Just for Fun, I decided to move my wien bridge oscillator from the breadboard to something a little more permanent.
I made a few small modifications:
1) a dual op-amp so that I can use one op-amp to split the power supply.
2) added a couple of DIP switches to switch in and out capacitors to vary the frequency (no, I don't have any dual gang pots on hand)
I did discover something very interesting.
There is a band of instability at certain points where a secondary oscillation can remain. In my case it was an approximately 1Hz variation in amplitude of the output signal.
It causes a modulation of the output that is only completely visible at a very slow scan rate on the CRO. It is both a thing of beauty and horror! I would imagine that the heating and cooling of the filament occurs at around 1Hz. The cure is to increase the overall gain a little.
I might try to get a picture of this from the CRO this afternoon.
I made a few small modifications:
1) a dual op-amp so that I can use one op-amp to split the power supply.
2) added a couple of DIP switches to switch in and out capacitors to vary the frequency (no, I don't have any dual gang pots on hand)
I did discover something very interesting.
There is a band of instability at certain points where a secondary oscillation can remain. In my case it was an approximately 1Hz variation in amplitude of the output signal.
It causes a modulation of the output that is only completely visible at a very slow scan rate on the CRO. It is both a thing of beauty and horror! I would imagine that the heating and cooling of the filament occurs at around 1Hz. The cure is to increase the overall gain a little.
I might try to get a picture of this from the CRO this afternoon.