741 wien oscillator

Danko

Joined Nov 22, 2017
1,493
Thanks, could you send me a link to a dc bench generator that i could use for op amp circuits and that isnt too expensive?
Cheapest way is to buy couple of power supplies like you already have.
You can combine them, for example, as ±15V and +5V or 3.3V and so.
https://www.amazon.com/s?k=lab+power+supply&crid=3126QMSYII8RS&sprefix=Laa+Power+Supply,aps,365&ref=nb_sb_ss_sc_1_16
Interesting, I have the same circuit using LTSpice and it generates saturated semi-square wave after it stabilizes from power on. I used an OP777
More gain of opamp - more precision tuning:
1626037655931.png
ADDED:
Attached is my asc using OP07:
Your asc, tuned:
1626042923353.png
 

Attachments

Last edited:

dcbingaman

Joined Jun 30, 2021
807
To be honest, if you are heavily into electronics a cheap bench power supply is not worth it. I would recommend a Korad 3305D available from digikey:

https://www.digikey.com/en/products...791?s=N4IgTCBcDaINIHkBKBBAIgAgMxYAwFY0QBdAXyA

Consider it a one time investment. It should last your entire career and work for all applications with no hassle. Not to mention you can adjust the maximum current and you can run it in constant current mode if you want a current source instead of a voltage source.

This is a linear power supply not a switching power supply. I would not recommend a switching power supply if you are developing analog circuits. Switchers are cheaper and the output not as good as a linear.

This one produces two variable outputs and one fixed 5V output.
Cheapest way is to buy couple of power supplies like you already have.
You can combine them, for example, as ±15V and +5V or 3.3V and so.
https://www.amazon.com/s?k=lab+power+supply&crid=3126QMSYII8RS&sprefix=Laa+Power+Supply,aps,365&ref=nb_sb_ss_sc_1_16

More gain of opamp - more precision tuning:
View attachment 243226
ADDED:

Your asc, tuned:
View attachment 243246
Nice. Thanks. But is this realistic? I mean if we have to tune R3 to better than 0.1%? Changes in temperature alone could effect the thing?
Example: I changed R3 from 78.35K to 78.4K that is only a 0.06% change, and it started clipping at the top.'

Another example:
Changed R3 back to 78.35K, changed C2 capacitance from 8nF to 7.8nF that is a mere 2.5% change, circuit clips significantly.

This means every single circuit built would have to have custom tuning done and then with changes in temperature you better have resistors and caps that have extremely low ppm/C.
 
Last edited:

Danko

Joined Nov 22, 2017
1,493
Nice. Thanks. But is this realistic? I mean if we have to tune R3 to better than 0.1%? Changes in temperature alone could effect the thing?
It is why we should use Automatic Gain Control system, which monitors V_out and change "R3" or "R4" for V_out stabilization.
Timing caps and resistors define frequency only. AGC controls value of V_out, does not matter what is cause of V_out changes, result - stability of oscillation.
Changes values of timing elements will change frequency only. R3 and R4 not affect on frequency, if V_out is stable.
Changed R3 back to 78.35K, changed C2 capacitance from 8nF to 7.8nF
R3 resistance change can not change capacitance of C2 at all.
------------------
PS. About Power Supplies - when I was typing recommendation for Alberto01, I did not see your post about.
 
Last edited:

Thread Starter

Alberto01

Joined Jul 9, 2021
13
Your scope hookup is wrong. Try using one channel with the ground tied to the power supply negative. For safety use x10 probe.
After i tried this my scope reads a dc signal, maybe i have been probing wrong with the scope my circuit, how should i hook up the probe to the output?
 

BobTPH

Joined Jun 5, 2013
6,086
After i tried this my scope reads a dc signal,
What did you expect the output of a DC power supply should look like?
how should i hook up the probe to the output?
The answer is right in the text you quoted.

If you want to see the ripple or noise in the output voltage, use the same connection, but use AC coupling and turn up the gain.

Bob
 

Thread Starter

Alberto01

Joined Jul 9, 2021
13
What did you expect the output of a DC power supply should look like?

The answer is right in the text you quoted.

If you want to see the ripple or noise in the output voltage, use the same connection, but use AC coupling and turn up the gain.

Bob
I dont know if i hookup positive and ground of the power supply my scope senses a square wave, thought i was doing something wrong
 

dcbingaman

Joined Jun 30, 2021
807
I dont know if i hookup positive and ground of the power supply my scope senses a square wave, thought i was doing something wrong
For any measurement you make with a scope, you want the ground lead tied to the circuit common ground and the signal you want to look at connected to the point of interest of the circuit. In general you should always have the scope probe on x10 mode. This causes less loading on a signal that has high impedance. You can also look at the timing relationship between two signal using two probes. Both probes grounds should tie to the circuit common ground and then each probe to the point within the circuit that you want to measure.

Safety consideration:
NEVER try to look at 120VAC out of power outlet or 240VAC with a scope. In this situation if you do not get the scope probe ground connected to the neutral wire you will literally short out the hot to ground and possibly damage something. If you are checking an outlet always use a battery operated DMM to measure the AC.

Examples:
GoodProbeConnections.PNG
 
Last edited:

BobTPH

Joined Jun 5, 2013
6,086
I dont know if i hookup positive and ground of the power supply my scope senses a square wave, thought i was doing something wrong
It is a bit hard to make sense of that statement.

Are you saying your oscilloscope shows a square wave, or you expected it to show a square wave?

Bob
 

dcbingaman

Joined Jun 30, 2021
807
After i tried this my scope reads a dc signal, maybe i have been probing wrong with the scope my circuit, how should i hook up the probe to the output?
Another word of advice that will keep you from pulling out your hair when troubleshooting. When a signal does not look correct always suspect the scope probe first. Test your probes for proper operation. A lot of scopes put out a low frequency square wave of known amplitude. You can connect the probe to that point and verify the square wave on the display has the correct amplitude. A lot of times the probe 'hat' is not fully engaged into the probe. Make sure the 'hat' is pushed all the way into the probe. If your scope does not have a reference square wave output, you can simply connect it to a DC voltage source from a power supply, verify you see the supply voltage on the scope. It is a good idea to test your probes at regular intervals. Always take good care of your scope probes and only use high quality probes. A scope is technically only as good as the probes it is used with.
 
Last edited:
Top