Output power, output power) : indicates that the power amplifier under certain load, the size of the output power in general on the amplifier specifications in 8 ohm load, 4 ohm load or the output power of 2 ohm load condition, and it will also show that power amplifier in the condition of bridge, 8 ohm load or 4 ohm load when the output power. This output power represents the output power of the power output, not the maximum or peak output. 

Load impedance (the load impedance) : indicates that load capacity of the power amplifier, the smaller the load impedance, suggests that the current power amplifier can ability is stronger, in general, most of the power amplifier minimum is 4 ohm load impedance, the power amplifier minimum load with good quality is generally 2 ohm. Dual channel to 4 ohm load amplifiers, the lowest in the condition of the bridge can load is 8 ohms, dual channel can load 2 ohm power amplifier, can load 4 ohm bridge condition. The bridge can only load up to 8 ohm's power, not the lower impedance, otherwise it will cause the power to burn because the current is too high. 

Stereo (two way) model (stereo mode or dual mode) : general power amplifier inside has two independent amplifier circuit, can accept two different signals of amplification and output, respectively, the working state is called stereo mode (two way). 

Bridge mode (bridge mode) : the bridge pattern is to use the power amplifier within the two mutual push-pull amplifier circuit, so as to produce a greater output voltage, power amplifier after setting for bridge mode, become a mono amplifier, only can accept all the input signal amplification, output for the two way between power output is end. 

Parallel input mode (parallel mode) : this way will be parallel of the two input signals of the power amplifier passage, only input signal all the way to drive two amplification circuit at the same time, the two output end of the output signal is the same. 

Frequency response range (frequency range) : indicates that the work of the power amplifier can be amplified frequencies, generally for 20 hz - 20000 hz, generally in a suffix behind the data, such as 1 / + 1 db, this means that the error of the frequency range or floating range, this value about small, show that the frequency range of frequency response curve is more flat. If the range of the amplifiers is measured at -3 decibels, the sound may not be as flat as that. 

Total harmonic distortion (THD) : indicates that the power amplifier work, because the oscillation or other resonant circuit inevitably produce twice, three times harmonics and the actual input signal, the output end of the output signal is not simply to the input signal is exactly the same composition, but includes the harmonic components of signals, these extra harmonic components and the actual input signal contrast, expressed as a percentage with is called a total harmonic distortion. Generally speaking, the total harmonic distortion minimum near 1000 hz, so most of the power amplifier show that the total harmonic distortion is made with 1000 hz signal test, but some of the more strict factory also provide 20 hz - 20000 hz data within the scope of the total harmonic distortion. The total harmonic distortion is below 1 percent, the average ear cannot be able to distinguish, more than 10 percent can obviously hear the component of distortion. The smaller the value of the total harmonic distortion, the more pure the sound. The total harmonic distortion of the general product is less than 1, 1kHz, but the smaller the number, the higher the quality of the product. 

Intermodulation distortion (IMD) : the distortion of the intermodulation is caused by the transistor work characteristics within the amplifier, resulting in distortion of the waveform of the sine wave. Intermodulation distortion, directly affect the quality of sound, vacuum tube amplifier without intermodulation distortion, so in general the transistor amplifier sounds feeling is not so soft tube amplifiers, comfortable. If the value of the general intermodulation distortion is greater than 0.1%, the sound of the amplification will be hard, dry, and unvoiced. 

Common mode rejection ratio (CMRR), common mode rejection is used to measure the common mode signal by inhibiting power amplifier, a comprehensive index, detailed definition is not here, this parameter is usually expressed in negative territory, for instance - 60 db, this index is also seriously affected the quality of amplifier index, the index number is lower, the better the quality of the power amplifier. 

Damping coefficient, damping factor) : this is a power amplifier resistance and the ratio of load impedance, the impedance of the damping coefficient = speakers & divide; (internal resistance of the power amplifier + sound box line impedance), high damping coefficient of the power amplifier to strengthen control of the speaker unit ability, can make the response of the unit closer to the requirement of the power amplifier output signal, but high damping coefficient of the speakers will result in low frequency ductility, voice and dry. A low damping coefficient can achieve a downy bass, but a low damping coefficient will cause the bass to be tardy and not clean. The general damping coefficient is between 200 and 1000 @ 8 ohms. The quality of the audio box is not good, the resistance of the wire can also affect the damping coefficient of the amplifier, causing the control of the speaker to weaken and the sound disperses. 

Input sensitivity (input sensitivity) : this is a concept of voltage show that when the power amplifier to achieve full power output, in the size of the signal at the input voltage, general power amplifier input sensitivity (0 db) voltage of 0.775 v to 0.775 v (+ 6 db) between, the higher the voltage sensitivity, the lower the input sensitivity. Some high quality amplifiers, low input sensitivity is due to a deeper negative feedback circuit, so it has lower distortion, wider frequency and sound quality. 

Signal to Noise ratio (S/N or SNR or Hum and Noise) : refers to the power amplifier signal voltage and the ratio of background Noise voltage, this value, the greater the show that lower the Noise of the amplifiers. The average professional product has a signal-to-noise ratio of around 100 decibels, and the higher the better (some of them are negative, the smaller the better). The input level gain of attenuation of the amplifier will reduce the signal-to-noise ratio of the amplifier. 

Channel crosstalk (crosstalk) : means that the power amplifier inside through the circuit coupling between two put channel crosstalk, this index is not good, one channel signal will string to another track, thereby not clean voice in another channel, channel crosstalk numerical general about 60 decibels. The lower the number, the lower the value, the cleaner the sound, the higher the separation between the two channels. 

Conversion Rate (Slew Rate) : the response speed of the amplifier is usually measured by the voltage conversion Rate is defined as the voltage rise in 1 millisecond time, if Israel wave measurement is the time needed for voltage from trough to crest, unit is the V/u s, the greater the numerical said transient response, the better, feel the speed of sound, energy concentration. The conversion rate of professional amplifier can generally be 40V/u s. The sound of the conversion rate below 20V/u s will feel sluggish and divergent. 

High-pass filter, high pass filter or HPF) : the sound system, sometimes there will be some extremely low frequency sound (infrasonic) signal mixed in the audio signal, the human ear can't hear the sound signal, but the signal into sound box, will lead to produce self-excited sackbut, and cause the horn is damaged, all, some of the power amplifier with sound elimination filter, some of them are in the panel set the switch, when necessary, to remove unnecessary under 30 or 40 hz Hertz frequency, to ensure the safety of the horn. 

Limiter (limiter) : this is one of the protection of the power amplifier, the amplifier input voltage more than the input voltage sensitivity, to limit of input signal, so as to avoid because of the high input voltage power amplifier clipping distortion. Some of the power limiters are automatically started, some of which are installed in the back panel to control the start of the limiter. 

Grounding switch (ground left) : amplifiers are connected to the power transformer shielding case in general, power amplifier chassis also has ground, but the "ground" and signal "different". When the grounding end of the power supply when there is interference, opening grounding switch to power amplifier chassis grounding to connect can reduce the backdrop, if the power supply ground wire don't connect without interference.