Hi all,
I am a physics student who started to dabble in electronics two years ago. I have built myself my own lab tools including a wicked cool power supply (at least I think so) and a low distortion sine wave generator.
The later was based on the circuit of figure 3.4.11 of http://www.learnabout-electronics.org/Oscillators/osc34.php. It worked (38 dB of contrast between the FH and the SH according to the FFT on my scope) very well but was limited in bandwidth because of a poor opamp choice (a 741: I realised ''industry standard'' does not mean ''appropriate for all circuits''). I also used capacitor rated for 1.6kV (for some reason I still can't figure out) and an unsuitably very slow rectifier diode rated for 1.5A.
I thus decided to upgrade my trusty sine wave generator now that I had a better understanding of opamps, FETs and diodes. I changed the op amp to a TL081, the diode to a 1N914BCT, and the capacitors to acceptable voltage tolerances. I also tried to reduce the number of long wires in my enclosure and reduced the time constant of the AGC circuit to match that of the aforementionned reference....
The result was very disappointing: the oscillator only works when the dual potentiometer is in one of its extreme positions! If it is in one of these positions, I can instantly change the frequency by changing the values of the capacitor pairs (using a switch) without a problem. However, as soon as I change a tiny bit the position of the pot, the oscillations stop!
The reference suggests that a badly matched dual potentiometer may cause these problems. How bad is bad? How can I know if I have a decent enough potentiometer? Is there any you would suggest?
Thanks a lot!
I am a physics student who started to dabble in electronics two years ago. I have built myself my own lab tools including a wicked cool power supply (at least I think so) and a low distortion sine wave generator.
The later was based on the circuit of figure 3.4.11 of http://www.learnabout-electronics.org/Oscillators/osc34.php. It worked (38 dB of contrast between the FH and the SH according to the FFT on my scope) very well but was limited in bandwidth because of a poor opamp choice (a 741: I realised ''industry standard'' does not mean ''appropriate for all circuits''). I also used capacitor rated for 1.6kV (for some reason I still can't figure out) and an unsuitably very slow rectifier diode rated for 1.5A.
I thus decided to upgrade my trusty sine wave generator now that I had a better understanding of opamps, FETs and diodes. I changed the op amp to a TL081, the diode to a 1N914BCT, and the capacitors to acceptable voltage tolerances. I also tried to reduce the number of long wires in my enclosure and reduced the time constant of the AGC circuit to match that of the aforementionned reference....
The result was very disappointing: the oscillator only works when the dual potentiometer is in one of its extreme positions! If it is in one of these positions, I can instantly change the frequency by changing the values of the capacitor pairs (using a switch) without a problem. However, as soon as I change a tiny bit the position of the pot, the oscillations stop!
The reference suggests that a badly matched dual potentiometer may cause these problems. How bad is bad? How can I know if I have a decent enough potentiometer? Is there any you would suggest?
Thanks a lot!