Kit Review: AMP3 (41Hz)

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!

Have a suggestion for a kit to review? Comment here or send me email:

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  1. Great post! Would love to see you be a little more active and post more things like this. Maybe even expand it to include neat components that Make regulary talks about, such as the new Sparkfun GPRS+GPS module, etc.

  2. What about sound capabilities ? Is there some noise, what the SNR .. etc ..
    Lot of people think that classD amp sound really bad.

    Bye (and keep on going !!!)

  3. “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.”

    In my day, we soldered uphill in the snow – both ways!

  4. Nice reading your review.

    But this amp is favoured by me for being small and large terminals and larger components is not going to help that. For people who can’t work with tiny parts there’s AMP6 which is entirely through hole. Today there’s an even smaller AMP32, it uses ready made coils, so no winding necessary.

    The speaker outputs from the chip are not any bit thicker than the wire that fits in these terminals so is by all means sufficient.

    What I find most important is that it sounds very good, not only for the size. It is extremely low noise and low IMD, sound is neutral and precise. Even low frequencies are represented powerful yet dry. It has more resolution and staging than almost any other amp.

    All the amp32 amps I’ve built still work. I’ve built 28 of them and did the first one more than a year ago…

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