Holman Is Your Phone’s Best Friend

Let’s get something straight right up front: this isn’t much of an electronics project. But it is a very artistic 3D printing project that contains some electronics. [Sjowett] used an off-the-shelf class D amplifier with BlueTooth input to create a simple BlueTooth speaker with a subwoofer. As you can see from the pictures, woofer is exactly the term to use, too.

The clever mechanical design uses 3D printing and common metric PVC pipe. That’s a great technique and resulted in a very clean and professional-looking build. If you don’t have easy access to metric pipe, you could print the pipes, but it will take longer and might not look quite as good.

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A Class D Amp Made From Scrap

[Boolean90] needed an amplifier for a subwoofer, and had a lot of parts sitting around in a scrap bin. His project, a Class D sub amp made out of scrap, is a great example of what you can build with the right know-how and a very large pile of junk.

With digital logic and PWM chips, a Class D amp is one of the simpler ways to get a lot of amplification easily in an efficient package. It’s really not that complicated; an audio signal is turned into a PWM’d square wave, this is sent out to a Mosfet bridge, and finally out to the speaker.

Most Class D amps have a switching frequency of hundreds of kilohertz to the Megahertz range, but since this is an amplifier for a subwoofer that has a cutoff frequency of about 1kHz, the switching frequency doesn’t need to be quite as fast. [Boolean] is using a 50kHz carrier frequency; it’s more than high enough to recreate low frequencies.

With the completed project, [Boolean] has an extremely loud amplifier that has around 75-150W of output power. The subwoofer is only rated for 200W, but with the volume [Boolean] is getting, this isn’t an amp he’ll be rebuilding anytime soon.