Rocking Out in Stereo

After installing Windows 98 on the PAC I was disappointed at the lack of noises coming from the box. There is a built-in PC speaker, but Windows does not use this to play sounds. To solve the problem I installed a set of speakers to be driven by the Sound Blaster Live! card that was just installed. The speakers are nothing special; I pulled them from a TV when recycling it a few months back.

To drive the small speakers I picked up a PAM8406 based amplifier. I found this board after searching around for stereo amplifiers for small speakers. This particular board can be set to run the PAM8406 in class AB mode which should have less RF emissions compared to class D mode.

I removed the existing mode resistor and soldered a small piece of wire to set the module to use AB mode. I also replaced the power screw terminals with a 4-pin connector so the module could be connected directly to the PAC’s power supply. The existing wires on the speakers were very short so I replaced them and terminated the ends of the new wires with ferrules.

The easiest way to connect the sound card to the amplifier was to use the rear output of the card to drive the amplifier input. I added a 1/8” audio jack to the card slot cover that had the USB breakouts and wired the jack to a pigtail on the inside of the case. I also added a reset button to the same slot cover because it fit perfectly in the remaining space.

I tried many orientations of the speakers and ended up removing the plastic shroud pieces to make them smaller. After much debating I settled on mounting the speakers to the supports that attach the inner frame of the PAC to the outer plastic casing.

I used a few pieces of double-sided foam tape to mount each speaker. A mechanical connection with a solid adapter might be better, but foam tape has the advantage of dampening vibrations from the speakers.

The amplifier board fit nicely next to the CF-IDE adapter board. I installed it the same way as the other board using several layers of double-sided foam tape. The board has a volume knob, but the maximum volume seems to be the best setting for the speakers I have.

I added a short patch cable to connect the sound card output to the amplifier input. I plan to make this look a bit nicer by replacing the cable with one that has right-angle connectors.

The speakers sit just below holes that help hold the keyboard on. The audio quality is about what you would expect from a small TV: very little bass and a very clear high end.

Once I had everything installed I booted into Windows and was greeted with that sweet 98 startup sound. Initially speakers seemed like a minor addition, but being able to hear the PAC without constantly switching headphones from one box to another is really convenient.