#87 - NAD 3225PE frequency response measurements
Вставка
- Опубліковано 24 лип 2024
- Some ways of measuring frequency response were discussed, and some of them demonstrated.
This channel is also available at lbry.tv/@FeedbackLoop
Repair video: • #86 - NAD 3225PE stere...
Forum: www.eevblog.com/forum/repair/... - Наука та технологія
This is AWESOME. What superb old amplifiers these units are. Thank you very much mate.
Maybe the scope doesn’t do phase unwrapping when it gets to 180-degrees.
I believe I remember this happening when I wrote a script for FRA in Matlab. Keysight 3000 series scope, 33120 f-gen.
Yep, this is what happens
It is also possible that at lower amplitude-levels the phase detection mechanism starts to fail (I have seen this before)
Wonderfully InTeReStInG
HP/Agilent/Keysight and I THANK YOU.
This was a resounding Win Win for your followers 👍😎 Good times.. Good times.
Very interesting, Im very interested in the science of metrology, and very much enjoy this sort of stuff...cheers.
Great education video, thank you for sharing this.
I really like this. I'm a big fan of Python and have a few GPIB instruments that I'd like to control. Good, solid, demonstration, clearly explained. I was debating whether a GPIB-to-USB was worth it. Will go for it.
Very interesting video. I also find the HP 8903A/B to be an excellent piece to test equipment for audio work with a very low THD source. They can be found on eBay for reasonable prices, especially if not working.
You need an Hp8903A/B. Love mine. And A great restore video too!
Thanks for this information, I have the same scope.
That was very cool! So how flat was the measurement of the SigGen on the DMM without the amplifier? I know the DMM has a pretty high cut-off but this might have been interesting too. Could always subtract this from the measured result if it was significant.
There is no limit to perfection. Yes, that is something to consider, and potentially improve the accuracy. Thanks.
@@feedback-loop Haha - didn't mean to be picky. Just thought it might be interesting. Looking forward to your next one and thanks again.
I also had the same question about the flatness of the 33120A output while watching the video. I assume it would be reasonably insignificant compared to the flatness of the amplifier output. Just took a quick look at the 33120A datasheet. The specs are that the sinewave flatness below 100kHz is ±1% (0.1 dB) relative to the 1kHz level.
Silly question: Could you measure THD of the gen and subtract it from the THD in the output?
No, it does not work like this. The higher distortion will completely mask the lower one. It is like measuring, let's say, a -100dBm signal in the presence of -40dBm noise. The signal is way below the noise floor.
What is the frequency response of a small transistor radio?
Hi, I saw the video two times and to be honest It's very difficult to me process all this technical information. I´m looking for a NAD amp, but I see the 3020 model is very popular ; I would like to know if you had the cance to compare it with the 3225 or if you have some opinion about what is better. thank you.
Isn’t it a bit risky hooking the scope earth clip to the amplifier output, in case the amp doesn’t like having the output tied to earth.
Perhaps I should have spent a few moments clarifying this. There is always something you wish to have mentioned after a video is published. I am sure you have the same feeling every once in a while.
You are right, in general this is something to be aware of and to be careful about. In this particular case there is no problem at all. The speaker negative is the same as the common ground for the whole unit.
Perhaps would be great to share python code in text format as well ;) Good vid, thanks.
Attached to my post on EEVBlog forum. Link in the description.
I suspect the bass and treble pots are not electrically centered when they are physically centered! The curves always had those bumps on the ends with the dip in the middle with the controls centered in their detents.
What about using a simple voltage divider in order to bring voltages in check and use a high-end 24-bit computer interface?
I am afraid it is not that easy. There is no such thing as a simple voltage divider if your signal is not DC. There are all sorts of problems such as parasitic capacitance and inductance, so you would need to compensate somehow, which has many challenges. It is tricky to design a truly transparent front-end with flat frequency response, very low distortion, precise attenuation factor and so on.
Take a look at this: www.pmillett.com/ATEST.htm
great video as always.
Can you please make a video showing exactly how to setup and use the agilent 82357B USB-GPIB on Ubuntu with Python?
I am not sure it would be very interesting. Too specific, too technical. Do you have a particular problem or you don't even know where to start? I vaguely remember it was not too difficult, and there is plenty of advice online.
Simply speaking, just download linux-gpib-4.x.x, untar, ./configure, make, sudo make install. Then I recall you need to find some binary firmware for this particular adapter and drop it into some particular directory. Python module is included, just "import gpib" and off you go.
I noticed the link to the eevblog forum does not work, it gives a "404 Not Found" error message. Maybe you could add another link to you Python scripts?
Ops, the last slash was missing. Fixed. Thanks.
Great video. Just one remark: frequency response measurements will only make sense when you are sure the DUT is not producing a significant amount of distorsion. Clipping can be seen easily using an oscilloscope, however slew rate distorsion occurs often unnoticed. If in your automated gpib setup the output is slew rate distorted, you will make a comparison between the rms value of your input sine wave and the rms value of your slew rate distorted output wave form, which can result in a faulty frequency response characteristic. See also: users.skynet.be/hugocoolens/spice/ua741/artikelextended.pdf
No love for gnuplot?
I forgot to mention it. I am not used to it, but it is a great tool as well. There is always more than one way.
I don't know why oscilloscope manufacturers don't put in an audio setting in the menu that brings up all the tests that are possible with an oscilloscope! It would make life so much easier. I'm sure that they could potentially devise a way to connect an amplifier and set the output level quick and easy so that you just have to push one button and the oscilloscope would run through a set program that tests for many different parameters and gives you a list of the results at the end, it would also be great to be able to save the results so that you can compare between different amplifiers... You would think that this sort of thing would be possible by now! Having the ability to do individual tests is fine, we have been doing this since the oscilloscope was first invented but we know all the tests needed to do a full test of an amplifier and we have oscilloscopes that are capable of doing it automatically but alas, we aren't there yet. Should someone release such a product, shut up and take my money!
How about this: www.keysight.com/en/pdx-x202150-pn-U8903B/performance-audio-analyzer
@@feedback-loop wow! Yeah so it exists! The first one that showed up on eBay had a price of $24,000 and it's used LoL. I'm not selling my kidneys for that... I think that what I was trying to say was that most oscilloscopes have an FFT function and I have seen people who have made their own math to calculate the rms output of the amplifier, I'm sure that all these simple things can be consolidated under one menu. I don't have a modern oscilloscope yet and the one that I'm currently using gives no information apart from the signal on screen! I constantly see other people digging into the menu to measure something else which I believe that it could have been placed better in the menu system. For example an Audio hot key which hides options that you would have no use for, or at least give you the ability to hide options that you would personally never use.. Sure, that machine you provided in the link is amazing! And thank you for showing me that, I will keep it in mind for when I win the lottery LoL.. There's older machines that have the same model number but after seeing the current model, the older models just don't interest me even though they are still very capable...
I am not entirely sure I understand your point. It seems to me that my scope is quite close to your requirement: just connect the generator and channel 1 probe to the input, connect the channel 2 probe to the output, push a few buttons, and you have a frequency response plot. And it is not a high-end scope. I think it is from the lowest 1000-series currently available from Keysight and not the highest model there (under $1000). Why older scopes did not offer this? I don't know. It is always hard to say why nobody thought of something before. Combination of factors, as usually, I suppose. The cost of ROM and RAM for extra applications dropped, CPUs are more powerful, screens have more resolution, our expectations of what scopes must offer have changed and so on.
@@feedback-loop yeah you're probably right, I'm being a hypocrite because I don't have a modern oscilloscope, my 20mhz crt scope is as basic as you can get but I knew this when I got it, I do have one of those small pocket DSO212 oscilloscopes, it's great for what it is but it's screen is to small and it's interface is harder to use although not impossible for daily use. You're scope is nice, I don't know what the pro's and con's are of having a single generator built in but in your hands it seems to work out fine which is mostly important at the end of the day, I guess that I will have to get myself an oscilloscope before I start asking for features... Maybe it's just the person who was using his scope that made it look difficult, Just because a person is into electronics, doesn't mean that they specialize in everything! I personally love amplification and almost anything audio (almost) just not DAT machines because I really don't fully understand their operation, so you will never see me working with micro controllers or computers unless it was mine, Audio is where my passion is hence the reason why I watched your video, although I don't limit myself when watching videos, generally I watch anything electronic related because I get to learn things from other areas of electronics that can be useful for audio... This video.... Was perfect! Apart from me having a little rant about oscilloscopes in general, you sir were flawless.. I remember hope that you do more videos like this because I haven't seen anyone else do this... 10/10.