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Amir Buys a New Audio Precision Analyzer (APx555)!!!

March Audio

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How about



How about Boris Johnson - the Keith Moon of the Tory party?

FWIW we don't really wan't GB back after being deserted by it for the EU. o_O

Boris is brilliant. :) A clever guy pretending to be a buffoon........converse of the US situation where Trump is a buffoon pretending to be a clever guy.......

I do laugh, Australia a republic? There is far more TV coverage of the Royal family over here than there is in the UK. Oz cant get enough of it :)
 

Wombat

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No more dangerous than audiophile beliefs that are pandered to. :facepalm:
 

Wombat

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Boris is brilliant. :) A clever guy pretending to be a buffoon........converse of the US situation where Trump, is a buffoon pretending to be a clever guy.......
Pretending to be a buffoon is not clever unless you need to be supported by buffoons. However, they will out you as a user. Maybe slowly, but surely.
 

Wombat

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Oh everyone knows what Boris is about, I just find it enjoyable to have a politician with a bit of character.


You will like POTUS, then.




Back to regular programming.:facepalm:
 
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DonH56

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I had Matlab for years until they changed their pricing structure. I paid about $200 to $300 USD a year for maybe a decade, then they decided a major upgrade was worth ~$1300. I dropped it (or rather just stuck with the old). A few years later I needed it for a college class I was giving and called Mathworks; they actually gave me a full-blown license. Guess it pays to be a teacher. Since then they have rolled out "individual" pricing so I re-upped but haven't had time to use it much. Similar thing happened with Mathcad but they have never rolled out cheaper pricing (I think, quit looking a few years ago) so I am running an ancient version. I hope it doesn't break as I have a ton of audio-related Mathcad files; that was my main tool for years, and my company does not provide Mathcad (they do Matlab but restrict "private" use).
 

DonH56

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For many applications the Octave (open source and free Matlab alternative) is good enough:
- https://www.gnu.org/software/octave/

At least if your code does not depend on "premium" Matlab libraries.
Yes, that is an excellent suggestion! I have piddled with Octave at work some (we use Python extensively so also NumPy and SciPy) but the problem is I do use a lot of Matlab-specific toolboxes, mainly for RF and control stuff, but a couple of years ago started playing with their audio packages. That said, Octave is very good, the plotting library in Python works very well, there is lots of third-party support, and if I did not have the investment in Matlab already would agree with starting there. Plus I am not a real programmer, though end up doing quite a bit of it these days, more an analog dinosaur.
 
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... Typical audio analyzer is an analog to digital converter (ADC) with a bunch of software.
In the case of Audio Precision analyzers, they also have excellent auto-scaling "gain" stages that can amplify or reduce the levels of signals to allow very wide dynamic range. When fed strong signals though, the ADC can produce its own noise and harmonic distortion which can be confused with the device under test.

The late Dr. Tom Kite explains and demos this well in this short video:


Technically, this is the simplified architecture of APx555:

View attachment 13093


In addition to above analysis hardware, the generator is also improved to have lower distortion. Ironically, this is an analog solution that beats the digital one (a DAC)!!! Sometimes old technology beats new. :) Combined these too and looping the APx555 to itself produces this on my bench: ...
Hi and sorry to jump in but i am confused. I am not an expert. But you talk about a fully analog device here ? but from the schematic i see that the incoming analog signals are still converted to digital. So the device is actually like a state of the art AD/DA converter ? I would be curious to know which ADC and DAC are used in this exceptional equipment. And sorry but i have to ask a silly question ... does this device sound ? can it be used as a high end musical ADC o DAC ? the noise is practically absent and the distortion as well.
Thanks a lot for all your excellent work.
Kindest regards, gino
 
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amirm

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Thread Starter #112
Hi and sorry to jump in but i am confused. I am not an expert. But you talk about a fully analog device here ? but from the schematic i see that the incoming analog signals are still converted to digital. So the device is actually like a state of the art AD/DA converter ? I would be curious to know which ADC and DAC are used in this exceptional equipment. And sorry but i have to ask a silly question ... does this device sound ? can it be used as a high end musical ADC o DAC ? the noise is practically absent and the distortion as well.
Thanks a lot for all your excellent work.
Kindest regards, gino
No, it can't be used as a music device. And the answer you seek is in the post you quoted.
 
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Hi thanks a lot for the kind and valuable reply. I understand i have to study more in depth the description of the unit. Kind regards, gino
 
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How does the residual input noise relate to the thermal noise w.r.t. the input impedance? I am a bit confused because the noise figure this device is showing is below the noise level that one can calculate for a 100k resistor (around -115 dBV).
 

SIY

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Depends on the source impedance- if the input is shorted or the source impedance is otherwise low, the input impedance's Johnson noise won't be seen.
 
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Seen from the analyzer input, the source impedance is in parallel with the nominal input resistor. Both are from the input to ground. So what you see, noise-wise, is Zsource // 100k. For a source with a few 100 ohms Zout, that's what determines the noise resistance.
 

pma

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Taking into account what excellent instrumentation you have, Amir, I am wondering why only 1kHz spectrum, SINAD and level dependent distortion is examined in deep. I have written my reservations in this post:
https://www.audiosciencereview.com/...a-1-vintage-amplifier-review.9576/post-255278
however it seems to be overlooked or not worth answering. So please let me repeat my question in this thread, where it probably belongs:

Amir, I am missing THD (+N) vs. frequency plots in your set of measurements, or CCIF 19+20kHz twin tone measurement. These old amplifiers from seventies were often good in THD 1kHz, however not so good in THD 10kHz or high frequency CCIF IMD. THD 1kHz or SINAD 1kHz does not tell a big story. They also often had TIM/DIM issues. Would not you consider to broaden your measurements, for the readers to get more complete view of the amplifier tested?
 

restorer-john

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@pma

Yamaha conservatively specified THD from a few milliwatts to rated power across the entire bandwidth from 20Hz -20Khz.

They also specified the IMD at half rated power, 60Hz:7kHz 4:1 at less than 0.003%.


1572332345477.png


They also often had TIM/DIM issues.
"They". Let's be specific shall we? What actual (brand and model) amplifiers had TIM/DIM issues? What were those issues exactly? Pick a few you can think of- I may have them in my collection to test.
 

pma

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@pma

Yamaha conservatively specified THD from a few milliwatts to rated power across the entire bandwidth from 20Hz -20Khz.

They also specified the IMD at half rated power, 60Hz:7kHz 4:1 at less than 0.003%.

"They". Let's be specific shall we? What actual (brand and model) amplifiers had TIM/DIM issues? What were those issues exactly? Pick a few you can think of- I may have them in my collection to test.
There are not many trusted measurements on vintage amplifiers left. It is rather in a memory, that anything that had uA741 and similar parts inside used at higher than 1V level had SID/TIM issues. On the other hand, poor linearity at higher frequencies, compared to 1kHz specs, can be seen in many amplifiers until now. Just one example


https://www.stereophile.com/images/archivesart/207clas.5.jpg

207clas.5.jpg


That's why I am asking Amir to measure not only at 1kHz and to ad 19+20kHz IMD. 60Hz+7kHz is nothing, it is an easy task for the amp.
 
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