Why is EVERY amp on this polish website at low signal output 20 dB worse than @amirm´s measurements

[restorer-john]

100 milliwatts starting with about minus 50 dB or so (0,3%)
But @amirm ´s measurements are starting with about minus 70 dB or so ….

100mW@4R is just 632mV.
5W@4R is 4.47V, 7 times the voltage and a ~17dB voltage difference.

250mW@8R (1.414V) is where THD+N is required to be specified from (to rated power). ASR will get there eventually in their tests. These things take time.

 

[DanielT]

Has this Polish test dude tested and calibrated his test equipment?

In addition, witch has already been pointed out, different test equipment and or different test methods. Otherwise, that the same brand/model of amplifiers being tested would differ so much, I doubt that.

 

[DavidR]

100mW@4R is just 632mV.
5W@4R is 4.47V, 7 times the voltage and a ~17dB voltage difference.

250mW@8R (1.414V) is where THD+N is required to be specified from (to rated power). ASR will get there eventually in their tests. These things take time.

What is the source for that required specification?

 

[MAB]

What is the source for that required specification?

FTC's amplifier rules:
Trade Regulation Rule Relating to Power Output Claims for Amplifiers Utilized in Home Entertainment Products
Federal Trade Commission
16 CFR Part 432
RIN 3084-AB62

https://www.govinfo.gov/content/pkg/FR-2024-06-12/pdf/2024-12744.pdf

 

[Timmy]

Which program did you use to match the two screenshots?

Adobe Illustrator. You simply need a layer based graphics editor that lets you visually interact its layers

 

[totti1965]

Adobe Illustrator. You simply need a layer based graphics editor that lets you visually interact its layers

Thanx!

 

[Scytales]

According to his post, measurements are done with Neutrik A2-D analyzer. Quite dated to today's standards.

Specifications of this Neutrik audio analyzer out of its user manual :

The specifications of the analog signal generator (first red arrow), also not much detailed (no level is specified), are not impressive. Neither are the specifications of the analyzer (second red arrow).

To my mind, the measurement of the Polish tester are most probably limited first and foremost by the signal generator of the Neutrik analyzer, especially at low level.

And there are caveats about the way the signal generator is connected to the device under test (DUT), especially DUT having unbalanced inputs.

 

[MAB]

That’s »Bahnhof« to me, but I try to follow. The polish chart begins to blur now, I fear

To convert from % to dB:
Distortion in dB = 20*log(Distortion%)
For instance:

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

WebPlotDigitizer is useful for comparing messy graphs like these, especially since one is in % and the other in dB:

WebPlotDigitizer

Here is the comparison using WebPlotDigitizer.

The distortion figure they produced isn't plotted vs. log(Frequency) which limits what can be observed in noise and other measurement artifacts.

The audio.com.pl distortion test results look odd to me. If I overlay it with Amir's measurement, and plot it on a log frequency scale:

No way to tell the details going on below 1kHz in but if I were to speculate, they have quite a bit of mains noise severely limiting low frequency performance. I have more questions than answers on the higher order distortion they see but are absent from Amir's measurements. They do align on the 3rd and 5th HD peaks though!

 

[Scytales]

As per Neutrik A2 user manual, there are two ways to connect the balanced output of the signal generator to the unbalanced input of the DUT (page 28/104) and precaution to take when connecting an unbalanced output of a DUT (such as a typical power amplifier output) to the balanced input of the analyzer (page 25/104) to avoid ground loops.

It would help to know the wiring routine used by the Polish tester for each measured devices, as the optimal way of connecting together DUT and analyzer may differ depending on the tested device.

 

[restorer-john]

To my mind, the measurement of the polish tester are most probably limited first and foremost by the signal generator of the Neutrik analyzer, especially at low level.

The analyzer he is using is not remotely adequate for characterizing modern, high performance high fidelity equipment. It's absolutely fine for a service bench.

 

[restorer-john]

and precaution to take when connecting an unbalanced output of a DUT (such as a typical power amplifier output) to the balanced input of the analyzer

99% of RCA output gear (or most amplifiers) will have the outer (shell or "-") at the same potential, and ultimately tied to the chassis ground. So their 2nd image below is fanciful saying "be sure not to have internal connection". Thing is, much gear is also double insulated (not earthed) so the chassis is floating, but 'grounded' and full of 50/60Hz voltage capacitively coupled from transformers, Y caps etc.

 

[restorer-john]

I have more questions than answers on the higher order distortion they see but are absent from Amir's measurements.

The "high order" is likely IMD products from the fundamental, it's harmonics AND the excessive mains spuriae.

 

[Timmy]

The analyzer he is using is not remotely adequate for characterizing modern, high performance high fidelity equipment.

Which could lead to a question like this:

Why in the world would a guy from Poland who is said to be running a yearly HiFi show in Warszawa use an analyzer that is not remotely adequate for characterizing modern, high performance high fidelity equipment?

 

[restorer-john]

Which could lead to a question like this:

Why in the world would a guy from Poland who is said to be running a yearly HiFi show in Warszawa use an analyzer that is not remotely adequate for characterizing modern, high performance high fidelity equipment?

Because it's likely all he can afford. And much of the cottage-industry produced stuff in Poland would be adequately tested with that analyzer. It was a decent analyzer in 1995, but not in the same league as even an AP System One from several years before.

 

[Timmy]

Because it's likely all he can afford. And much of the cottage-industry produced stuff in Poland would be adequately tested with that analyzer. It was a decent analyzer in 1995, but not in the same league as even an AP System One from several years before.

So shouldn’t he, as a man probably devoted to science, state explicitly to all his reviews and measurements that he is some 30 years behind?

 

[restorer-john]

So shouldn’t he, as a man probably devoted to science, state explicitly to all his reviews and measurements that he is some 30 years behind?

I guess instead of asking me, you should ask the guy concerned.

 

[Timmy]

I guess instead of asking me, you should ask the guy concerned.

Well, I prefer to ask just generally.

Since he himself could have reason enough to declare such a question as a brute example of imperialistic chauvinism, I fear. Would you ask him that question?

 

[JSmith]

Neutrik A2-D analyzer

He'd be better off with a new QA403 for $600;

QA403 Audio Analyzer

12-Aug-2024: The QA403 is back in stock. 29-Jul-2024: The QA403 is currently out of stock for the next 1-2 weeks. It is in stock at Elektor in the EU and Saelig in the US. Click on a graphic below to be taken to the respective website. Affordable and Powerful Audio Analysis The QA403 is our...

quantasylum.com

THD -115 dB (loopback, 0 dBV input range, single-ended, L- shorted, -2 dBV input, 128K FFT, Hann window, 20 kHz BW)
THD+N -105 dB (loopback, 0 dBV input range, single-ended, L- shorted, -2 dBV input, 128K FFT, Hann window)

JSmith

 

[restorer-john]

Would you ask him that question?

Is he claiming his tests are state of the art and accurate? I don't really care about anyone else's testing unless they are making claims they can't back up or are completely wrong, deceptive etc.

My test gear is not absolute SOTA. My best analyzer is the QA-403 which easily gets down to -120dB (0.0001%) THD on loopback from its own DAC based generator. Even better with an external generator. The ADC is the same as the Cosmos, but it has a proper 200k scalable front end and autoranging along with ranging on the generator to keep the ADC/DACs in their sweet spots.

You can cobble together a pile of Cosmos boxes, external DACs, isolators, ranging boxes, attenuators, notch filters and get really close or better than the AP on a few narrow tests, but that pile of stuff doesn't come close to an APX-555B across the board. Neither does my QA-403. But it comes a lot closer than it deserves to.

 

[restorer-john]

He'd be better off with a new QA403 for $600;

QA403 Audio Analyzer

12-Aug-2024: The QA403 is back in stock. 29-Jul-2024: The QA403 is currently out of stock for the next 1-2 weeks. It is in stock at Elektor in the EU and Saelig in the US. Click on a graphic below to be taken to the respective website. Affordable and Powerful Audio Analysis The QA403 is our...

quantasylum.com

JSmith

What I just said but you got in first.

Those quoted figures are also conservative. My QA403 is much better, as are most of them. With cross correlation now in the software, it gets even better again.

With a QA-403, you have no SPDIF in/out, but it's easy to test DACs with PC mirroring.