Hi snazzed,
Thanks for contributing but there are some mixed-up statements in your explanation of amplifier classes.
While it's true that the output transistors switch on and off in a Class B analog amplifier, the term "switching amplifier" is only applied to Class D digital amplifiers that use high-frequency switching to modulate the output stage.
A Class A/B analog amplifier isn't a switching amplifier because a small current is constantly left on through the output transistors to prevent distortion when the output devices alternately amplify the opposite sides of the waveform.
Here is a guide I wrote some time ago for the AudioFile newsletter that defines the various amplifier classes:
Class A designs have current constantly flowing through the output transistors even if there is no incoming audio signal, so the output transistors are always on. This type of amplifier has the lowest distortion of any but it’s extremely wasteful and inefficient, dissipating 80% of its power in heat with an efficiency of only 20%.
Class B amplifiers use output transistors that switch on and off, with one device amplifying the positive portion of the waveform, the other device the negative part. If there is no incoming audio signal, then no current flows through the output transistors. Consequently, Class B amplifiers are much more efficient (about 50% to 70%) than Class A designs, however there may be non-linear distortions that occur when one set of transistors switch off and the other set switches on.
Class A/B amplifiers combine the virtues of Class A and Class B designs by having one output device stay on a bit longer, while the other device takes over amplifying the other half of the audio waveform. In other words, there is a small current on at all times in the crossover portion of each output device, which eliminates the potential switching distortion of a pure Class B design. Efficiency of a Class A/B amp is still about 50%.
Class D amplifiers, although there are a number of different design variations, are essentially switching amplifiers or Pulse Width Modulator (PWM) designs. The incoming analog audio signal is used to modulate a very high frequency PWM carrier that works the output stage either fully on or off. This ultra-high frequency carrier must be removed from the audio output with a reconstruction filter so that no ultra-high frequency switching components remain to corrupt the audio signals. As previously mentioned, Class D designs are extremely efficient, typically in the range of 85% to 90% or more.
The BASH amplifiers, originally a Toronto-based company now owned by Sonavox, are a design unto themselves, but are basically a different type of Class D switching amplifier. Axiom used BASH subwoofer amps in the late 90s and into the 2000's.
The current EP175 subwoofer now uses our own Axiom-built amplifier which is a Class D switching amplifier with an analog power supply that is unique (most Class D sub amplifiers use high-frequency switching power supplies).
BASH amplifiers continue to be used by many other subwoofer companies.
Regards,
