Pins 1,7 and 8 are not needed. I'm trying to slowly move from Fritzing to Kicad. I'm sure it's a better EDA tool it's not as friendly as Fritzing and the learning curve is steep.
I think you'll find that pin 1 (the output of the first amplifier) is needed. You must mean pins 5, 6 & 7 aren't needed. The unused op-amp should be correctly terminated, not simply left unconnected, which can cause trouble. Configure the unused op-amp as a unity gain buffer, with the input grounded. Connect the inverting input (pin 6) to the output (pin 7) and the non-inverting (pin 5) input to 0V.
I seriously doubt you actually built the circuit as drawn. What is Q2 supposed to do? Its gate is just connected to the source so it will be off all the time.
As drawn, there's no automatic gain control on the oscillator so the signal will either slowly fade away or clip to form a horribly distorted waveform. Perhaps Q2 is supposed to be the gain control.
Why not AC couple the signal from the Wein bridge oscillator to the LM386 amplifier?
It should also be possible to build a Wein bridge oscillator using a single power supply so you can eliminate U3. Heck, I'd consider removing the U1 and using the LM386 to make the Wein bridge oscillator. There's even an example on the data sheet.
http://www.ee.ic.ac.uk/pcheung/teaching/DE1_EE/Labs/LM386.pdf
Hello!
I'm a little bit confused. Let's go by parts...
I wrote that LM386 pins 1,7 and 8 are not needed, not the LM358.
I didn't use the LM386 for a Wien bridge for these reasons:
a) I first began using a LM741 to generate a sinewave and then switched to a LM358.
b) I didn't want anything with a light bulb.
c) LM386 was introduced later in the design as an audio amplifier.
Yes, I'm aware I'm not using the 2nd op-amp in the LM358 based on reason a) and I can't see why it should be a problem. There's an image of the sine wave before going to the LM386 amplifier stage and it's clean.
I decided to use a LM386 to amplify the sine wave because I have read in many websites that a LM358 is not an audio amplifier and It shouldn't be used as one.
Also, I don't fully understand the calculations to build a class ab amplifier with transistors and I didn't want to do it by trial and error. So a low power amplifier should do it easily with less components.
R5 and R6 move the signal above 0V to avoid the transistors could clip the signal. I tested it without the resistors and the sine wave was awful. If I'm wrong I would like to fix that.
Q1 and Q2 was the best way I found to turn on and off the sinewave from the arduino without any distorsion. Arduino pin is always HIGH and switched to LOW when the keyer is touched. If there's a better way, I'll love to learn it.
Yes, You are right, there's no automatic gain control to fade away the signal when it's cut off. I never thought it should be necesary. Perhaps it's a big mistake. I attached an image from the DSO when it happens.
The circuit was built exactly as it's described. I'm sure it can be optimized to be more simple with less components.
First I have to find out how to do the calculations with the proposed circuit and replace the light bulb with something else to get a 800hz sine wave.
In the mean while I would like to find out how to amplify the signal and take advantage of what I've done. Once it's working I'll try to replace the LM358 with the LM368, drop the ICL7660 and leave only one IC.