Hi, I need some help here, I want to calculate the maximum operating frequency that will not cause distortion in my output signal due to slew rate characteristics, for the ampop lm741, for example if I have 1 Volt amplitude in my input and I have a gain af=20dB (linear 10) and another case if I have a gain af=60 dB (linear 1000)?

From the datasheet, the slew rate for the Lm741 is about 0.5V/us, but how can I find the maximum frequency? Is there a formula to calculate it? Thanks, I hope you understand my doubts.

 

The slew rate of a sinewave is (2π * Vp * f) where Vp is the peak voltage (not peak to peak or RMS) and f is the frequency.

Note that the slew-rate is for the output amplitude and is not significantly affected by the circuit gain.

And obviously with a gain of 1000, the output will be well saturated with a 1V input and the slew rate is of little concern.

 

The 741 may work up to about 9 kHz but hoping for low distortion may be a bridge too far.

 

The noisy 741 opamp is 54 years old and was never designed to play good music. It might have been used in some muffled AM radios.

 

In the late 70's / early 80's we got two Sony 1" Type C videotape decks. These were their top professional products, intended to push 2" quad machines out of the market. Good (but not great) pictures, but surprisingly hissy audio. Turns out they were full of 741's. Shotgunned them with 5534's, instant 12 dB s/n improvement.

ak

 

Look at the gain-bandwidth product of any op-amp.
Typically, the gain-bandwidth product of LM741 is 1MHz. Thus at 1MHz, the gain is 1.



https://www.allaboutelectronics.org/gain-bandwidth-product-of-the-op-amp/

 

Slew Rate and Frequency Response are different specs. An LM741 opamp has a frequency response of 1MHz when its gain is 1 but its output cannot "slew" fast enough to produce waveforms over 9kHz.

Most opamp datasheets show a graph of "Maximum Peak Output voltage vs Frequency" but it is typical and some are better and some are worse.
Lousy old opamps like LM741 reach 9kHz and LM324 and LM358 reach only 5kHz.
Audio opamps like TL07x reach 100kHz and OPA2134 reaches 240kHz.

 

Not to defend the "lousy old op amps" but to clarify, the 9kHz or so maximum 741 frequency limit due to slew-rate is for an output of 10Vpk.
For an a max audio frequency of 20kHz the maximum peak signal would be abut 4Vpk (if not limited by the gain-bandwidth).

But its noise, of course, makes the 741 a lousy audio amp.

 

I like listening to music that has a wide dynamic range without much "compression". I do not want the loudest peaks distorted with slew-rate-limiting so I use audio opamps not lousy old opamps.

The lousy old opamps work fine when playing heavily-compressed and muffled AM radio sound.

 

The noisy 741 opamp is 54 years old and was never designed to play good music. It might have been used in some muffled AM radios.

Interesting to note that the NE5534 is now 43 years old!

 

The fairly old NE5534 cheats a little because it has decompensation causing it to be unstable with a gain less than 3 times.
The NE5532 is a stereo dual opamp that has proper compensation and has a little more noise than the NE5534.

Signetics also invented the NE555 timer 50 years ago and Signetics was bought by Philips 47 years ago.