Optoma NuForce Support Center

Does NuForce's amplifier experience crowding-out phenomenon as in conventional audio amplifiers?

 

Many audiophiles have observed that the main voices in a recording when produced by amplifiers that have impressive specification numbers are crowded out or submerged in the presence of strong basses. Yet these amplifiers boast about 100kHz bandwidth. Is this a human hearing characteristic or the amplifiers have something strange going on? While it is true that human ears are highly non-linear vs. amplitude and frequencies, it is also true that no datasheet of transistors contain straight lines on any parameter such as gain (or rise time) vs. any other parameter such as drain/collector current (or the voltage across the transistor terminals). In particular, the current gain of a bipolar transistor or the transconductance of a MOSFET varies not only with the collector current or drain current but also the frequency of the input signal. For example it is well known that the transconductance of a bipolar transistor is at first approximation proportional to the collector current but on the other hand its current gain decreases with collector current. Therefore when a bass note appears during a continuous main voice, the gains of the transistors become actually lower than during the absence of the bass note, especially a strong one, because the transistor currents are higher during the vibration of the bass note, the refore its F.sub.t also go lower, causing the higher frequencies of the main voice to be actually less amplified. Thus in conventional amplifiers, especially class-AB amplifiers using bipolar transistors, the crowding-out or submersion of high-frequency voices is real. NuForce's amplifiers on the other hand do not suffer from this crowding-out phenomenon. This is because the output MOSFETs only switch between ON and OFF regardless of the amplitude of the audio input signal, the gain in such amplifiers is independent of the transistor current level. NuForce's amplifiers have exceptionally huge bandwidth exceeding 100kHz and very low phase shift in the same frequency range. Therefore all the audio frequencies and their pitch-defining harmonics are faithfully reproduced. Additionally its extremely high damping factor (exceeding 4000) guarantees very tight bass reproduction.

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