Noise in summing op amp circuit (741)

Thread Starter

sotinam

Joined Apr 20, 2016
10
Hi,

Can anyone please help me to figure out why I have lots of noise in my summing voltage circuit?

I am using summing amplifier to add two sine and square voltages. I am attaching two screenshots of the output signal as well as a schematic of the circuit.

Any help and advice is highly appreciated.

Thanks,
S
 

Attachments

Alec_t

Joined Sep 17, 2013
11,387
Welcome to AAC!
Building the circuit on a breadboard, using long connecting wires, using unscreened signal wires, operating the circuit in an electrically-noisy place, lack of or inadequate supply decoupling, use of a cheap switch-mode power supply can all contribute to noise pick-up.
 

#12

Joined Nov 30, 2010
18,210
Oh my, that is nasty!
You have the signal floating on the power line frequency and a lot of hash and ringing.
Of course, you gave us nothing about the resistance used, the power supply voltages, the biasing method.
Start over and build this nice and tight with good shielding and capacitance right at the chip to help it deliver fast current when it needs to.
 

Thread Starter

sotinam

Joined Apr 20, 2016
10
Thank you guys for your reply. I appreciate that.

Actually I made it better by replacing the power supplies with higher quality ones. The output signal is much better.
I am attaching a schematic of my circuit as well as screenshot of the oscilloscope, and a picture of the circuit.

Would you please have a look at the attached? As you see the noise is much less than before. Any comments on how to make it better (if it is possible)? Maybe moving every thing on PCB and soldering wires will improve the circuit performance?

Thanks again,
S
 

Attachments

#12

Joined Nov 30, 2010
18,210
That looks like a faster square wave riding on a slower sine wave. That's what you wanted, isn't it?
 

ErnieM

Joined Apr 24, 2011
8,045
What does the output look like with both inputs shorted to ground?

What does the output look like with just V1 shorted?

What does the output look like with just V2 shorted?

What does V1 and V2 look like?

These are things you should be thinking of when sitting at your setup to try. Instead of asking us ask your circuit where comes this noise.

You can ask us too but your circuit knows all.
 

Thread Starter

sotinam

Joined Apr 20, 2016
10
Just wanted to thank you guys again. Power supplies were the problem as I said.
Sorry for silly question, its my first time working with op-amps.
 
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