2006 metų straipsnis, D klasės progreso prasme, jau akmens amžius, sukurti nauji elementai, čipai, moduliai, technologijos. Su dabartiniais komponentais, jei viskas daroma korektiškai, tai straipsnyje paminėtų bėdų beveik nebus. Dabartiniai net nebrangūs D klasės moduliai jau labai perspektyvūs. Blogesnis damping faktorius paprastam D klasės stiprintuve gali būti visai neaktuali problema, nes nevisada reikia didelio dampingo. D klasės schemoje, įvedus neigiamą grįžtamą ryšį (NGR), dampingas didėja. Su NGR mažinama išėjimo filtro darbo priklausomybė nuo apkrovos varžos, gerinamas filtro tiesiškumas ir impulsų sinchronizavimas. Gerai padaryti ir neperlenkti su NGR nėra paprasta, todėl jis ne visada bus pilnai naudojamas pigesniuose variantuose. Visos neigiamos nuomonės apie D klasę sudarytos remiantis senų teorijų prielaidom, kad gali būti tos ar kitos problemos, kurios dabar jau išspręstos arba buitiniuose variantuose net neaktualios. Iki šiol buitiniai D klasės stiprintuvai daugiausiai buvo paplitę ten, kur reikia, kad būtų efektyvu ir nebrangu, todėl dažnai su visom dėl pigumo nesutvarkytom problemom. Dėl sudėtingų konstrukcinių ir techninių niuansų, D klasė buvo labai nedraugiška DIY mėgėjams, kas automatiškai "programavo" neigiamą iki to nepriaugusių mėgėjų nuomonę. Bet jau yra aukštos klasės pilnai padarytų modulių, manau, greitu laiku situacija pasikeis. Artimiausiais metais (nes jau pribrendo), pasipils vidutinės-aukštesnės klasės naminiai stiprintuvai, bus "mėsos" gausiems palyginimams ir daug kas "praregės". :)) On 2013.05.02 09:49, Signalizacija wrote: > The whole reason for existence of Class D is efficiency. > > ... > > If Class D were perfect, it would have swept the world and there would > be no other class in common usage. I'll tell you about the three major > problems of Class-D amplifiers in a moment, but first, here's a > question: how do you make an efficient radio transmitter? Answer: start > with a Class-D audio amplifier. Yes, the high frequencies involved in > Class-D amplification readily propagate as radio waves, potentially > causing interference with radio receivers and other equipment. You might > think that the solution would be to enclose the amplifier in a > substantial steel housing. But that's not where the problem manifests > itself — it's in the cables. The filter that is supposed to remove the > high-frequency components and leave only the audio signal is quite > shallow in slope — 6dB or 12dB per octave — so there's quite a lot of RF > energy still getting out. Clearly, manufacturers take care to improve > the situation and remain within allowable limits, but it is a problem > inherent to Class D. > Class D without the filter. Lab Gruppen's 'Class TD' technology extends > Class D with a claimed sonic performance equivalent to Class AB, but > with Class D's superior performance in terms of efficiency and low weight. > > The second problem of Class-D is that the last thing the signal sees > before it reaches the loudspeaker is the filter. A passive filter made > from capacitors and inductors expects to see a certain load on its > output. Even just looking at the resistance of a loudspeaker and > ignoring its capacitance and inductance, loudspeakers come in 2(omega), > 4(omega) and 8(omega) nominal impedances, and the filter will work > differently according to the impedance of the loudspeaker. Taking > capacitance and inductance into account, the impedance will vary > according to frequency. So the filter design is suddenly very much more > complex: an amplifier that performs differently for different speakers > is going to be a problem. > Thirdly — not finally, but enough for now — a Class-D amplifier has a > relatively poor damping factor. The damping factor is the ratio of the > impedance of the loudspeaker to the output impedance of the amplifier > (it's a little more complex than that, but let's not get bogged down > with details). In simple terms, it's a measure of how well the amplifier > can control the movement of the diaphragm of the loudspeaker. A good > amplifier doesn't just give it a push and hope for the best; it senses > where the diaphragm is from moment to moment and controls its position. > To do that, a high damping factor is desirable, and, as mentioned above, > a simple Class-D amplifier has a low damping factor. > > Clearly, advanced technology can be applied to ameliorate these > problems, but because of them Class-D amplification is used mainly in > applications where efficiency, weight and small size are important. > These include live sound, in-car audio and compact portable systems. > > Clearly, there is more to know. For instance, it's important to know > that the switching frequency must be very high to achieve the necessary > resolution. A switching frequency of around 300kHz, which is around 15 > times the highest audio frequency of general interest, is typical. The > dynamic range and signal-to-noise ratio of the Class-D amplifier are > controlled by the switching frequency — the higher the better. Clearly, > the greater the rate of pulse generation, the more closely the pulse > width will be in proportion to the instantaneous signal level. However, > the drawback of increasing the switching frequency is that the amplifier > will be less efficient. Optimum efficiency would be achieved if the > transistors could switch instantaneously, so that they were in either > their fully on or fully off states, where almost no power is consumed. > But in the real world it takes a little time for the voltage to swing, > and during that time some power is dissipated. So the more often the > swings take place, the more opportunity for waste. Even so, the > efficiency of a practical Class-D amplifier can be better than 90 > percent, which is significantly better than a Class-AB design (78.5 > percent at best and typically closer to 50 percent). > > http://www.soundonsound.com/sos/jun06/articles/loudandlight.htm > > On 05/02/2013 08:25 AM, Dainiushas wrote: >> tu čia stebuklines pasakas kažkokias seki. šiaip jau >> >> On 2013.05.02 07:56, Signalizacija wrote: >>> Dar karta kartoju. Klausai , kalusyk, bet nerikia kist D klases kai >>> kazkokio stebuko. Pats aiskiai parasei, geris gabarituose ir energijos >>> panaudojime. Deja tuo tas geris ir baigiasi. >>> >>> >>> On 05/01/2013 09:17 AM, spakainas wrote: >>>> Ale tu žiūriu vis nepasimokai, negana o.autos'uose grybą pjauni, tai >>>> dar >>>> ir kitur ateini pasišiukšlint. >>>> >>>> 2013.04.30 22:52, Signalizacija rašė: >>>>> Nu maladiec, kad pacitavai kazkoki reklamini straipsniuka >>>>> Klausykis savo lengvo ir ekonomisko stepro, ziurek lcd plastmasini >>>>> vaizda, apsikabines gumine bobike :) >>