(SUPER) low budget signal generator

[benjamintheyon]

Hello everyone, first post here! I am a budding DIY electronics enthusiast (in other words an EE student), and I'm currently in the process of hacking together a lab bench. I started with converting an ATX computer PSU, and now I need a signal generator.

My first thought was to see if anyone has used an Arduino. It looks like it's been done before, but I wanted to go simpler...and this is what I've come up with:

I'm thinking I'll use a cheapo MP3 player. I can generate a range of waveforms (mostly sinusoids is what I'll need initially), at different frequencies and shapes, and load them onto the MP3 player. Adapt a pair of headphones to plug it into the circuit, and voila! I also have a few scavenged optocouplers and op-amps for protection and scaling, respectively.

I feel like this'll work, but maybe I'm missing something critical. I know of a few disadvantages - I won't be able to truly "dial in" the waveform I want, but rather select from what I have available (and make a new one when necessary). That might slow things down when trying to use it. And also since it is passing through this crappy MP3 player, the waveform may be distorted by its' crappy amp. I'm hoping this won't be all THAT significant?

Please, Wizards of Electro-Hacking, grant me your wisdom!