Question about Op Amps

[Pat Amaral]

I'm a bit fuzzy when it comes to op amps and their use. Is there a reason why a 741 cannot be used in place of a 1458? If so, what are the particulars?

Thanks in advance,

[Disillusionist]

Hey Pat, If my memory still works, a 1458 is pretty much the equivalent of 2 741 op amps in one package. So I'm guessing they would be pretty much interchangeable except for the obvious differences in pin-outs and package size.

[tetsujin]

I'm a bit fuzzy when it comes to op amps and their use.

Basically, it works like this:

The op-amp has two inputs, + and -. The voltage on those two inputs is compared: if + is higher, then the voltage at the op-amp's output terminal increases, if - is higher, then the voltage at the op-amp's output terminal decreases. This change in the output happens pretty quickly, and it continues for as long as the voltage difference exists, or until the output voltage reaches the limitations of the device and its power supply.

A typical use of an op-amp is to use a voltage divider (that is, two resistors) to connect the negative terminal to ground and also to the op-amp's output. In this way, when the value on the positive terminal rises, the output will rise, causing the negative input to rise, too. The circuit can reach equilibrium this way, if the output rises enough to make the voltage at the negative terminal equal to that on the positive terminal. The output is then basically an amplified version of the input signal on the positive terminal. You can control the amplification by adjusting the values of the resistors in your voltage divider.

[jwrjr]

Disillusionist is, by the way, correct. A 1458 is, essentially, a dual 741 (do they still make those?)

[Pat Amaral]

Great info. Thanks to both of you. I happen to have a about a dozen 741s in my inventory but no 1458s. A few months ago, Virtualight posted a schematic for a photorp lighting effect (sorry I can't find it now - I thought it was on her site but, alas, it's proven elusive). I've been thinking of breadbording the circuit.

Thanks again,