Tripath company "invented" and manufacturered class-T amplifier ICs which is a slightly modified class-D circuit. It didn't work very well so they went bankrupt 4 years ago. Many Chinese companies still sell the ICs or copies of them.
You can just detach the speaker from ur audio device, then build an amplifier with POT at the output. Now varying the POT, the output voltage changes and thus the output volume. So the intensity of sound = Voltage at the output.
A modern audio amplifier has an extremely low output impedance (0.003 ohms to 0.04 ohms) that damps the resonances of a speaker. If you connect a huge expensive pot at the output to control the volume then the pot will burn up and the speaker will resonate and sound boomy like a bongo drum. Therefore a small inexpensive volume control is used at the input of the amplifier where the power is very small.
Many Chinese websites are trying to sell amplifiers made with obsolete Tripath class-T amplifier ICs or copies of them.
I stay away because Tripath went bankrupt.
A company called 41Hz Audio (in Sweden) used to sell and still might sell amplifiers that use Tripath or copies of their ICs.