Have a question about multimedia or audio? Ask our Expert, Ken Boyce

Ken:  Where can I get a circuit schematic of a digital, audio amplifier? Thanks

Hi Nate,

The term digital amplifier is one of those terms that can mean many things.  I prefer the following:

All Digital Amp:

This term means that the audio input to the amp is in digital form, usually via a recognized digital audio format like I2S, and that the output is operating in Class D mode where the output signal switches between the voltage rails (+ and - supply, or + supply and GND).  But basically it means that the amplifier should be able to take in digitized samples of the audio at some particular sampling rate, and thru internal means  modulate (usually pulse width modulation) the output switching waveform in some fashion such that IF you applied a low pass filter between the outputs and the speakers, the combination of low pass filter and speaker inductance/capacitance would convert the switching waveform to analog audio you can hear.

Class D amp:

This primarily means an audio amp where the output stage is operating in Class D (switching mode).  Some people refer to this as a digital amp.  But it is really a digital (switching) output stage.   The input can be analog audio, with the amplifier operating a particular A-D modulation scheme which results in the switching output or the input could also be digital as already described, depending upon the particular amplifier design.   Output filtering is general required except in relatively low power cases (generally under 5W, but new designs are pushing the envelope to ~15W) and where the amplifier is physically very close to the speaker (few inches)

Of course there are amplifiers out there that take in digitized audio and do an internal D-A operation and operate the output stage in one of several continuous time analog Classes (A, AB, B) which do not require filterting on the output before the speakers.

The amplifier you need would depend upon what your application is.  As I recall, your application was relatively low power, and so the amplifier would be chosen on the basis of what form your audio into will be.  If I know that, I might be able to recommend a single monolithic "digital" amplifier for you.  If you have a high power need, then that would be a different answer.

Let me know (a) the format of the input audio, (b) the power level of the output, and (3) something about the final application.  Again, if I remember correctly, the application was related to hearing aids, but I don't know if it will finally be in-ear type, or some other form.    If in-ear,  the noise performance of whatever amplifier is chosen will be very important, along with the power consumption.

Ken

Hi Nate,

The term digital amplifier is one of those terms that can mean many things.  I prefer the following:

All Digital Amp:

This term means that the audio input to the amp is in digital form, usually via a recognized digital audio format like I2S, and that the output is operating in Class D mode where the output signal switches between the voltage rails (+ and - supply, or + supply and GND).  But basically it means that the amplifier should be able to take in digitized samples of the audio at some particular sampling rate, and thru internal means  modulate (usually pulse width modulation) the output switching waveform in some fashion such that IF you applied a low pass filter between the outputs and the speakers, the combination of low pass filter and speaker inductance/capacitance would convert the switching waveform to analog audio you can hear.

Class D amp:

This primarily means an audio amp where the output stage is operating in Class D (switching mode).  Some people refer to this as a digital amp.  But it is really a digital (switching) output stage.   The input can be analog audio, with the amplifier operating a particular A-D modulation scheme which results in the switching output or the input could also be digital as already described, depending upon the particular amplifier design.   Output filtering is general required except in relatively low power cases (generally under 5W, but new designs are pushing the envelope to ~15W) and where the amplifier is physically very close to the speaker (few inches)

Of course there are amplifiers out there that take in digitized audio and do an internal D-A operation and operate the output stage in one of several continuous time analog Classes (A, AB, B) which do not require filterting on the output before the speakers.

The amplifier you need would depend upon what your application is.  As I recall, your application was relatively low power, and so the amplifier would be chosen on the basis of what form your audio into will be.  If I know that, I might be able to recommend a single monolithic "digital" amplifier for you.  If you have a high power need, then that would be a different answer.

Let me know (a) the format of the input audio, (b) the power level of the output, and (3) something about the final application.  Again, if I remember correctly, the application was related to hearing aids, but I don't know if it will finally be in-ear type, or some other form.    If in-ear,  the noise performance of whatever amplifier is chosen will be very important, along with the power consumption.

Ken