Why? The opamp is superfluous anyway. It serves no purpose.

Why do you think you need it?

Hint: If your signal generator could only output 1mA, you would need a buffer.

So you recon it will work without the op amp anyway? Would it work with the op amp buffer,

 

Let us put it this way.

This equation represents Ohm's Law:

I = V / R

There are three variables, I, V, and R.

If two variables are known, then the third variable is determinate. It cannot have some arbitrary value.
If I and V are fixed, then R must be fixed.

If V and R are fixed, then I is fixed as well.

 

So the maximum current that can be input is 20uF?

No. That's the total current in differential amplifier.Trying to have 20uA in one input would cause the opamp to not function.

 

Why? The opamp is superfluous anyway. It serves no purpose.

Why do you think you need it?

Hint: If your signal generator could only output 1mA, you would need a buffer.

The impedance of my signal generator can be adjusted from 5 ohms to 650 ohms as it states of the data sheet what would you set it to for the best matching

 

Would 1

No. That's the total current in differential amplifier.Trying to have 20uA in one input would cause the opamp to not function.

Would 1uA be too large

 

No. That's the total current in differential amplifier.Trying to have 20uA in one input would cause the opamp to not function.

Perfect, this is all I needed to know. Thanks so much.

 

Would 1
Would 1uA be too large

I'd go higher; 2-3uA.

Have you even bothered to look at the datasheet?

You want the input voltages to be at least an order of magnitude greater than 7.5mV (worst case input offset voltage). You want the input current to be at least an order of magnitude greater than 0.2uA (worst case input offset current).

 

I'd go higher; 2-3uA.

Have you even bothered to look at the datasheet?
View attachment 331008
You want the input voltages to be at least an order of magnitude greater than 7.5mV (worst case input offset voltage). You want the input current to be at least an order of magnitude greater than 0.2uA (worst case input offset current).

Yes I looked, I just don't know how to interpret it very well. Could you help please?

Is this the current that I would need at the non inverting pin?

If I input a 2V signal into the LM741 would it work correctly?

 

The input resistance of the LM741 is 2 MΩ.

If you apply 2 V on the input, Ohm's Law gives the current.

I = V / R

I = 2 V / 2 MΩ = 1 μA

Too high or too low is irrelevant. You don't have a say in the matter.

 

The input resistance of the LM741 is 2 MΩ.

If you apply 2 V on the input, Ohm's Law gives the current.

I = V / R

I = 2 V / 2 MΩ = 1 μA

Too high or too low is irrelevant. You don't have a say in the matter.

Yes I worked out this value, again thanks for the help with this . All I would like to know is would I be able to use the op amp to buffer the 2V signal from the signal generator please

 

What's all this 741 load stuff by Bob Pease, Santa Clara
Effect of Heavy Loads on Accuracy & Linearity of Op Amp Circuits (Rev. B) (ti.com)
A nice triangle wave input and for output if there is distortion reduce the gain and it has 10mA for this test.

Absolute Maximum that the LM741 will dissipate is 500mW by American standards,
when it's that hot the output suffers it is rough, not shown, and would not pass most quality assurance departments.

And not every application needs an undistorted wave, accuracy or linearity.
Max Supply +/- 22Vdc, the Nominal supply +/-15V* is the industry standard supply voltage. However +/-22Vdc can be used.
See note *
(5) For supply voltages less than ±15 V, the absolute maximum input voltage is equal to the supply voltage.
LM741 data sheet, product information and support | TI.com

 

Yes I worked out this value, again thanks for the help with this . All I would like to know is would I be able to use the op amp to buffer the 2V signal from the signal generator please

That I cannot answer. What do you mean by buffer?
The signal generator is good to 20 mA, i.e. a 200 Ω load.
Can the LM741 do any better? I don't think so.

 

That I cannot answer. What do you mean by buffer?
The signal generator is good to 20 mA, i.e. a 200 Ω load.
Can the LM741 do any better? I don't think so.

Sorry I think I have miscommunication. English is not my first language. Please see the datasheet. I worked out my input bias to be 1uA. Am I correct in saying the op amp will work correctly because it is within this range?

I intend to apply the 2V signal, to a LM741 buffer and then to my other circuit.

 

There is no improvement to using the LM741 op amp.
Why not just connect the output of the signal generator to your "other circuit"?

 

So you recon it will work without the op amp anyway? Would it work with the op amp buffer,

It depends. A 741 will distort a sine wave above 9KHz.

You still have not told us:

1. why you think you need to use a buffer

2. why you think you need to match the impedance

3. why you think a buffer would do that

All of three of those assumptions are wrong. So, if you want to learn something, try to understand why they are wrong.

You need to understand basic DC circuits before you can even start with AC circuits like filters.

 

It depends. A 741 will distort a sine wave above 9KHz.

You still have not told us:

1. why you think you need to use a buffer

2. why you think you need to match the impedance

3. why you think a buffer would do that

All of three of those assumptions are wrong. So, if you want to learn something, try to understand why they are wrong.

You need to understand basic DC circuits before you can even start with AC circuits like filters.

Hello,

I think I will need a buffer circuit to impedance match the filter to the signal generator which has an impedance of between 5-640Hz (This can be adjusted)

As the frequency varies due to the RLC band stop filter this will change the impedance of the circuit. This is why I think I require the buffer amplifier.

A buffer amplifier has a high impedance input and a low impedance output. This will ensure that the signal isolated from the effects of loading between circuit stages

Would this be incorrect?

 

There is no improvement to using the LM741 op amp.
Why not just connect the output of the signal generator to your "other circuit"?

Am I correct in saying that the buffer amplifier will work though because it within the maximum of1.5uA as stated on the datasheet.

 

The Rhodes & Schwartz signal generator is designed to drive 50 Ω loads while the LM741 is not.

 

The Rhodes & Schwartz signal generator is designed to drive 50 Ω loads while the LM741 is not.

By my RLC band stop filter is not 50 Ohms? The impedance will vary with the frequency of the signal applied to the circuit

 

By my RLC band stop filter is not 50 Ohms? The impedance will vary with the frequency of the signal applied to the circuit

Correct, but never less than 300 Ohms.