I make kits so I’m always interested in seeing what other people have up their sleeves. For my bike stereo last year I used 2 class-d amps based on the TPA3001D (1 x 20W). This year, I bought 2 AMP3 kits from 41Hz. Each kit drives 2 x 25W which is perfect since I have one speaker on each handlebar. They are designed to run on a 12V SLA battery (up to 14.5V input).

Stuff I liked about the kit:

• Silkscreened, soldermasked PCB for easy assembly
• Lots of thruhole vias, heavyweight copper
• Winding the toroids was totally painless
• Chip works great!
• Has a configurable pre-amp that is good enough to take line-level input

Stuff that was a little annoying

• PCB came with copper shorts, apparently a fluke but still frustrated me
• 0805 parts: Why? 1206 would be much easier! (Jan says the particular resistors were thin film and only available in 0805 although I’m still a little suspicious…)
• Output connection and power connection is adjacent for no particular reason, and holes are much too small for speakergauge wire. I think having large speaker-style terminal blocks for the speaker outputs would be a reasonable design upgrade.
• If you’re going to use 2oz copper, have thermals! Soldering this requires a very powerful iron which also needs to have a fine tip. That’s a bit of an oxymoron.

Overall: I give this kit a B+ Its a great design, with only a few technical issues. At $25 for 2 channels of 25W classD action, its a mega-bargain!

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