Workshop 88 member [Jim] got his hands on a couple of SanDisk Sansa Clip+ MP3 recorder/players from Woot, and was anxious to see what he could do with them.
The first order of business was to install RockBox, an open source hardware package built for a wide range of MP3 players. He was impressed with how robust the firmware was, though he thought the Sansa’s built-in microphone could use a bit of upgrading. Acting on a tip from a fellow square dance enthusiast, he disassembled one to see how he might add an external audio input.
He pried the existing mic apart, and desoldered it from the motherboard, installing a small capacitor and resistor in its place. He extended some wires through the case, then powered up the unit to make sure it was still alive and well. Since things still looked good, [Jim] put some audio on the Sansa’s new inputs and sure enough it recorded the audio without a hitch.
He says that his initial guesses for the capacitor and resistor values were pretty decent, though with a bit of tweaking he should be able to get exactly the recording levels he was looking for. Not bad for a $20 audio recorder!
Why add a capacitor and resistor? Doesn’t that make a filter? Wouldn’t that be blocking some frequencies?
The builtin mic is one of those electret type things, and needs a DC bias – but the mic he’s using obviously doesn’t, so by putting the cap in there (in series) it removes the bias.
The resistor is just in there for impedance matching.
Ah….I see now.
The hack is obviously cool, but even better is the rockbox FW, with which my sans clip+ finally is able to play FM radio not just for around 5 minutes. With latest Sansa fw it always froze in FM radio mode. Belive me: really annoying.
Now, if you could get it to do a STEREO line in, I’d be all over it! That’s still just mono.
I’m a concert taper (don’t say bootlegger – I don’t sell) and I’ve been looking for a more discrete recorder (that’s just my mp3 player, Mr. security dude!). Maxell makes a small stereo FM transmitter that’s battery operated. RockBox will record stereo from the radio. I take my powered mic (not plug-in power) jack it into the FM transmitter, and record from the radio in stereo.
Wouldn’t you need to plug in two mics for stereo? Also have two fm transmitters, one over one side of the stage/venue/set and one on the other? How could you get descent signal from both in a discreet fashion to your MP3 player? Sounds iffy to me lol