Which one can replace the LM318 OP-AMP

Hello, everyone!
Recently, I found a peak hold circuit on the Internet, which uses lf355 and lm318. So I learn about its datasheet and go to buy it. But when I went to the electronics store to buy it, I was told that there was no such model. He said that this part is very rare. Very helpless.
So I would like to ask, is there any common integrated op-amp model that can replace these two chips?
Hope for some advice!
Thank you!

I think that circuit design is very old and you should look for a more recent design that uses currently available ICs and it will probably work better too.

At least it is equally popular in 10 random countries ???
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Buy your self a breadboard, and some 10 different cheap opamps in DIP format and start experimenting.

Also get with a few good books (or at least one) about Opamps, and their peculiarities, and combine that with real experiments to get a real feeling of the differences in opamp parameters, and which parameters are important in different applications.

The old LM741 is probably still widely used and very cheap. It’s probably the oldest (and worst) opamp that was good enough to still be used today. It is particularly worth experimenting with to examine it’s flaws and weaknesses in different applications.
(Edit: Oops. It’s really showing it’s age. It’s (finally?) getting obsolete and not available at all, or horribly expensive (I see EUR20 variants ???)

But for breadboard experiments… It really does not matter much. Get a few of the cheapest that are sold in DIP packages. Make sure you get a few with a BJT input stage and a few with a FET input stage. Think of a circuit (from theory) and then build it to verify the main difference between these two. Another important difference is “rail-to-rail” versus (around 2V) of headroom around both supply rails, or the good old (and certainly still very common) LM358 which inputs can be driven from (very slighly) below the negative voltage rails.

“Rail to Rail” is a very unfortunate marketing term. For some weird reason it has never become good practice to clearly state needed headroom for both input and output voltages margins on both supply rails.

“The art of Electronics” from Horowitz / Hill is a very good book, but somewhat expensive (EUR80 or so) but worth it’s price.

“Opamps for Everyone”, a.k.a. slod006b is a good opamp book from Ti, which was once printed on paper, (there are 2nd hand copies) but now it’s freely available as PDF.

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What country are you in? Even though we have a worldwide IC “Chip shortage” Digikey has many thousands of LM318’s.

https://www.digikey.com/en/products/filter/linear-amplifiers-instrumentation-op-amps-buffer-amps/687?s=N4IgTCBcDaIDIFkDMBGAHCAugXyA

It is a single source device originally from National Semiconductor > now Texas Instruments. But many newer ICs are single sourced. The LM318 has been around for…40 to 50 years? and I have been engineering for about 45 years. The LM318 may not be the best at anything any more, but I would not dissuade anyone from using it if there was any sort of good reason to do so.

I suspect that the LM318 was probably designed by Bob Widlar. He was a genius and a legend; if you can google some information about him it would be quite interesting.

https://www.edn.com/bob-widlar-cherry-bombs-the-intercom-speaker/

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Yes, the datasheet I was indicated it was released in the 1970’s!

Depending on what the circuit does, something as simple as the TL071 / 72 / 74 may do what you want, and be a lot cheaper! (the LM741 is 1970’s too)

Maybe you did not noticed, but today probably over 50% of chips are not easily available, and prohibitively expensive. Scary situation for us all depending on those gadgets.

Wow, you really estimate 50%?

Maybe I have bad luck with chips selection (ST, baby… ) but this estimation is based on my experience.
Of course, OMMV.
Anyway the situation is plain wrong. Lot of companied do rework their designs just to keep manufacturing their products.

I am aware of the shortages.
About a year ago prices for PC processors went up by approx 20% and those are just slightly affected.
Videocards from AMD are impossible to buy for a reasonable price. They still cost double or triple what they did before Covid and the latest currency mining thing happened, and it’s why I’ve decided to wait another year or so before I buy a new PC with a 4K monitor.
Only option at this moment would be a Ryzen 5600G for me, and that’s a pretty tempting idea…

But I had not connected the dots to consider the LM741 would be affected too. Chances are it’s being pushed out of the market now and will never come back.

I’ve got about 15 of them lying in some drawer for 30+ years. I used to desolder such part from scavenged electronics when I was young. Anybody want to buy some?

Just for fun I had a look at both Ebay and Ali. Ebay is all over the place, but Ali is often between 10ct and 20ct. I wonder what opamp can be faked into a LM741? Properties of a lot of the dual opamps are close to the LM358 on Ali, regardless of what is printed on the top.

[Edit]
Out of curiousity I had a look directly at Digikey’s database.
The’ve still got 20.000 on storage for 91ct each, and that is probably a “normal” price for Digikey. The crazy expensive versions are with metal can, or ceramic case.

The LM318 is noteworthy for having a fast output slew rate; many volts per microsecond. That is advantageous for a sample hold circuit which I understand to be the desired application. I remember that in my early days as an apps engineer at Exar, I was trying to build a peak detector. It was easy to see that op amp output slew rate was a limiting factor. These days there are other op amps which are as fast or faster, but the LM741 is slow; probably 0.5 volts per microsecond. Some of the JFET input types such as TL074 are probably faster and might work. But use care when substituting because this sounds like one application where “just any old op amp” might not work. I would assume that to be true for any good design which originally specified LM318.

Yes indeed.
The LM741 has gotten much more attention in this thread than this obsolete part deserves, and for a Sample & Hold circuit you do indeed want a fast opamp, and one that does not misbehave when it’s inputs are not at the same level.

I would not advise the LM741 for any real circuit, but because it is so slow and it’s flaws are big, they’re relatively easy to find and show on your oscilloscope, and therefore it’s a good part for educational purposes.

That’s a bit harsh.
I have a whole box full of them somewhere in my shed. Brand new (50years ago), never used, TO99 cased, must be worth a fortune.
All I need to do is find (con) the right museums into buying them!

Have a box of LM723s in TO100 packages also… another fortune!

And a couple of dozen 2N2646 UJTs in TO18s … any-one remember them.

And a pile of BRY39s in TO72s…Put, Put, Puts.

Absolutely amazing what accumulates over a lifetime: good job my shed is big and the other household boss (her) is forgiving! :slightly_smiling_face:

PS there are a few “valves” lurking somewhere also.

I had a similar need and ran into the same problems of parts availability and high costs of the LM318. Here is the circuit I currently use. An unamplified audio input goes into DACOUT (I use left channel audio). The output of the circuit is AUDIO_ADC which I feed into a microcontroller analog input pin and read the value.

They are easily available provided you can order what you want and wait till second half of 2023 to get your order :slight_smile:
I have heard that the reason is that Japan factory providing 30% of the world’s production of semiconductor wafers was burned (march 2021 I think).

We got into new procedure:

  1. We agree with contract manufacturer a list of elements and their footprints.
  2. He checks if those elements he will be able to get and for what date.
  3. If needed we change the list, and so on…
  4. He orders those elements (and tells me that he got confirmation).
  5. I redesign PCB to fit to agreed list.

Last few months I am doing only these.

For me it is 100% but I am looking only at microcontrollers, memorries, RS485 transivers, LDOs, DCDCs. I don’t know how with OpAms.

That is the current estimate :crazy_face: :tired_face: :japanese_ogre:

Plenty of complaints, also on EEVblog/forum. STM32 uC families are apparently particularly troublesome.

I suggest to read all pdf’s here:
https://www.analog.com/en/education/education-library/op-amp-applications-handbook.html
I didn’t checked what is inside but I just believe Analog Devices.

The STM package and test factory had a major COVID outbreak a month or so back. I guess production stopped

That looks incredibly like a “Precision Rectifier” circuit I used… In my case, I took in an audio signal, rectified it, then used a comparator to compare it a defined DC level (to give me some pulses out when audio of a suitably high level was present. In your case, you’re reading the actual DC voltage.

My circuit uses a TL074 quite successfully

(the 1nF’s are there to stop the damn thing oscillating!!)

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I’ve noticed some drift with my circuit in that the readings at first are very accurate and then lean towards higher and then lower levels. I’d had to add code to recalibrate between sound playback which is annoying. I wonder if 1nFs would help!