I'm working on 741 op-amp summer circuit. I followed the circuits on google.
I did the circuit both on lab and simulation. But the results aren't as expected, I thought it will sum any voltage and add that to the outptut with setting the gain to be 1.
You just got the wrong circuit from Google.
That is not a true summer circuit where all the input voltages are added together.
For that you need to use a resistor in series with each the sources to the (-) input with an equal value resistor from the output to that input (try 10kΩ for all).
Connect the (+) input to ground.
That will invert the signal, so if you want non-inverted, you need to add another inverting op amp at the output of the first.
This is not a useful circuit for a summer and needs Thevenin conversions to make sense.
The "voltage summer" must be inverting as shown already. But you get to choose the Vref point for Vin+ to add to the inverted inputs. That means for positive only inputs and single + supply, you define Vcc/2 as your virtual gnd = Vin+ if you want.
Then the output must feedback to make both inputs matching for a "virtual null" where both inputs match and equal Vcc/2. instead of 0V.
I disconnected the voltage divider and set discrete DC voltage sources, and sent them to the +ve input, with adjusting the gain to unity and it worked accurately
Good.
That works (only) with R6=R7=R8 so for N=3 resistors and then use voltage gain = Av+= N = 1+(R5/R9) = 3
If you wanted more flexibility to choose gains separately without having to change gain for the number of sources. then you would use the inverting inputs only and then Vin+ is a fixed reference. Vref = Vin+ = V+/2 or whatever. Sometimes Op Amps do not work on single supplies near 0V unless specified by Vcm specs.
Choosing between inverting vs non-inverting op-amp configurations depends on your application’s requirements, such as gain and input and output impedance.
I am trying to make sense of the difference between non-inverting and inverting op-amp based audio "mixers". The circuits are basically summing op-amp amplifiers. Here is the part which I...
If you wanted more flexibility to choose gains separately without having to change gain for the number of sources. then you would use the inverting inputs only
Yep, absolutely, I thought the +/-ve inputs of the op-amp are interchangebly for use but it isn't !
I used two configurations:
It seem to be working with almost unity gain.
In the laboratory, it won't be practical to use three or four power supplies to provide seperate voltages to run only one bench.
Also, using a voltage divider is using many resistors, even the students won't understand it.
I think to do this experiment with a good setup, I think using a transformer with multiple outputs with the required DC rectification would fit this application.
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As you already described in post #5, voltage divider is loaded by summer circuit. Using 10k voltage divider resistors makes the effect worse. The experimental setup should focus on demonstration of summer circuit rather than side effects.
This only works with low impedance and clean DC sources. Transformer + rectifier is neither a good solution. I would either use multiple 1.5 V batteries as test sources or a "black box" with multiple buffered voltage outputs.
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As you already described in post #5, voltage divider is loaded by summer circuit. Using 10k voltage divider resistors makes the effect worse. The experimental setup should focus on demonstration of summer circuit rather than side effects.
Yes, that network of the voltage divider resistors would be difficult to reach equal voltages on the lines going to the op-amp for a simple experiment.
If this experiment is very important for the course and future experiments depend on this one, then it's now required to build a more developed setup with much more improved real-world simulation for voltage signals which I think are related to audio applications.
Is that if I disconnect one of the input signals, the output gain changes, so the circuit designer must count the number of the incoming signals and adjust the values of other components accordingly.
This only works with low impedance and clean DC sources. Transformer + rectifier is neither a good solution. I would either use multiple 1.5 V batteries as test sources
Also a good idea, but as the picture I posted in the first post, the laboratory components in a plastic boxes system, I only have the 741 type. So the only way I could think of is developing a voltage divider thinking it might work, but I learned a new lesson of taking out the lines of the voltage divider and supplying them to the op-amp didn't work even with using series 10k resistors which added another implication to the experiment becuase now I must calculate with thevinin theorem each voltage and adjust its resistor circuit to get equal voltage values.
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This worked surprisingly, I don't know why, it's a parallel circuit. Could it be that the op-amp is summing the currents ?
Also, R19, 18, 17 are adjusted according the gain, to get a unity gain. But if I change the value of any resistor, then the output gain changes too. So as I assumed that the voltages and the currents of the input circuit must be set and adjusted to the required output gain.
All the currents that flow in individual inputs flow, in their sum, thru the fdbk circuit.
Keep in mind, because of virtual ground , each input thinks its current is going into ground.
And writing KCL Ir1 = Va/R1, Ir2=Vb/R2.......
Is the OpAmp summing currents ? I like to think its steering them, and isolating them from each
other at the input side.
Not sure why you have R15. Because its got virtual ground across it no current flows thru it, hence
its irrelevant. However there is a small current thru it due to OpAmp input offset V, and G effects,
eg. Aol (open loop gain) of OpAmp finite so virtual ground is not exactly = 0.
Yes, so if like in this situation, I get an inverting voltage in the negative potential and I want it in a positive potential, then I can reverse the output rails and that's it.
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