hifi.slovanet.sk

[PMA]

To, co píšeš, je totální kravina.

[boxer]

i]ještě abyste se rozplívali nad tím, jak je shnilá ryba chutná....[/i]

Mistr jistě chtěl napsat .....rozplivali se (kol sebe)

[miero]

Mozno merali nejaky vadny kus...


Pulse 1 Integrated Amplifier:

[Tico]

2 Bacil: Ted jsi mi fakt rozsiril merici obzory Ovsem bez muceni se priznavam, ze si nepamatuju kazdou kravinu a ze Ackova krivka je az tak milosrdna na 100Hz.
Nic to ale nemeni na tom, ze tajovej hnuj je slyset a to tak, ze dost. Nedavno jsem tady resil odstup asi -90dBV (100Hz a sudy harmonicky) na vystupu z BB-DACu. Po zesileni v konci to dela nejakejch -65dBV a neni to nic prijemnyho. Po oprave zapojeni zdroje je to nekde kolem -108dBV a je to akceptovatelny. Tahle mrsba je ovsem kapku jina liga

[bacil2]

... a mimochodom, ak je toto meranie 0,1w/8ohm (ako tam píšu gréci):
http://avmentor.gr/reviews/lab/group_test_integrated_amps_2010/high_resolution/leema_acoustics_pulse_noise_spectrum.jpg
... tak potom hodnota odstupu s/š pre sieťový brum bude cca -63dB(A) pri záťaži 0,1W !!! ... a brum sa oficiálne meria pri 0W!

[BV]

A vidíš tam niekde čiaru 1kHz?? Je to šumové spektrum na výstupe zosilňovača bez budenia,takže skutočne "pri 0W", merítko je nejasné (dBr - relatívne k čomu??). Pri meraní 10W/8ohm je to jasné, je to na 100Hz relatívne -60dB k 9V (čo je 10W na 8R), takže to bude cca -40dB relatívne k 1V, alebo asi 10mV brumu 100Hz na výstupe bez signálu. Pritom je to len tá jedna zložka, je ich tam celý les a ich výkon sa spočíta..A to je neoddiskutovateľne "humus", či s filtrom alebo bez (pre ilustráciu, včera som oživoval jeden "pokus", na výstupe konca so ziskom 26dB je bez budenia 14uV RMS v pásme 20Hz-22kHz, bez filtra, čo je úroveň šumu a brumu na výstupe -97dBV ..)
Chybný kus to asi nebude, všetky parametre sú biedne, odstup, skreslenie, SR, výstupný odpor.. "Chybné" sú asi údaje výrobcu, keď si dovolia napísať toto

[Tico]

...jeden můj bejvalej kolega v takových situacích používal hlášku: "A teď mluv, když koktáš!"

[bacil2]

BV: ja nemám klasické „grécke vzdelanie“, ale pod tým grafom je napísané toto:
Φάσμα θορύβου. Στάθμη αναφοράς: 1kHz, 0.1Wrms/8Ohm, βραχυκυκλωμένη είσοδος.
...takže minimálne je z toho jasné, že 0dB zodpovedá 0,1W

... a z toho čo píšeš ďalej vidno, že ani ty netušíš načo je dobrý A-filter ...


Tico: dnes si každý, kto má do riti díru môže kúpiť kartu do pc a „merať“ čo chce ... to, že netuší čo vlastne meria, prečo to meria a keď aj niečo nameria, tak nevie ako to má korektne interpretovať, to už dnes nikoho moc nesere ... a pozerám, že ste tu takí viacerí!

[Tico]

2 bacil2: Řekneme, ze ten blbeček s měřící PC kartou bych moh bejt já, ale v případě BV bych si to 2x rozmyslel
Znova opakuju, ze v tom měření 0,1W/8ohm chybi spektrální cara merici frekvence 1kHz a pokud tam něco je, pak je to 20dB pod síťovým brumem. Varianta b) ze to Řekové měřili s vybuzenim jednoho kanálu na 0,1W a měřili spektrum druheho, je asi pravděpodobnější.

[BV]

[PMA]

Na úrovni odborné argumentace a la bacil2 se s nimi vůbec nemá význam bavit, vysvětlíte to 10 000x a po 10 001 přijde stejné pako které netuší, o co jde a startujete nanovo od základních termínů, které nechápou. Je to totéž, jako argumentovat s Cimrmanem.

[bacil2]

[PMA]

A filtr s tím stejně mnoho nenadělá, pro podobný krám asi 9dB, pokud chceš bacile diskutovat konkrétně tak máš možnost nad těmito měřeními odstupu bez filtru a s A filtrem.

[bacil2]

[PMA]

Zlepšení s A filtrem je jen v případě jedné čáry 100 Hz ve spektru. Co mně vadí, jsou plané kecy.

[bacil2]

[Tico]

...jak to s tím krmením trollů?

[BV]

[dStam]

Hello from avmentor.gr,
we understand (well, sort of, by using Google translator... ) that during the last few days there is a discussion here about an amplifier we reviewed some years ago, especially about its noise performance and the interpretation of the relevant graphs and static measurements. We do not intent to be intrusive of course, but we are willing to help by describing the methods and equipment used. If you feel that this is appropriate and/or desirable please let us know, by posting here or sending a PM. Since we can not speak or write in Slovak language the explanation will be in English. We'll do our best to reply as soon as possible.
Dimitris Stamatakos
Akraies Ekdoseis/avmentor

[Lajos1981]

[iljas]

[BV]

Hello Dimitris,
welcome and thank You for input! The only real question is scaling in noise measurement graph, dBr, relative to what dBV or dBu ?). Picture is marked as "1kHz, 0.1Wrms/8Ohm", but here is no visible spectral line at 1kHz, so no known reference level here, only noise and mains components.

[dStam]

Some Notes about the Leema Acoustics Pulse amplifier noise measurements.

Leema Acoustics Pulse amplifier was reviewed during February 2010 as part of amplifier group test. The full test starts here: www.avmentor.gr/reviews/group_test_integrated_amps_2010_0.htm , and the reader can find some tabulated data here:
www.avmentor.gr/reviews/group_test_integrated_amps_2010_14.htm

First of all, we would like to underline the fact that it is rather difficult to compare lab measurements from different sources, i.e. between a publication and a manufacturer, or between publications, or between manufacturers, or even within the same publication but in very different time periods, to be honest, since the lab scripts are in constant development. More often than not, measurement methods, lab equipment and conditions are different. A much more meaningful approach is to compare results from different devices within the same realm. This is why we are doing group tests. It is a good opportunity to compare devices using the same, well defined, evaluation method.

Now, about the lab evaluation of the Pulse (and the rest of the amps in this group test):

Lab equipment:
The main instrument used was a dScope III dual domain audio analyzer (from Prism Sound). This is not just a standard PC card but a complete lab grade system with software running in a host computer and a rather sophisticated signal acquisition front end.
To load the amplifier, both a convection cooled standard resistive load and a complex (i.e. resistive/reactive) load were used during the evaluation. For noise measurements, we used only the resistive load.
Waveform monitoring was performed by a Hameg HMO3524 oscilloscope.
Power supply to the amp was monitored (but not controlled) via a power quality analyzer (a Fluke 43B) to ensure that basic power parameters are within the acceptable limits, during the test.

In total, each amplifier review contains two graphs and a static measurement related to noise.

The “static” measurement is a dBr(A) measurement, meaning that there is an “A” Filter weighting and a voltage reference level (that could be translated to a power reference level, since the load is known).
During this test we selected a rather low reference level on purpose (0.1Wrms/8Ohm), because most manufacturers give figures in full (or high) power levels but in practice, the end user listens to a much lower level. The static measurement is a simple number and a comparison between the devices in the group test is easy. Long after this group test, we amended this reference power level to the more “comfortable” level of 1Wrms/8 Οhm. Results proved to be subjectively “bad” and difficult to interpreted by our readers.

The “Noise Spectrum” as the name implies is the spectrum of the residual signal present at the loaded amplifier output with no signal at the input. In fact, the input is shorted with special plugs. The vertical axis of this graph is in dBr, the reference being a voltage level that was measured and set before the noise acquisition starts (again 0.1Wrms/8 Ohm, or -to be more precise- the voltage corresponding to this power level in an 8 Ohm load). Therefore, the resulting spectrum does not contain a reference tone, only noise components, mostly hum (50/100Ηz related and their intermodulation byproducts) and high frequency noise both from the amplifier and the environment. This is a useful graph, to evaluate the main sources of the noise in an amplifier, which, most probably, is the power supply.

Since it is a general rule that noise measurements are performed with no input signal (most methods use a signal to set a reference level, then cut off the signal and measure the residual) the third graph (Output spectrum analysis at 10Wrms/8ohm) does not qualify as such, directly. Its main purpose is to asses the spectral content of the output with a signal present at the input, mainly displaying HD and ΙΜ components. Nevertheless, there is some “noise related” information here, tied to the performance of the power supply while the amplifier drives a load. If you check the whole group test, you will find some devices with different spectral content between those graphs. A justified expectation here would be no changes at all, or -at least- the just very small ones. Obviously there would be a difference in dBr because the reference is different!. Also, this spectral analysis could be used to pinpoint and resolve any ground loop problems related to the amplifier hookup with the measurement system. As a general practice you select a small FFT size (to speed up the acquisition since you do not need a high resolution result here) and try different cabling and grounding routes, observing the 50Hz component. It is a rare situation but it happens…
Finally, all the measurements in the lab evaluation (except the volume pot tracking, for obvious reasons) are made with the volume control to its maximum (i.e. no signal attenuation).

I hope this helps.

[BV]

OK, so reference level in noise measurement is about 0,9V RMS (corresponding to 0,1W/8ohm). So we can look at this as "nearly" dBV referenced. And highest level spectral line at 100Hz is at level about -55dBV or -65dB ref.1W/8ohm, as is usually measured. IMO, it is very poor result.

[PMA]

Hi Akraies,

we are mostly discussing the very poor signal to noise performance of the amplifier tested. We can see that for a 10W/8ohm spectral analysis measurement, 100Hz spectral line is only -60dB below the base frequency line at 1kHz. This is a very poor result and I cannot recall any other power amplifier with such a poor result. 10W/8 ohm is 8.94Vrms 1kHz signal and -60dB equals to 8.94mVrms at 100Hz. This is very bad. Any usual amplifier would have 100Hz line about -90dB to -120dB referred to 1kHz 10W/8 ohm.
Not only the amplifier has the 100Hz line very high, but also the whole set of mains line frequency multiples.
And harmonic distortion is very poor as well.

Regards,
Pavel

[SamuelJackson]

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