741 wien oscillator

Audioguru again

Joined Oct 21, 2019
5,406
Your new circuit with diodes has its load off the screen. I simulated it with a different opamp that makes no difference and I used the load I had before which also makes no difference. I do not see the spikes that you showed.

The diodes limit the output level but they produce distortion. You can reduce the affect of the diodes which also reduces the distortion but then the output level is not regulated as much.
 

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Alberto01

Joined Jul 9, 2021
13
Your new circuit with diodes has its load off the screen. I simulated it with a different opamp that makes no difference and I used the load I had before which also makes no difference. I do not see the spikes that you showed.

The diodes limit the output level but they produce distortion. You can reduce the affect of the diodes which also reduces the distortion but then the output level is not regulated as much.
So i just need to attach load?
 

Deleted member 115935

Joined Dec 31, 1969
0
Can we see a picture of how you have connected the scope to the circuit ?
can we see the scope zoomed in a little more please, so we see may be three cycles

Can you check the scope settings please,
how many volts PkPk is that signal ?
how much above / below ground is that ?

what value do your power supplies come out at when measured on the same scope settings ?

it looks like you have a 150 v signal there !
with a period of around 1 ms,
is this what you are expecting ? or is the scope not set correct ?
or are you not using a 10 times probe ?

Even 15 v is quiet a push for the 741,
depending what its load is ,

Personally I dont know if Id expect a wein oscillator to have a straight line through zero and then a curve at the top / bottom,
I think Id expect a wein bridge oscilator to clip, more to a square wave, with a more flat top,

Its got to be 45 years ago, that I built the heath kit wein bridge osciltaor,
which used a bycicle light bulb to provide amplitude stabalisation,
Im surprised that this desing has no amplitude stabalisation in it,
does it not need it ?

https://en.wikipedia.org/wiki/Wien_bridge_oscillator
 
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Danko

Joined Nov 22, 2017
1,487
Most Caps are +/-20%. If they are not well matched going to have issues. You need +/-1% resistors and +/-1% caps.
With 10n ±20% capacitors C1 and C2 in worst case oscillator works well.
Checked with OP07 and TL072 too.
1625999434145.png
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
@Audioguru again in post above already answered about OP777 (rail-to-rail, not lowers its gain before clipping).
 
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dcbingaman

Joined Jun 30, 2021
789
Dcbingaman, your simulation shows a rail-to-rail opamp. A 53 years old 741 opamp cant doo dat.
True. I retried with an OP07 it still ended up clipping. I tried Danko's circuit above and the oscillations on the output of op amp did not exceed +/-100mV p-p. Not sure what I am doing differently. Danko stated he tried it with an OP07 and it worked?

How do you get a 15V peak signal out of a 741 with 15V supplies?
That is a very good question.

Dcbingaman, your simulation shows a rail-to-rail opamp. A 53 years old 741 opamp cant doo dat.
True. I retried with an OP07 and still had clipping? That was with 100K and 47K gain resistors. With 47K and 28.19K I had oscillation after stabilization but only with p-p of 200mV. Using LTSpice version XVII.

With 10n ±20% capacitors C1 and C2 in worst case oscillator works well.
Checked with OP07 and TL072 too.
View attachment 243163

@Audioguru again in post above already answered about OP777 (rail-to-rail, not lowers its gain before clipping).
Good to know. I replaced it with OP07 and still had clipping, but that was with 100K R2 and 47K R3. Naturally it did not clip at supply voltage but 14V. crutschow had a good question. How is your simulation working at 15V peak when using a non rail to rail output op-amp?

With 10n ±20% capacitors C1 and C2 in worst case oscillator works well.
Checked with OP07 and TL072 too.
View attachment 243163

@Audioguru again in post above already answered about OP777 (rail-to-rail, not lowers its gain before clipping).
Good point. I tried again with OP07 and it still was clipping. Appears my common sense was wrong as well, apparently the caps don't have to be matched for proper operation.
 

Thread Starter

Alberto01

Joined Jul 9, 2021
13
With 10n ±20% capacitors C1 and C2 in worst case oscillator works well.
Checked with OP07 and TL072 too.
View attachment 243163

@Audioguru again in post above already answered about OP777 (rail-to-rail, not lowers its gain before clipping).
I fixed the issue, there was nothing wrong in the circuit but the so marketed dc generator was instead an ac generator that produced a squarewave and was so unfit to be connected to an oscillator
 

Danko

Joined Nov 22, 2017
1,487
I fixed the issue, there was nothing wrong in the circuit but the so marketed dc generator was instead an ac generator that produced a squarewave and was so unfit to be connected to an oscillator
Congratulations!
How do you get a 15V peak signal out of a 741 with 15V supplies?
LTSpice shows that.
With 47K and 28.19K I had oscillation after stabilization but only with p-p of 200mV. Using LTSpice version XVII.
May be you need to update LTspice?
1626024536071.png __________________1626023872506.png
1626020660372.png1626021293884.png1626021589205.png
 

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Alberto01

Joined Jul 9, 2021
13
Right now im probing the + and - of my dc generator and it outputs this thing on the scope, i dont really think i can use it to power a wien oscillator. Does anybody know what is this and why is this happening?20210711_202618.jpg
 

dcbingaman

Joined Jun 30, 2021
789
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?
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

I have been using this supply for good while. I am very impressed with its performance.

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.
 
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