I want to build a resonator that slowly (~3 seconds) decays without a stable oscillation. I've tried using a simple RLC circuit without luck - I've got ~1-2ms decay time at maximum; so, I've turned my attention to active oscillators, particularly to the Wien bridge oscillator shown below.
If I turn the R4 all the way to the right, I get a stable square-wave output; if I turn it to the left, the output shape becomes more and more sinusoidal and at some point it becomes unstable, decaying to silence after some time has passed after an induced by pressing the SW1 button disturbance. If I continue turning the R4 to the left, the decay time decreases; it seems logical, that if I want a decay time around several seconds, then I need to turn the R4 right just up to the point where the oscillation starts.
This solution, however, is impossible to embody in real parts, since even a small change in resistance (due to the temperature change, for example) will put the oscillator in the stable oscillation territory again, which I want to avoid at all costs.
So, my questions are:
- How can the Wien bridge oscillator schematic be modified so that it will be slowly decaying without the risk of a stable oscillation?
- Is there a better way to build a slowly decaying resonator?
I am looking, if possible, for a purely analog solution without inductors and without "cheating" by using a stable oscillator and a VCA to control the slowly decaying signal amplitude.