LM741 connections with signal generator

[Gazmon]

Hi

I have made a basic LM741 op amp circuit to test with my oscilloscope , I will supply my 741 at pins 7 and 4 with 9volt dc -+ supply’s
P
My question I want to use a sine wave from signal generator as my input signal at pins  2 and 3

Will this be ok? What settings would be advised as do not want to damage my sig-gen

Thanks
Gazmon

[Cliff Matthews]

Post the circuit diagram, we don't use crystal balls..

[Audioguru]

1) The 741 opamp design is 53 years old and was designed to use a 30V supply. Some do not work with a 9V supply. They have trouble at frequencies above 11kHz.
2) You NEVER feed both inputs of an opamp with the same signal.

[Gazmon]

Apologies it’s 15 v DC - and+

And aware that you don’t use the same signal for both inputsl, really just hoping for advice about using my signal generator at the inverting ang non-inverting inputs please

I have attached the circuit

[alsetalokin4017]

Don't be deterred from experimenting. You won't damage your function generator as long as you keep to the schematic you posted and don't try to feed 30 volts into the FG!
You could put a small capacitor in series with the input to protect the FG from any DC backflow kind of errors. And there are circuits which feed the same signal to both inputs of an op-amp or comparator, at least some of the time. Experiment! Connect your oscilloscope to the output of the op amp (the "zero volts" level between +15 and -15 is your "ground" for scope and signal generator) and feed various signals into the inputs and see what happens at the output, using two scope channels, one for the input signal and the other for the output signal. Have fun, your chances of letting the magic smoke out of your signal generator are very small.

[iMo]

This is how it works.
The 10Meg is the internal impedance of your oscilloscope probe (10x setting).
Use at your own risk.

[Gazmon]

Don't be deterred from experimenting. You won't damage your function generator as long as you keep to the schematic you posted and don't try to feed 30 volts into the FG!
You could put a small capacitor in series with the input to protect the FG from any DC backflow kind of errors. And there are circuits which feed the same signal to both inputs of an op-amp or comparator, at least some of the time. Experiment! Connect your oscilloscope to the output of the op amp (the "zero volts" level between +15 and -15 is your "ground" for scope and signal generator) and feed various signals into the inputs and see what happens at the output, using two scope channels, one for the input signal and the other for the output signal. Have fun, your chances of letting the magic smoke out of your signal generator are very small.

You mean a capacitor in series connected to the positive line of my FG or both pos and neg leads?, something like 100uf?

[iMo]

@Gazmon: I would highly recommend you to download the LTspice simulator. It is free and pretty easy to work with.
You have to learn to work with it when you are interested in electronics. It helps you simulate your schematics and your measurements before you do in real HW.

[Zero999]

Since the LM741 is powered from a bipolar power supply, the input and output capacitors are unnecessary.

[Gazmon]

What’s easiest way to get a 15v negative power supply or can anyone provide a schematic I can build easily

Thanks for the help

[iMo]

Better start a different topic on -15V provided you have searched for it and have not find a suitable schematics..

[Zero999]

What’s easiest way to get a 15v negative power supply or can anyone provide a schematic I can build easily

Thanks for the help

My advice is don't. If the signal is AC, keep the capacitors, bias the non-inverting input at half the supply and connect R1 to 0V, via a capacitor.

What's the lowest frequency? You might need to increase the capacitor vales. I've changed them to polarised, just in case you want to use electrolytic.

[Gazmon]

Better start a different topic on -15V provided you have searched for it and have not find a suitable schematics..

Sorry for the basic questions here , just wanted to check a few things ,
From you schematic

Vop+ Connection on the Lm741 what’s feeding in here?  , the non inverting - connection on the Lm741 is connected to ground via R1, so there’s no 15v negative  dc - needed here ?

[iMo]

In my first schematics you need two voltage sources, Vop+ and Vop-. The GND (ground) is in the "middle" of both sources.

The input and output is referenced against the GND.

There is the version from Zero999 - where you are using only a single voltage (Vop+ .. GND) while you create "a virtual GND" through the two resistors.

You may take two 9V batteries and play with the 741. See below.

In a schematics, when you have two independent pieces of wire labeled with the same "name", like the couple of short wires labeled "Vop+", it means the wires are connected together. People use this in order to not mess with a lot of long wires in the schematics.

[Gazmon]

Can I substitute the LM741 for an LM358

[Zero999]

Can I substitute the LM741 for an LM358

Yes and no. If you've already designed the PCB, then no, because the LM358 has a totally different pin-out and it's a dual, rather than single op-amp.

If you're just breadboarding or are designing a new PCB, then yes. The only thing you need to be aware of is the LM358 has a class B output stage, which can cause cross-over distortion and is more evident at higher frequencies and gains. This can be eliminated by adding a resistor from the output to the negative power rail, to ensure only one output transistor is conducting, thereby causing it to operate in class A.

https://electronics.stackexchange.com/questions/341843/adding-a-resistor-to-reduce-crossover-distortion-in-an-lm324-lm358


Neither the LM741 nor LM358 are great for frequencies above the the mid-audio band. The TL072 and NE5532 are common, faster op-amps which are much better and commonly available. Try a range of different op-amps and note what happens, as the frequency is increased.

[Gazmon]

Cheers

All Excellent info

[Gazmon]

Can I use 2 x 9v battery’s connected togeather to get a positive/negative voltage of 18v to power the LM741?

Will 18v be ok ?

[basinstreetdesign]

Can I use 2 x 9v battery’s connected togeather to get a positive/negative voltage of 18v to power the LM741?

Will 18v be ok ?

741's are supposed to be good to run on +/- 22V or up to 44V total between the V+ and V- power pins, however you split the supplies.

So using two 9V batteries for each of V+ and V- is fine.  This allows for higher amplitude signals through the op-amp, up to about 30V P-P at output.
Also OK to use two 9V batteries to get +/- 9V and this allows signals of about 14V P-P.

[Zero999]

Can I use 2 x 9v battery’s connected togeather to get a positive/negative voltage of 18v to power the LM741?

Will 18v be ok ?

Yes.

[rstofer]

Do understand that the voltage swing might be as low as +-10V given +-15V supply.  In other words, depending on the load, the OA can only get to 5V from the rails.  So, you might have a situation where your output swing can only be +-4V.

See "Output Voltage Swing" on page 5
http://www.ti.com/lit/ds/symlink/lm741.pdf

w2aew did a great video on op amps and what happens when the signal gets to the limit of swing:


Around 9:00, he shows on a scope how the output clamps.

The "Input Voltage Range" (also on page 5) is also limited to 3V away from the rails so +-6V if you are using a pair of 9V batteries.

[alsetalokin4017]

Note that R2 and R1 in these schematics form a voltage divider for the inverting input to the op-amp. It is fun to substitute other "Voltage dividers" for these two resistors -- like a potentiometer, with the wiper going to the inverting input, or a pair of Light-Dependent Resistors instead of the fixed resistors.

Also there are a bunch of op amps that have the same pinout. It is fun to set up a circuit on the breadboard and then pop in different opamps, or even same part number parts from different manufacturers, and see how differently they behave.

[Gazmon]

Can I use 2 x 9v battery’s connected togeather to get a positive/negative voltage of 18v to power the LM741?

Will 18v be ok ?

Yes.

I need to take the battery ground connection to the ground connection (0v) on my breadboard setup yes

[rstofer]

Yes, ground is as you shown it.  Now, connect the signal generator ground to this point.

Use the voltage follower circuit you provided in Reply 3 with, say, 10k resistors.  Keep the gain to 1 until round two of your experiments.

Keep your signal generator output low at about 1V peak to peak until round two.  I would put a 10k resistor in series with the signal to protect the op amp.  If my generator didn't swing around 0V I might have to put a capacitor in series with the signal.  Anything around 1 ufd up to 100 ufd will probably work at audio frequencies.

Remember, you can't get within 5V of the rails so your maximum signal swing is +-4V.  It's also worth noting, your batteries are a little low as the minimum supply voltage is +-10V for all variants.

Here is the datasheet:
http://www.ti.com/lit/ds/symlink/lm741.pdf

Every number is important.   Note that there are 3 devices:  LM741, LM741A and LM741C and they have different capabilities in terms of output voltage swing.  Your device should be marked but if it isn't, I would take the worst case of the 3 devices.

At some point, you may want to build up a dual 15V power supply.  I didn't need it but I just built:
https://www.jameco.com/z/JE215-Dual-Output-Adjustable-Linear-Regulated-Power-Supply-Kit_20626.html

[Gazmon]

Hi

I have attached my scope reading as they appear with my sigen input, why is my amplitude not correct to my outputted sigen signal

Just outputting a triangle waveform and cycling through the others

I’m connected as an non inverting I think , positive sigen connected to the -