Jeff Duntemann's Contrapositive Diary Rotating Header Image

May 7th, 2011:

Dell’s USFF Internal Amplified Speaker

DellMiniSpeaker.jpgI bought a Dell Optiplex GX620 USFF (Ultra-Small Form Factor) machine last week, and it came without an internal speaker. I didn’t know the speaker was optional until a machine turned up without one, but a look at my three SX280 USFF machines (built in exactly the same case) showed a very small plastic unit that pulls easily out of the chassis when you lift a plastic tab. It’s wired to the mobo through a conventional 4-pin header. And most interesting of all, it has circuitry on its back.

A look through a loupe showed four solder pads (on the left in the photo above) labeled P5V IN, SPK DET, GND and AUD MONO. These correspond to the red, white, black, and green leads respectively. It took me ten minutes to lash up a test on my Heath ET-3200 breadboard. With 5V on the red lead, common on the black lead, and some sine wave from my audio generator on the green lead, that one tiny little doodad filled the shop with an 800 Hz tone.

I’m pretty sure the SPK DET lead allows the computer to know if there’s a speaker in place; my VOM shows it tied to ground. The IC is almost certainly an LM4871 1.1W audio amp. The National Semi logo is on the chip, and the printed number is RA4871. The Dell part number for the assembly as a whole is Y2298.

I needed to order one for the GX620, so I ordered two, and if I need a subminiature speaker amp for a project, it’ll be in the drawer with my other small speakers, ready to go. $2.69 at the CompuFlea eBay store.