I explained that when your resistor value is low then your capacitor value must be high to produce a low frequency.
High value capacitors are usually electrolytic that has two problems:
1) They are usually POLARIZED (they cannot be used for this AC circuit, they are designed for DC of one polarity only).
2) Their tolerance is very poor (plus and minus 50%) so a 10uF capacitor can be 5uF to 15uF.
The TL071 opamp has an extremely high input resistance so higher value resistors (33k) can be used with non-polarized accurate 0.1uF (100nF) 5% film capacitors.
You forgot to tell us the pwm load on this oscillator that is stopping it from working.
thanks audioguru
you're right so I use capacitors with 10nF ,,, Is TL074 op-amp has an extremely high or low input resistance ???
I know it is low, so that I put a voltage divider at the op-amp output for amplitude control with a double variable resistance,
and it will be the input with triangular oscillation on Lm311 ,thus I have a pwm circuit.
Have you any extra information?
because if I control on frequency using R,R it effect on the amplitude and change it.
The input resistance of the TL074 opamp is provided with junction field-effect transistors. The datasheet says the resistance is ten TRILLION ohms. A trillion is one thousand times one billion.
I know it is low, so that I put a voltage divider at the op-amp output for amplitude control with a double variable resistance, and it will be the input with triangular oscillation on Lm311 ,thus I have a pwm circuit.
If you reduce the value of both of the "R" resistors and add a dual gang pot then this pot can change the frequency. The diodes keep the amplitude constant.
I have a Wien Bridge oscillator that uses a TL072 dual opamp. Its frequencies are from 10Hz to 100kHz. It uses 20M, 2M, 200k and 20k ohms for the "R" resistors that are switched for different ranges and it is tuned 10:1 with a dual gang capacitor from an old AM radio. It uses a Jfet level control circuit and has very low distortion.
The oscillator opamp feeds a 20k ohms volume control that feeds the second opamp as an output buffer.
Hi ,
I want a sin-wave oscillator , when I can control frequency between 5-50 Hz and control amplitude between 1-10 volt ...
the important thing the frequency and amplitude are independent....condition (*)
so if I've change the frequency , the amplitude shouldn't be changed .
i used wien bridge oscillator same as the figure in post #2, but the condition (*) didn't done ...
No.
You changed the opamp and changed resistor and capacitor values. You did not post your latest corrected schematic as you were asked to do.
You did not say how you are changing the RR resistances to change the frequency.
You did not say if the amplitude drops or increases as you increase or decrease the frequency.
You did not say how you measured the amplitude.
You did not say if there was a load.
sorry but there is problem with upload photo ,may the cause is the browser.
I used op-amp tl074 and changed the RR using a double variable resistance
when i decreasing the frequency , the amplitude decreased too.
firstly I measured the amplitude directly , then i put a voltage divider at output terminal
but in tow way if I had change the frequency , the amplitude was changing...
What did you use to measure the output amplitude?
A cheap multimeter is accurate only at 50Hz or 60Hz. It wrongly shows decreased amplitude at lower and higher frequencies. Use an oscilloscope instead.
Maybe your plus and minus power supply is not filtered well.
this is my circuit
I want a sin-wave oscillator , when I can control frequency between 5-50 Hz and control amplitude between 1-10 volt ...
the important thing the frequency and amplitude are independent....condition (*)
so if I've change the frequency , the amplitude shouldn't be changed .
i used wien bridge oscillator same as the figure , but the condition (*) didn't done
The TL074 is a quad opamp with 4 opamps inside. How did you disable or use the other 3 opamps to prevent them from oscillating?
Your circuit is WRONG:
1) R5 and R6 should have exactly the same values and should be a dual potentiometer for frequency adjustment. Each one should have the same value series resistor at one end to limit the highest frequency.
2) R2 should be closer to 2 times the value of R1. Consider if the value of R1 is 5% high and R2 is 5% low due to tolerance.
3) It is better to use lower supply voltages instead of attenuating the output.
this is my circuit
I want a sin-wave oscillator , when I can control frequency between 5-50 Hz and control amplitude between 1-10 volt ...
the important thing the frequency and amplitude are independent....condition (*)
so if I've change the frequency , the amplitude shouldn't be changed .
i used wien bridge oscillator same as the figure , but the condition (*) didn't done
Your problem seems to be that the output amplitude changes when you adjust the frequency, and/or the frequency changes when you try to adjust the amplitude. Im not sure which or both of these are happening. But what you need to show now is HOW are you changing the frequency for example? I think when you change the frequency you need to change TWO components at the same time, like the two resistors that go with the two capacitors, and also to get a wider frequency adjustment you need to switch in or out two different capacitors so you can get a totally different range.
In other words, there is more to it when you want to adjust the frequency. Let us know what you tried already and that might help.
Hi ,
Thanks for your previous help
now , I ask you about the triangular oscillator using tl074
1. about the equations for amplitude and frequency ?
2. how the circuit work and some extra information ?
3. the oscillation' condition
U1A is a Schmitt-trigger. It has positive feedback applied with R1 and R2. The values of R1 and R2 and the supply voltage determine the input threshold voltage at the peak level of the triangle waveform.
U2A is an integrator. Its charging and discharging times are set by the values of R3 and C1.
With a plus and minus 15V supply, the maximum output of a TL07x opamp is about +12.5V and -13.5V. It can make a pretty good triangle wave up to about 20kHz, but to about 50kHz when it has a plus and minus 5V supply.
It takes time for the capacitor to charge and discharge to certain voltages on the ramps of the triangle so the output level also affects the frequency of a triangle wave generator.
The capacitor charging current is determined by the voltage level at the output of U1A in the value of R3. Pin 2 of U2A is at 0V.
Look in Google for the formulas.
The output level of the triangle wave is calculated during the design of the oscillator.
The frequency from this triangle wave oscillator can be higher when the output level is lower because the capacitor charges and discharges for less time.
The frequency from an opamp can also be higher when the level is lower due to its slew rate limitation.
If you want a higher frequency then the capacitor must charge and discharge faster which means the capacitor value and the resistor value that charges it must be smaller.