Incidentally, for anyone who's tone deaf or tone hard of hearing, you can use a voltmeter to check the voltages coming out of the sequencer. The semitones should all be 0.08(3) volts apart from each other. I described this in more detail over at http://bytenoise.co.uk/CV%252Fgate as my partner and I were working out how the system works.

If the volts coming out of the sequencer match up with that chart, then the sequencer's fine, it's the oscillator. Use an automatic guitar tuner to tune it if need be.

Hope that helps,
Zoë.