some exciting new software that enhances the use of the AD in Amp Testing.

[@rogeronslow1498]

The Analog discovery is an excellent little instrument but I would tend to believe the Sencore. Also, before I do a harmonic test of any amplifier I first check that the source has a harmonic distortion at least 10dB less than the amplifier under test. Same thing if I do a two-tone test. I also bet that the Sencore 1khz reference oscillator has a much lower harmonic content than the Analog Discovery frequency reference.

[@avejst]

Thanks for sharing :-)

[@ElPasoTubeAmps]

Nice videos on using Analog Discovery. I was considering making a video on a PC based audio analysis system but I think you have already taken care of that, so for now, I believe I will make reference to your videos and not get into that project. I will ask if you know of any freeware oscilloscope programs that are worth downloading that would use the channels of the sound card for input? What I have found so far is really very bad. If I do make a video on a PC audio analysis system, I want it to be based on as much freeware software and existing hardware already in the laptop PC as possible. It has got to be basically "free" and, I also, respect and abide by copyright laws concerning intellectual property.

[@tomtektest8042]

I encourage you to add another perspective. I enjoy your videos and always learn something from them so I think another viewpoint would be good. You probably are already aware that Blueglow Electronics is doing some work with the AD2 in HiFi testing as well. Also please check out the software from The Stuff Made - I think it is very good.

[@charleslauter5035]

With this ANALOG DISCOVERY perhaps you could show the difference between a good tube amplifier and a good transistor amplifier. The phase distortion will tell a lot.

[@tomtektest8042]

I would like to do that since I have a fondness for anything made with tubes but, unfortunately I do not have a good tube amp. That is why I used two transistor amps (Panasonic and Sony). I once had a very good Fisher tube amp, but, due to financial circumstances (I needed money to finish my BSEE) I sold it along with a good tuner and reel-to-reel tape deck. Maybe someday I will get another tube amp but in the meantime I watch El Paso Tube Amps and drool.

[@d942yd42]

I saw another video of someone who specifically mentioned the inaccuracy (that you see) using the AD2 AC Volts reading. I see you suspect your old equipment, where he immediately suspected the AD2.

[@antoespiga]

AFAIK There was a problem with AC voltage reading in the waveforms software, but it was fixed some time ago.

[@musicstevecom]

@@antoespiga That's one reason I selected the Analog Discovery 2, I think its a expanding company and will also update their software.

[@GameProgrammer79]

Liked this video as I am planning for my audio project .. I am very much interested in the amplifier compensation for perceived loudness (link below) en.wikipedia.org/wiki/Equal-loudness_contour Secondly I am really interested in PCM to PWM processors as now a days most of the audio sources are Digital PCM. Amplification of digital sources can be done by either first converting to analogue at very low power level followed by a conventional power stage (class AB, D or hybrid of these two) or the more recent Direct Digital Amplifier. The later uses PCM to PWM converter that gets amplified by power MOSFETs. I wonder if you can do some projects on PCM to PWM processors (many off the self processors from TI are available) and PWM to Analogue conversion .. that will be really interesting project a leading edge highfi .. probably you may prepare a solution and commercialize that by selling it to electronics companies or even a niche one man audio hi if company. Now a days raising funds are not difficult as there are many crowd funding sites (ex: indigogo) that provide a fundraising platform.

[@tomtektest8042]

I don't know a lot about the equal-loudness topic but from the link you provided I think the network analyzer function of the Analog Discovery would be very useful in testing the required frequency response. Let me know how it turns out, or, even better, post a video about it.

[@TheStuffMade]

Some time ago I wrote an Audio Analyzer Suite for Analog Discovery, it might be of interest to you, it's completely free and you can find the downloads and me demonstrating it in a few videos on my youtube.

[@tomtektest8042]

Thanks. I will take a look at your videos on KZbin.

[@TheStuffMade]

Great, it's no replacement for one of the high end Audio Precision instruments, but more a cheap way of getting the same features at a low cost and probably comparable in performance to the classic audio analyzers from HP, Tektronix etc.

[@tomtektest8042]

I have downloaded the Suite to a Windows 7 computer with the Analog Discovery 1 and I look forward to trying it. First, I will read the Help file. Thank you for letting me know about this and for developing and releasing it.

[@TheStuffMade]

Thanks, let me know if it's useful and if you find any bugs or any features you would like to see added. I've got another project for Analog Discovery you might find interesting, it's a fairly ambitious impedance analyzer project I've put quite a lot of work into so far.

[@tomtektest8042]

Is it possible to send you e-mail directly?

[@gregd6022]

Well that's one terrible amplifier... ;) (but yeah as mentioned in another comment, you don't do a "control" test, so you have an inherent methodology issue, but i do realize this is amateur hobby stuff).