I have been having a strange issue with my OB-6 and multiple past OB-6's. In the "-1" Transpose range, certain voices will play notes with the filter completely open when played in the lower end of the keyboard. I had this issue on 2 different modules I had a couple of years ago and now I'm on my 2nd keyboard and it has done it straight out of the box in both instances. It does it irrespective of firmware version, and calibration or clearing calibration and starting over doesn't change it. It also only occurs when keyboard tracking is on "Full" and the filter cutoff knob is in the very low range, regardless of the envelope setting. I'm still in communication with technical support, but am wondering has anyone else encountered this problem? A quick way I've found to see if your unit does it is follow these steps:
1. Initialize patch
2. Set Transpose to "-1"
3. Set keyboard tracking to "Full"
4. Turn filter frequency knob completely down
5. Play notes at the bottom of the keyboard repeatedly, like the lowest E, and see if some of them sound completely unfiltered
Something interesting is that if you set transpose to "0" and tune the oscillator down an octave instead, it doesn't do it. Makes me think it's a software issue, but who knows.