This project is based on the Parts-Express 2.1 amp board, Part # 320-608. As I saw this on the website and observed it’s specs — 15 watts for each of the stereo channels, and 30 watts for the subwoofer section — I wondered if it would work as the amp in a very small plate amp. After getting some positive feedback from the folks on the Tech-Talk board, I decided to design and build it, hoping it would produce decent sound in a ‘micro’ form factor.
It is a true plate amp, although much smaller than any I’ve ever seen before… at 4″ square, and only a few inches deep, it will fit in almost any speaker you can imagine, but still deliver clear, powerful output to any small/medium 2.1 speaker system.
I wanted this project to be able to fit into even the smallest of speakers, or a subwoofer, so it needed to be sturdy and airtight. I also wanted this amp to be able to play loud enough with most speakers to provide rewarding music quality, but to also be completely hidden out of the way.
Additionally, I wanted this project to be very good looking, so I used an aluminum plate as the foundation for this project and paid extra attention to the small details… and tried to come up with an attractive layout for the components as viewed from the rear. I also wanted to use all Parts-Express components if possible.
There are a total of 8 components that need to fit on the aluminum plate, and the plate that Parts-Express sells comes pre-punched with two notched holes, so I had to get creative to work around and with those existing holes. After designing and building several prototypes, I came up with a design that allowed all the components to fit on the plate with enough space around them to operate correctly. The two knobs for the subwoofer volume and main volume are probably the closest, but can still be easily adjusted individually.
A PDF is available with full instructions as well as a template that you can tape to the aluminum plate, which when center-punched — will show exactly where to drill the holes for every component.
Each component is mounted with clear silicone to act as a sealant against air leaks, and the threads of each component are sealed with blue thread-locking compound to prevent them from loosening over time from vibration. I protected the aluminum plate from scratches with blue painters tape, and I cleaned the plate as I built it with alcohol and cotton swabs to keep the aluminum looking pristine and beautiful.
Tips & Tricks:
My first prototypes, and even the bare amp board seems to be susseptible to noise interference, especially in the bass, “.1” section of the amp. Hooking up the potentiometer to adjust the subwoofer made the noise issues worse. Looking for a solution, I received some good advice from the knowledgeable folks at the Parts-Express Tech-Talk board on how to reduce/eliminate these issues. First, I braided both the input and subwoofer level lines that are soldered to the amp board. This reduces their ability to act like an antenna and helped tremendously with noise. Also, I changed the amp potentiometer from the more commonly used 50k audio taper type, to a 10k audio taper potentiometer, and this helped to reduce noise as well. In the end, I can still occasionally hear a tiny bit of noise at various volume levels on the sub section only, but only in between songs and only when my head is right next to the subwoofer. Basically, the noise issues have been fixed, thanks to some good advice. Still, this amp board will pick up a bit of noise occasionally from nearby electronics or power supplies, for example, so be aware of that.
Also, regarding construction, I’ve built 6 or 7 of these plate amps so far and have broken several of the power switches and melted a few of the 3.5 mm stereo input jacks, so I would strongly recommend that you purchase two of each of these, they are inexpensive and it would be a shame to be almost done building this project and not be able to finish because of waiting for a $2.00 part to arrive in the mail.
Actually, the biggest tip I can suggest is to follow the PDF of the directions closely — there are pictures that detail each step and make construction almost fool-proof. I follow these directions now for each one I build and have no issues whatsoever.
After building several of these plate amps, I have found them to be good sounding, and forgiving of low impedence loads. The specs suggest 8 ohm loads for both the stereo section as well as the subwoofer, but even with prolonged use at high volumes, I have found this amp board to run fine and cool with 4 ohm loads as long as the voltage stays at 16 volts. Using the maximum recommended 18 volts input may cause problems and I haven’t tested the board with anything higher than 16 volts, so I’m recommended you stick with 16 volts as the max.
In testing, I’ve used this amp to power anything from a set of Quark’s, to Neo Nano’s to Overnight Sensations, to even a larger set of D-3’s… and subs from the Voxel subwoofer to a larger Titanic MK2 subwoofer, and it had no problems or issues running any of these. Of course, because of the highish crossover frequency for the lowpass subwoofer section, smaller subwoofers will probably sound better; I’d suggest no larger than 5-6 inches or so, unless facing down — where upper-bass leakage will be less noticeable.
If you can follow the detailed directions and have 2-3 hours of free time and feel like building your very own 2.1 plate amp, this project will stealthily power a set of small to medium sized speakers and a small subwoofer very nicely, and you will have the satisfaction of knowing that you built it yourself.
About the Designer:
I’ve been interested in quality sound and building speakers
since childhood, starting when my father and I gutted the
speakers from an old stereo console unit and mounted them
in a few old wood boxes. Since then, I’ve built dozens of
speakers, subwoofers—and more recently—a few amplifiers.
I find it enjoyable to push myself to learn new things and
design and build ever more challenging projects!
Project Parts List: