Cirrus Logic DAC
Planet Fox > Electronics > Hi Fi PC Speakers


PC speakers are terrible. You can go out and spend ten bucks on some cheapies that sound like crud, or you can go out and spend a couple hundred bucks of a big bunch of cheapies that sound like crud. Manufacturers making PC speakers seem to think more = better, regardless of the actual quality. I've also never been a fan of their aesthetics, old PC speakers were always beige and looked vaguely like medical equipment, while newer models look more like something you would use to clean the toilet on a flying saucer.

The Design

Honestly, this started out as a way to use some old interesting parts I had laying around, but as usual I got kind of carried away. These things are going to be sitting on my desk all day staring me in the face, I really wanted them to look nice, stately, elegant, and I also wanted them to sound "pretty good" . I don't listen to music on my computer that much, but when I do I want to be able to hear every detail. I also didn't want to spend a lot of money. The design I eventually settled on is a two-way hybrid sealed box/bass reflex cabinet made of MDF laminated with a real wood veneer. A nice extra feature is a headphone jack with a builtin headphone amplifier with its own volume control.

Cabinet Construction

I started out by gluing the veneer (in this case, a very thin lauan plywood) over a 2×4 foot sheet of particleboard. After I cut out the panels the outer dimensions ended up being 12" H/4"D/4"W. I mitered the corners at a 45° angle and glued them with a super strong wood glue, and added little triangular pieces of particle board to the interior corners to help stabilize things. Having one of those ratcheting strap clamps really comes in handy when you're building any kind of box, since it applies pressure from all sides. I left it clamped for about 24 hours and went off to work on other things.

The front baffle is machined from a solid piece of particleboard. I drilled out 3" holes for the drivers with a hole saw, then used a router to smooth down the rough edges. I used the router to chamfer the outside edge at a 45° angle, since it looks nice that way. I used a router to carve a 2×3 inch recess about ¼" deep at the bottom of the right panel where the volume controls and headphone jack will go. This is also when I painted the front baffle black, to keep it from showing through the sheer grille cloth.

I salvaged the drivers from a couple of pairs of really old computer speakers, one pair I got from an old Boston Audio set, the other came from an ancient set made by a company named Labtec. If you're building a pair of these for yourself I would suggest looking in to some of the great 3" full-range drivers they have at Parts Express. The drivers I had didn't come with any kind of mounting holes, so I just glued them on with a ton of industrial grade hot glue, and since I had the glue gun out I reinforced the cabinet corners some more.

With the drivers mounted to the front board I could set the grille cloth. The grille cloth I used isn't anything fancy, just sheer black spandexy type fabric you can find at pretty much any fabric store. I gave the front panel a quick dose of spray glue to help keep things in place (protect the drivers with cardboard discs). If you're using the right kind of spray glue, it should be tacky and hold on to the fabric, but still allow you to reposition it. The hardest part is simultaneously stretching the fabric tight and stapling it to the back of the panel. You have to make sure you get it stretched really tight, and put a ton of staples in it, or it will sag eventually and there's no easy way to fix that.

The cabinet was done setting and still needed a lot of work. I filled in any tiny gaps near the corner joints with stainable wood putty and gave the whole thing a good sanding with 220 grit sandpaper, followed by #0000 steel wool. I stained it using Minwax 210B Cherry oil-based stainand let it dry overnight. The next day I applied about four coats of high gloss lacquer, rubbing it down in between coats with #0000 steel wool to remove the little lacquer particles that harden before they can stick to the wood, followed by a tack rag to pick up any dusty residue. Since lacquer dries almost instantly I went ahead and polished and buffed it with SC Johnson paste wax and an orbital buffer.

The final steps involved in putting the cabinet together were gluing the front panel to the cabinet with more industrial strength hot glue. I installed a particleboard baffle in the cabinet between the top and bottom drivers to separate them, since the top driver's enclosure will be sealed, and the bottom will be ported. The back panel is just a plain piece of particleboard painted black, sized to fit snugly inside the back of the cabinet. I drilled a 1" hole about 2" up from the bottom, this will be the port for the lower driver.

Look at what I found

Like all my projects, I did this point-to-point on perfboard. There were two integrated circuits used in this design - a Samsung KA2206 2.6W audio amplifier for the speakers, and a Samsung KA2209 low power amp is used for the headphone amp.
Considering I designed these in 2011, that seems like kind of a strange choice, right? Those chips are both out of production (although you can cross reference them for other chips quite easily) . Interestingly enough, it was a "found" KA2206 that started me on this project. Back in 1989 my parents got me a little Lennox Sound boombox, it was really nice and I carried it all over the place, listened to thousands of hours of tapes on it. It went missing some time around 1993 and I didn't see it again until I was clearing out a backyard brush pile in the fall of 2008. My poor little boombox, what was left of it, had been lost in the brush pile for around 15 years (Along with something else on this site that I fixed). All those years of rain and cold and heat didn't do it any good, the circuit board was cracked in half and the case was full of dirt and wet leaves. It would never work again, or so you would think.
I salvaged all of the components from it, capacitors, resistors, some integrated circuits including a Samsung KA2206N amplifier, Daewoo FM IF frontend, and Sanyo LA3161 tape head preamp, and even the tape head. Most of the components, save for the potentiometers, still tested within tolerance and after hosing out all of the dirt they still looked OK, so I neatly bagged them up to save for a future project. They sat in my parts bin until 2011 when I was dismantling some broken PC speakers and noticed they were powered by a KA2206B (same as the N, but with pins 4,5,12, and 13 fused into a cooling fin). Oh, that's what I'll do, I'll make some PC speakers with those parts, I thought to myself.
But would a 22 year old chip that had spent 15 years out in all kinds of horrible weather actually work? I went ahead and built the application circuit with a DIP socket, so I could change out chips as necessary, and ordered an NTE1667 chip, which is a pin for pin substitute for KA2206. My circuit turned out alright, and the NTE part was working fine, I also tried the KA2206 I found in the computer speakers and it worked fine as well, now for the moment of truth. I plugged in my old weatherbeaten KA2206 and slowly powered it up, and it actually worked! In fact, it sounded even better than the new part. The full assembly included the old KA2206, a few of the salvaged electrolytics and a pair of salvaged film caps, as well as the headphone jack and power LED. All of these parts are now 25 years old, 15 of which were spent outside, and I've been using them every day for the last three years. Is it my imagination or were things made a lot better in the 80s?

Finishing up

I mounted the volume controls, headphone jack and power indicator on a piece of plexiglass painted black on one side and glued this into the recess I made earlier. The board containing the amps was mounted to the inside floor of the cabinet with some plastic standoff and I wired everything up. I left a flying lead with a 3.5mm plug for connecting to the computer, and installed an RCA jack for connecting to the left speaker and DC power jack. I used small self-drilling screws to secure the back in case I want to make any changes later. The whole thing runs off of an old Sega Genesis 9V plug-in transformer I had laying around. I am very pleased with the overall results, and since I see and use these every day, they've become one of my favorite projects, and they even hold some sentimental value due to the provenance of the parts.

Yes, I have at least one orange room in my house. Like you don't.

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