741 wien oscillator

Thread Starter

Alberto01

Joined Jul 9, 2021
13
Hello, i made a wien oscillator with a 741 op amp the problem is it outputs a very narrow and cut off signal that is almost like a triangle wave, you can see it attached in the files.16258612158643879976720104863885.jpg
I have zero idea why it doesnt output a normal sine wave. Im using 10k resistors and 10nf capacitors for the filters loop, a 47k trimmer as the gain loop paired with another potentiometer used as a gain adjuster.
 

Martin_R

Joined Aug 28, 2019
103
The 741 is a very old IC. There are more modern chips available with wider bandwidth and frequency. Try a TL071, dirt cheap and so much better than a 741.
 

crutschow

Joined Mar 14, 2008
28,227
Note that the amplitude and distortion of that circuit is very sensitive to the op amp gain as determined by R2 and R3.
If you reduce the value of R2 in your real circuit, it should reduce the amplitude and distortion.
You may want to replace that resistor with a 100kΩ pot.

Typically such a circuit use some sort of AGC in the feedback to stabilize the amplitude without requiring any tweaking.
 

AnalogKid

Joined Aug 1, 2013
9,502
A wein bridge oscillator circuit is not stable; that is, amplitude stable. It makes a perfect sinewave at a constant output amplitude ***only** with theoretically perfect resistors than you can not purchase. As above, a successful circuit always has some form of feedback based on the peak, average, or RMS value of the output waveform. Search for Wein bridge oscillator circuits to see hundreds of examples.

ak
 

Thread Starter

Alberto01

Joined Jul 9, 2021
13
The clipped waveform shown is differentiated as though it has an output coupling capacitor value that is too small and is feeding a load.
I simulated what I am talking about but my Sim software does not have an antique 741 opamp:
So you suggest adding stronger capacitors in the filter loop?
 

bertus

Joined Apr 5, 2008
21,683
Hello,

It is not the filter capacitors, but the gain control.
Have a look at the PDF's I posted in post #3.

Bertus
 

Thread Starter

Alberto01

Joined Jul 9, 2021
13
Hello,

It is not the filter capacitors, but the gain control.
Have a look at the PDF's I posted in post #3.

Bertus
Nothing here helped, i looked up that it could be the power supply since mine is really shitty, i post the model here.
EVENTEK KPS3010D
 

Audioguru again

Joined Oct 21, 2019
3,872
The highpass and lowpass filters are fine.
I suggested that the horrible waveform is caused by a capacitor-coupled load that you did not show that has its coupling capacitor having a value that is much too low. Your load resistance that also was not shown might be too low.

The basic Wien-Bridge oscillator you show has nothing to control its output level so the output of the opamp is clipping and is producing almost squarewaves. Then the very low value of the unseen output coupling capacitor that I added blocks the low sinewave frequency but passes the high frequency distortion harmonics.
 

Attachments

Audioguru again

Joined Oct 21, 2019
3,872
Diodes? Your schematic is missing the diodes that you talk about. Where are they on the schematic?
Please add the load, its coupling capacitor and the diodes to your schematic.
 
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