TDA7492 Class D 50×50 AMP

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If you are reading this in the Midwest US then you know how crazy hot it has been lately. It’s supposed to be Fall and it hit 90 degrees today in Toledo! Well there is one thing that goes with good weather and that is hanging outside, and what goes better with hanging outdoors than music? Ok.. The argument could be made that beer is a better answer, but I didn’t make beer (although I do homebrew!) But that is another post for another time.

So one of my first projects when buying a house was that I wanted to have multi-room audio. Not only did I want to have speakers in every room, but I also wanted to be able to play different things in different rooms, or even sync up music between certain rooms. I know what you are thinking, doesn’t Sonos do that? Yea, for like $500 a pop, for the cheap unit. I know we can accomplish the same thing, and not only for cheaper, but since we are doing it we can customize it. Enter the Logitech Media Server, PiCorePlayer, and our TDA7492!

Schematic


Looks like fun doesn’t it? Essentially you have your line inputs on the left, power and speaker outs on the right. The cool thing about this amplifier is that depending on how much DC voltage you put it, that is how much power goes to the speakers.

Specs:

  • 50 W + 50 W continuous output power at THD = 10% with RL = 6 Ω and VCC = 25 V
  • 40 W + 40 W continuous output power at THD = 10% with RL = 8 Ω and VCC = 25 V
  • Wide-range single-supply operation (8 – 26 V)
  • High efficiency (η = 90%)
  • Short-circuit protection
  • Thermal overload protection

All that and for less than $10.

Construction


So I had an unused power supply that was 19V and 3.5A. Perfect! So I grab a handy dandy Project box and begin to set it up. I drilled a hole in the top so that it could get a little air. I had to sand down the insides to get the amp board to fit inside with the box lid. A quick solder of the RCA cable to an unused headphone chord and we were in business.

I cut some holes (not pictures, I know, I’m still working on documenting my builds!) on the side for the cables. I use quick disconnects on anything that is screwed into PCB boards so there is no stress on the actual connections.

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Raspberry Pi

Now that I had the amp on the inside, why not put the Raspberry Pi on top? Here is the final product. Thanks to some plastic stand-offs it came out pretty good.

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Conclusion (and one caveat)


The build came out really really well! I was getting a really good signal out, and the speakers sounded really good! There was only 1 issue. I was getting some buzz when there was nothing playing. As anybody that has worked with amps before, this is usually caused by noise on the input like. Since, like the name suggests, the amplifier takes the input and amplifies it. So if you have a noisy input then it’s going to be a noisy output.

To fix this I used a few 2k resistors and soldered them on the line ins. This cured my buzz! I can control the audio from the raspberry pi line and the speakers sound great!

Multi-room audio Links


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