1. Amplifier Output Power and Bridged Power
This refers to the maximum continuous output power that the amplifier can deliver without distortion, while the maximum power refers to the peak instantaneous power that the amplifier can withstand without damage—essentially the maximum load capacity.
Output Power = Input Power − Power Loss.
When using the bridge function, one audio channel uses two amplifier channels, with each channel responsible for amplifying half of the waveform cycle, combining to amplify the full cycle. However, bridging also has drawbacks: since it is difficult to guarantee complete symmetry between the two channels, distortion may occur. In addition, crossover distortion can be introduced at the transition point between the two half cycles.
2. Amplifier Frequency Response
Frequency response (FR) describes how an amplifier or device processes signals at different frequencies. Like distortion, it is an important technical specification. Frequency response is expressed as a gain-versus-frequency curve. Ideally, the curve should be flat, ensuring that no distortion is introduced after the signal passes through.
3. Amplifier Distortion
Amplifier distortion is measured by comparing the input signal (before amplification) with the output signal (after amplification). The difference between the two is expressed as a percentage.
For speakers, distortion is defined similarly, but the input is an electrical signal while the output is an acoustic signal. Speaker distortion refers to the error in the electrical-to-acoustic conversion process. A distortion within 10% is acceptable, and the human ear is generally insensitive to distortion below 5%. Therefore, it is recommended not to purchase speakers with distortion levels above 5%.
4. Amplifier Sensitivity
For amplifiers, sensitivity refers to the input signal voltage required to achieve the rated output power or voltage, also known as input sensitivity.
For speakers, sensitivity refers to the sound pressure level (SPL, in decibels) measured at 1 meter in front of the speaker when 1 watt of input power is applied.
5. Amplifier Impedance
Input impedance refers to the equivalent resistance at the amplifier’s input terminals. If a voltage source U is applied and the input current I is measured, then the input impedance Rin = U/I.
Analysis:
- For voltage-driven circuits: higher input impedance means lighter loading on the voltage source, easier to drive, and less impact on the signal source.
- For current-driven circuits: lower input impedance means lighter loading on the current source.
In low-frequency circuits, voltage-driven systems benefit from higher input impedance, while current-driven systems benefit from lower input impedance. However, in high-frequency circuits or when maximum power transfer is required, impedance matching must also be considered.
6. Amplifier Signal-to-Noise Ratio (SNR)
SNR reflects the ratio of the amplifier’s output signal power to its noise power, usually expressed in decibels (dB). The higher the SNR, the less noise is mixed into the signal, and the better the audio quality. An SNR below 70 dB is generally unacceptable, while high-fidelity speakers typically require an SNR of 110 dB or higher.
7. Amplifier Damping Factor
The damping factor is defined as the ratio of the amplifier’s rated load impedance (speaker) to the amplifier’s internal output impedance. A higher damping factor indicates better control over the movement of the speaker diaphragm.
8. Amplifier Separation (Resolution)
Separation refers to the degree to which two adjacent frequency peaks (in a frequency response or spectrum) can be distinguished. It depends on both the distance between the peaks and their width. Better separation means clearer distinction between signals, improving resolution.
9. Channel Separation
Channel separation measures how well one channel is isolated from others. Poor separation results in sound leakage (crosstalk) between channels—for example, in Dolby surround sound, audio from the front main channel may “bleed” into the surround channels. Good channel separation ensures accurate sound localization.
10. Slew Rate (SR)
Slew rate (SR), expressed in V/μs, is an important specification of operational amplifiers. It indicates the maximum rate of change of the output voltage in response to a large, fast-changing input signal.
- A higher SR means the amplifier can reproduce signal details more accurately, especially for large or high-frequency signals.
- Typical general-purpose op-amps: SR ≤ 10 V/μs.
- High-speed op-amps: SR > 10 V/μs (can reach up to 6000 V/μs).
This parameter is critical in selecting op-amps for large-signal or high-frequency applications