MAKE contributor Michael Una shares his experience hacking the Bliptronic 5000 melody sequencer –

First, I replaced the internal crystal with a Getlofi Precision Oscillator kit.  That was easy, and it’s very responsive. 
[…]
I also found a spot on the audio IC that creates a rich harmonic drone.  I should note here that this bend should be done through resistance- I used a 500k pot and found that the audio would distort and cut out when resistance approaches zero.

More details over at GetLoFi.