Sparkfun Amplifier Kit (and Power Supply Solution)
Look at the size of that heat sink!
The Sparkfun STA540 amplifier kit is a cool, fun to put together amplifier kit that employs the STA540 amplifier chip at the core of the device. The chip itself is a 4-channel AB amplifier chip that can be employed in a number of ways depending on the circuit configuration. The kit is really easy to put together, not because of the included instructions, but because the components are actually labeled on the board. This really is a foolproof kit and a great introduction for the new audio electronics enthusiast. The sonic results of the kit are pretty impressive too. It has a good bang for the buck at 38 watts per channel (2 ch) at 18 V and 4 Ω speakers, and has a low noise floor for an affordable ($30) DIY kit. Additionally, and as evidenced by the picture above, it has a small form factor. That is, despite the enormous heat sink. Holy mackerel! (Okay, the wide-angle lens distorts it juuuuuuust a little.)
One problem we encountered in our testing was that the unit would feed-back at about 5Hz when connected to speakers that required more power. Some net researched indicated that the problem was the power supply. Many solutions were proffered up, but most involved either an expensive solution, or a toilsome one. One person on a board stated that depending on the configuration (including the speakers involved) the kit could require upwards of 3-4 amps. This is high current compared to most 9-12V power supplies. Fortunately I had a 12V 4 amp supply lying around that we could use to test this theory. Sure enough, when powered with the higher-amp supply, the 3-5Hz popping ceased all together.
Our problem with that solution was that we needed to power 4 total amps. This would mean getting three more of these supplies and then carrying around the extra power strip to host them. It would also mean a sloppy, inconvenient mess of wires. In searching for a solution we could not find the required voltage with the required amperage in a multi-channel power supply. Naturally, we decided to see exactly what we needed for our application. Using a multimeter to test the current being drawn with the kit hooked up to our test speakers (2 JBL Model L15 speakers) we found that, at 12V, our circuit only pulled < 0.7 amps. This made the search for a power supply solution much easier, and before too long we found this power supply.
4 channels, 12V 1.5A per channel
This box kicks out 4 channels with 12V 1.5A per channel. After receiving the supply a test quickly proved it solved the feedback problem. The 1.5A per channel is double what we needed for the JBL speakers, which draw more power than we plan to use. At a paltry $29, this power supply was also the most economical. It will power all 4 of our amplifiers (8 speakers!) and is small enough to fit in the amp enclosure. (Upcoming post 😉 )
If you plan on buying one of these kits, definitely hook it up to the system you plan to power it with, test the current it draws, and get a power supply with the appropriate amperage.
Until next time, happy amplifying.