Microbuzzer.com · Posted on 23-07-2010 by microbuzzer

Speaker audio power amplifier is the voltage signal into the audio signal and drive a speaker sound equipment. PA in the PA plays an important role in the absence of power amplifiers, speakers can not burst, it has not been sound reinforcement at all.
Speaker power amplifier is to use the current controlling transistor or FET voltage controlling the power of the power conversion in accordance with the current input signal changes. Because the sound is different amplitude and different frequencies of waves, that AC signal current, transistor’s collector current is always the β times the base current, β is the exchange of transistor amplification, the application of this point that if the small signal into the base, the collector current will flow through the equivalent of β times the base current, then the signal blocking capacitors used to isolate, to get the current (or voltage) is β times the original large-signal, this is a transistor amplification effect. After continuous current and voltage amplification, power amplification is completed.

Power amplifier is usually 3 parts:

Pre-amplifier, driver amplifier, the final stage power amplifier.

1 match from the role of pre-amplifier, the input impedance high (not less than 10kΩ), can be absorbed in the past most of the previous signal, the output impedance low (tens of Ω or less), most of the wind signal can be transmitted. At the same time, it itself is a current amplifier, the input voltage signals into current signals, and appropriate amplification.

2, drive amplifier from the bridge, it sent the current signal preamplifier for further amplification, to enlarge the power of the signal driven into the end of the middle-class power amplifiers work. If no driver amplifier, the final stage power amplifier can not send voice signals.

3, a key role in the final stage power amplifier. It will drive amplifier current signal sent by the formation of high-power signals to drive speakers sound, and its technical indicators for the whole power amplifier specifications.

PA’s main technical indicators:

1, rated power (rate power): refers to the continuous sine wave power sine wave at 1kHz input and a certain load, the harmonic distortion is less than 1% of the power output, expressed as W / CH (W / channel ). In general, the greater the power rating, the higher the cost.

2, total harmonic distortion (THD): refers to the higher percentage of fundamental harmonic accounts, the smaller the better total harmonic distortion, total harmonic current distortion of a good power amplifier can achieve 0.02%

3, conversion rate (slew rate): the voltage increase rate per unit time, unit volts / microsecond, which reflects the power amplifier transient tracking capabilities of voice signals is a transient indicator.

4, damping factor (damping factor): defined as the power amplifier load impedance (high-power tube speaker internal wiring line resistance with resistance), such as 8Ω: 0.04Ω = 200:1, generally require relatively large ratio, but not too, that the Assembly speaker sound is too thin, too small will make the sound muddy, the sound level is poor, poor audio and video distribution.

5, output impedance (output impedance) (, or rated load impedance): usually 8Ω, 4Ω, 2Ω equivalent, this value is smaller, the stronger the power amplifier load capacity. The single, the rated load for the 2Ω power amplifier, can bring four impedance 8Ω speaker sound, and distortion is small.

The characteristics of power amplifier to provide signal power to the load amplifier, often referred to as power amplifiers. PA work, the signal voltage and current range of relatively large, and therefore has many different characteristics of small-signal amplifier.

Efficiency power amplifier

The essence of the power amplification by controlling the transistor to the DC power supply to the amplifier power into AC power load. AC output power and DC power supply power is closely related series. DC power supply providing a power amplifier power how can the number of AC output power into it? We certainly hope that the PA can best DC power (PE = EcIc) one hundred percent into AC output power (Psc = Uscisc) in fact it is not possible. Because the transistors themselves have a certain power consumption, various circuit components (resistors, transformers, etc.) to a certain degree of power consumption, which have efficiency problems. Amplifier output power efficiency η Psc and that the direct power supply PE turnover ratio, that is usually expressed as a percentage:

η = Psc / PE

Usually expressed as a percentage:

η = Psc / PE × 100%

The higher the efficiency that the better the performance of power amplifiers.

Crystal Hugh tube in large signal operating conditions, the working point at the next big swing. Once the operating point out of input or output characteristic curve of the linear region, nonlinear distortion occurs. So the audio power amplifier, the output power and the nonlinear distortion always considered together. Audio power amplifier has two general indicators of the maximum output power and the maximum date no distortion output power. The former shows the maximum load capacity of the amplifier, which indicated that the capacity of non-distortion amplification. For example, two amplifiers are 50-watt maximum output power, but one of the largest non-distortion power is 40 watts, another maximum power is 30 watts without distortion, the performance of the former than the latter would better.

Three modes of operation amplifier speaker

Power amplifier according to the different working conditions, can be divided into A, B and B class of three. A feature of the amplifier in the output characteristic curve of work Click the middle of linear region, the signal current flow in the whole cycle all, distortion but low efficiency, output power is also small. B amplifier in the base current is zero Click to which the output characteristic curve, the signal current flows only in the half-cycle, high efficiency, output power, but a serious distortion. The third amplifier operating point B enlarge the election was not as low as, or as high as A, the current cut-off time is less than half of cycle performance between Group A and Group B between.

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