List of PWM Amplifiers. - Page 4

Originally Posted by millwood

that wouldn't be necessary: you can simply multiple a pwm or pcm or bitstream signals in the digital domain and then feed that signal to the amplifier. For example, multiplying the signal by a factor greater than 1 increases its volume and multiplying the signal by a factor less than 1 decreases its volume.

let me use a simple example. see you are dealing with a 4-bit pcm signal, which takes the form of 0110 (equates to a value of 6) at this particular moment. see you want to double its volume (to 12), you just shift it 1 bit to the left, 1100 (equates to 12). feeding that
signal to a class d amp (either directly or through a dac) will double the output voltage.

or you can shift it to the right by 1 bit to reduce the volume by 50%, 0011 (which equates to 3).

the same principle applies to your typical 16-bit PCM used by your CD, or DTS / DD signal on your DVD.


In other words, you want to do volume control or processing (of which volume control is a form) in the digital domain, and in the pre-amp section, not in the amplifier.

no need to alter rail voltage dynamically for a class d amp - too complicated and without any meaningful gain.

Originally Posted by Yves Smolders

You don't alter the input signals amplitude to control the volume - you control the rail voltage that is fed to the power transistors. Since the transistors are always on or off, the same feeded signal can be made "harder" or "softer" at the output if you change the voltage on the rails feeding the transistors. In conventional designs, this rail voltage is fixed (in class A, AB, and D) - Class H designs alter the voltage of the rails also, but for a different means: They track the incoming signal to increase efficiency.

Originally Posted by millwood

a class D amp doesn't feed its digitzed output (PWM waveforms) directly into a receiver. It does so through a low-pass filter, which converts the pwm waveform into analog voltage (effectively a DAC).

So the combination of a pwm output stage and the low-pass filter forms the digital amp and outputs an analog signal.

Originally Posted by GoldenEarDrums

However, this procedure will require tremendous processing. Imagine recalculating every bit (no pun intended) of information even with the slight change in volume (gain).

Originally Posted by GoldenEarDrums

It uses PSVC (Power Supply Volume Control) which varies the (fixed) voltage of the PS via a controller built in the chip

Originally Posted by GoldenEarDrums

and is completely separated from the signal path therefore providing the cleanest unhindered volume control system....

Originally Posted by millwood

...
multiplying in the digital domain would be the cleanest path.

... those digital volume controls chips are a dollar a dozen (the upc line from National for example) and each controls 2 or 3 channels too.

Multipliers are some of the most basic elements of digital circuitry. and if you want, you can even use a memory chip for that - I actually have a patent on that.

Originally Posted by millwood

Back to the point that timing of a pwm amp being analog. You could conceivably use the pcm signal to control the duration of the pwm on / off state and have the amp being entirely digital.

For example, if you see a signal of 0101 (again, in a 4 bit pcm format), you turn on the output device for 5 cycles (or a multiple of 5 cycles). in this way, all you need is a sqaure wave generator and a down counter that automatically resets itself.

something like this can be even implemented ina fpga device. and can be very fast.

Originally Posted by millwood

those pwm amplifiers are essentially your switching mode power supply. Except that in the case of a power supply, the "input' signal is a reference voltage / current. You can take such a power supply and feed its ref node with an audio signal and it should sign.

As a matter of fact, there are people using sg352x devices and mosfet gate drivers to make high performance pwm amps - IRF's IRAudAmp1 is such an example.

Originally Posted by GoldenEarDrums

I do like your idea of this bit-dynamic VC and would like to know more about your patented product.

must be the 'good' distortion everyone keeps talking about similar to tube amps