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What are the most common measurements for amplifier testing?

Amplifier testing is unique among audio measurements because of the high power levels involved, as well as the amplifier’s direct effect on audio signal quality across various loads and conditions. Measuring amplifiers requires precision and careful calibration, as tests need to address how amplifiers manage power, distortions, and noise under realistic conditions. Amplifier tests are usually conducted at an output power of 1 watt as a standard reference level and can be done using an Audio Precision analyzer along with the APx500 measurement software. 

Power output is one of the fundamental measurements, as it yields insight into the amplifier’s maximum power and efficiency. Tests include Stepped Level Sweeps to generate a THD+N (Total Harmonic Distortion plus Noise) curve, revealing distortion patterns as the amplifier reaches its clipping point. Maximum Output Level measurements further determine peak output by gradually increasing the input signal until reaching a set distortion threshold. For class-D amplifiers and heat-sensitive devices, the CEA-2006 burst method is used to prevent overheating. 

Frequency response tests measure the amplifier’s ability to maintain consistent output across frequencies, typically within a ±3 dB range. Class-D amplifiers often require additional tests with various load impedances due to their sensitivity to impedance changes, which can alter their response curves. 

Noise measurements, including Signal-to-Noise Ratio (SNR), assess the amplifier’s baseline noise, often using a sharp 20 kHz filter to capture accurate results. To address harmonic distortions, THD+N sweeps reveal the amplifier’s distortion behavior over varying levels and frequencies, while intermodulation distortion tests help identify additional distortion not visible with single-tone tests. 

Other measurements like gain, phase, damping factor, crosstalk, and Common Mode Rejection Ratio (CMRR) give insights into the amplifier’s stability, output accuracy, and resistance to noise or interference, especially when using balanced inputs. Each measurement provides valuable data on amplifier performance, supporting the design, evaluation, and refinement of high-quality audio amplifiers.