Classes of equivalent power A, AB, B and Max
For direct comparison of amplifiers, the power characteristics are determined for several modes by analogy with the classes of operation of the amplifiers: A, AB, B, and Max.
Usually, at the minimum volume level, the amplifier works with minimal distortion, in pure mode, equivalent to class A. The numerical value of the distortions in class A can be large, but we do not hear them scribbically. When adding a volume level, distortions grow and change their character.
We identify the thresholds for the transition of a change in the format of the spectrum and determine the power levels for different distortion formats.
If we compare two amplifiers with an equal amplitude, where they have different types of spectra for this amplitude, then the amplifier with a higher probability of better quality will sound, whose equivalent class will be closer to class A.
Clean Mode - Class A
This is a mode without harmonics of high orders. This is like the most qualitative "clean mode". To determine the equivalent mode of class A, a mask is used, which strictly limits the amplitudes of the harmonics.
The pure mode is now such a mode, according to the spectrum of which we can say that the amplifier works as in class A. This is the absence of high-order harmonics and a significant decrease in the amplitudes of the harmonics toward higher orders. В старых отчетах это был "чистый/clear" режим.
An exception to this rule can be devices with their own DAC and analog volume control, where higher-order harmonics are produced not by an amplifier, but by a DAC.
Some amplifiers may not have a clean mode. In this case, the minimum values are fixed. Our goal is to compare the amplifiers, and for the general standardization of the reports, the amplifier must have all modes defined.
With standardization, it will be possible to open a section with direct parameter comparisons:
AB class mode
This mode is the development of an optimal mode close to the pure mode. In this mode, the values of the harmonics are small and decrease in amplitude toward higher orders. Spectra at the same time look like in AB mode.
This mode is also the development of the optimal mode, but already close to the clipping mode. This is a higher level of harmonics, but similarly decreasing in amplitude in the direction of higher order.
This is the mode before the point of the amplifier's transition into clipping. In this mode, the harmonics do not decrease or reach a high level.
Not only conventional amplifiers, but also players, smartphones, laptops, combines and other devices are being tested. When setting the maximum volume level, the amplifier circuit could give a higher signal level, but this level is limited to the output level from the standard DAC (or codec). At the maximum amplitude, the thresholds for current and voltage for all modes can be the same. On the thresholds of voltage and current, it is determined, in groups of which equivalent classes the amplifying part falls. This is roughly the same as dividing cars by clearance, up to 10 cm, up to 15 cm, up to 20 cm instead of ranges from 0 to 10, from 10 to 15 and from 15 to 20 cm.
An important part of determining the thresholds for current and voltage is the possibility of more accurate comparison of the amplifiers by loudness by converting the voltage to "musical" power, taking into account the correction for the current according to the density of the musical signal.