[sdiy] Self-oscillating

[Rönnberg Niklas]

Hi, 
I had an hour left yesterday, so I build the bass drum part of PAiAs Drum
Tone Board. And I ran into some problems...

http://www.paia.com/drumtone.gif

I'm using a bipolar supply of +/-15V, and have connected all +5V (in the
schematic) to ground. In the output stage I use a TL074 and R52 is replaced
with a 6.8K resistor.

Here are my questions:
The Q value (R14) changes the pitch of the cirquit. At low pitches (high
Q?) the cirquit self-oscillates. It self-oscillates about 75% of the Q
setting. It doesn't self-oscillates at the rest 25% higher pitches. How
should I do to have less self-oscillation? I do want to use this as a bass
drum and not as a wood block... :-)
I thought that this cirquit was to be trigged by a +5V puls. Sound at +5V
and silence at 0V (or ground). But it doesn't seem to work that way, maybe
I have done some stupid misstake. Can you help me out by explaining how
PAiA has solved the triggering?

Best regards

/Niklas