Pulse wave distortion oddity

[drb]

Experimenting with a MIDI keyboard controlling the M32:

1) I set the assign out to CC1 and patched it to the VCA CV in.

2) I found that with some settings of the pulse width and cutoff for the low pass filter I would get a sudden very buzzy sound when setting the mod wheel at 125 or above.

3) After some additional experimentation, I found that only some combinations of the pulse width and cutoff would have this result.

4) Also, only a narrow range of the cutoff would have this result. Turning the modwheel or pulse width higher would not eliminate the buzz, but turning the cutoff higher would (or reduce it).

5) If the VCA mode switch is set to EG with no note being played, the buzz does not occur. If it is set to On with no note on, the buzz occurs. If set to EG and a note is played the buzz occurs. The volume control does not affect the occurance or lack of occurance of the buzz.

6) Most oddly (to me) was the fact that this only happened when turning the pulse width clockwise from noon, not counter clockwise.

Attached are the Mother 32 front panel and a software oscilloscope showing the distortion. Note -- I first heard the distortion with a MIDI keyboard and head phones and no computer.

Is this unique to my unit? Is it an indication of a problem?

Thanks,

drb

[drb]

I contacted Moog technical support about this and they said that it is not a problem with my particular unit. The settings described made the VCA clip.

So no big problem and I still like my Mother-32.

dry