TB303 oscillator

[Daniel Schouten]

Hi All,

Is there anybody on this list, who has ever build a TB303
sawtooth/square oscillator successfully?

I've tried it several times on different PCB layouts, including the
original Roland component layout, but it keeps working instable en very
sensitive. When I'm getting closer and closer in the neighbourhood of
transistors Q25 and Q24 with an object like my finger for example, the
instability keeps on building up. This results in a strange random LF
modulating sound. I can't even measure the waveforms with my scope
because of this great sensitivity.

When I put the oscillator PCB in a metal enclosure, it works much
better, i.e. if I'm not touching the above mentioned transistors or
measuring the waveforms. In my original TB303, you can touch every
component on the PCB without affecting the sound, and that in a plastic
enclosure.    

Most parts I use in the oscillator are original or direct replacement
types, except for the opamp which is an LM358 instead of the AN6562 (is
the AN6562 still available BTW?). In the Roland schematic the FET type
2SK30 has an '(0)' suffix. Does this mean it's a selected version?

I hope someone can help me out with this.

Thanks

Bye,

Daniel