Schematic review - Colpitts oscillator

Hey Guys,
I’ve been trying to make a Theremin from scratch and have been stuck on the oscillator part for months now. I’ve asked around for help but I haven’t made much progress.

It simulates fine in LTSpice but then it flops in the real world. If some of you fellow wizards could tell me where I’m going wrong that would be great!


Hey Pratik -

Can you move D1 around a bit? I have a hard time seeing the connections there.

It sounds like you are probably not getting enough gain to start oscillating. Offhand suggestion - try dropping Re to zero. That resistor is limiting Q1’s turnon profile to make the gain more stable. Oscillators tend to rely on really high gain. As long as the gain is ridiculously high, the stability doesn’t matter so much.

Hope that helps.

On your actual hardware:

  1. What are you using to look at the output? Where are you probing? Could you be loading down the circuit?

  2. What are the DC voltage on the Base, emitter and collector?

  1. I haven’t built this particular circuit yet but when i did build it I had a Analog discovery with the BNC adapter with the scope probe set to 10X.

  2. Like I said I haven’t built this circuit yet. Will post update when I do

D1 appears to be unconnected on the bottom terminal.