Moving the driver closer to the pickup (and end of the tine) shortens time to full amplitude when starting from rest. Other frequencies are amplified and vibrate the tine also, not sure where these are coming from yet. Removing the entire tine/tonebar assembly and turning up the gain shows resonant frequencies of pickup/driver feedback loop - the frequency increases with a decrease in distance between driver and pickup (about 900 Hz with 1 cm separation). Also, Frequency decreases with an increase in gain. Removing the capacitor in the gain stage makes higher frequencies appear at lower gain setting. There appears to be a boundary level in the gain below which these resonant frequencies aren't present.
Les was wondering if the voltage-to-current converter (output stage) would be able to drive a complex load. Loaded with a 10 Ω resistor (same DC resistance as driver) gives a clean output (observed on oscilloscope) but loaded with the driver inductor gives garbage. Maybe need to use a regular power amp?
I'm also wondering about sensing vibrations with piezo pickup to amplify and feed back into the tine in order to avoid the magnetic coupling between driver and pickup in the feedback loop.
ALSO looking for recommendations for free circuit-drawing software...
