Build a Low-Cost, High-End Class-D Amplifier | Hacker News Reader

Build a Low-Cost, High-End Class-D Amplifier

spectrum.ieee.org

38 pointsnaish6 comments

Class-D amps aren't a common project for the electronic enthusiast: although the theory of the Class-D amp is beautiful and simple, there are a lot of details in the construction that are hard to master. Using an evaluation board, as the author does, is a good answer to the problem.

I agree. The author just picked up a reference design kit. It's a whole different matter to design the circuit itself. Picking the right MOSFETs, gate driver IC, feedback system are crucial to great performance. I'm not an audiophile but I know a great Class D engineer/audiophile who's designed a system with a THD+N of 0.003% (The Zetex amplifier the author chose has a THD+N of just 0.1%). It's cool to hear the engineer talk about the "color of sound".

[Addendum] THD+N is a measure of the purity of the output i.e how well the amplified audio signal matches the smaller input audio signal that's fed into the amplifier (from a CD player for example). So the lower the number the better. Typically, the amplifier circuit itself adds some distortions and noise to the actual audio signal. For example, if you fed a pure 1V 1kHz sine signal into the amplifier, your output might be a 20V 1kHz sine wave but with additional signals mixed in. These signals will include inherent noise generated by the amplifier and harmonics generated by the switching nature of the Class-D amplifer (if you look at your audio signal at the output of the MOSFET switches and before the low pass filter, it will look like a square wave or more specifically, a PWM).

http://en.wikipedia.org/wiki/Total_harmonic_distortion

I have to say I was a bit disappointed to find that the author "built" the amp by assembling evaluation boards in a case with a power supply.

$500+ is allot of money to pay to "do-it-yourself" when amps like the T-Amp produce similar power output and are available for 1/10th the cost.

I bought this kit: http://tubedepot.com/diy-k-8ls.html a few weeks ago and planning to start building it this weekend, time permitting. It's got vacuum tubes and requires soldering. I want to run the audio out of my desktop Ubuntu machine through it.

Disclaimer: I do consulting work for TubeDepot.

I think it's cute that this on the the front page of Hacker News. I think it's confusing that it was published in an IEEE publication, rather than a hobby mag. There was no engineering involved in this, nor any real audio knowledge. That's OK. Not everybody can be an expert at everything, but it was puzzling to see it in IEEE.

I think it's great that this guy is building something with his son, and I liked that he linked to Octopart.com, which is an amazing resource that I wish I had known about years ago.

Wired had a nice little article on class D amps:

http://blog.wired.com/music/2008/07/class-d-amplifi.html

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