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Offline hesammTopic starter
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« on: August 09, 2018, 04:05:52 am »
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it seems the LF357 is obsolete and can not be found easily, except fake ones. it is a good op-amp but it is not under production it seems.

I'm looking for a new substitute to introduce similar or better characteristics. Does anybody successfully tested any new part number as a replacement?

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Offline GoldDigger1950
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« Reply #1 on: August 09, 2018, 04:11:08 am »
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Companies often license thier parts to other manufacturers after obsolescence. Those so called fakes are just aftermarket parts. Have you tried them or have you simply relied on the rumors about them?

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« Reply #2 on: August 09, 2018, 04:33:04 am »
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Quote:Posted by GoldDigger1950
Companies often license thier parts to other manufacturers after obsolescence. Those so called fakes are just aftermarket parts. Have you tried them or have you simply relied on the rumors about them?


No Man. of course I tried many of them and none works as original. Besides, this component does not exist in any legitimate online store such as Digikey, Mouser and Farnell. It proves that it is not under production anymore nowhere (because it is old maybe) and the Chinese ones are other re-badged opamps such as 741

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« Reply #3 on: August 09, 2018, 06:02:39 am »
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Nope. I don't believe you have tried them. Had you done so, the aftermarket parts would have worked. I know. I tried many of them.

The F simply means JFET, low power. There is nothing else special about that part. A 741 will work but if you really want low power, try a TL031 in an 8 pin DIP package. That will work. I have tried that one and it is a drop in replacement.

The reason for low power is because of our use of batteries. The frequencies at which we operate make almost any op amp usable. Don't try to snow us here, mate. I've been an electronics engineer for decades and decades. I design metal detectors.

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« Reply #4 on: August 09, 2018, 06:31:56 am »
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Quote:Posted by GoldDigger1950
Nope. I don't believe you have tried them. Had you done so, the aftermarket parts would have worked. I know. I tried many of them.

The F simply means JFET, low power. There is nothing else special about that part. A 741 will work but if you really want low power, try a TL031 in an 8 pin DIP package. That will work. I have tried that one and it is a drop in replacement.

The reason for low power is because of our use of batteries. The frequencies at which we operate make almost any op amp usable. Don't try to snow us here, mate. I've been an electronics engineer for decades and decades. I design metal detectors.


Please leave me alone if you don't believe. I believe you have not ever designed something because you don't know the difference between opamps. if you have not faced some fake parts, it does not mean they don't exist. I am not bounded to use obsolete parts. Please don't reply to my comments I don't need your help.

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« Last Edit: August 09, 2018, 06:34:50 am by hesamm »
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Offline GoldDigger1950
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« Reply #5 on: August 09, 2018, 06:51:15 am »
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Quote:Posted by hesamm
Please leave me alone if you don't believe. I believe you have not ever designed something because you don't know the difference between opamps. if you have not faced some fake parts, it does not mean they don't exist. I am not bounded to use obsolete parts. Please don't reply to my comments I don't need your help.

You asked for help, and I am offering it. I hold several patents for metal detector circuits. I am also a career electronics engineer. When you come here asking for help and then tell us you tried things that would have worked then you are either using bad parts or you haven't actually tried them, as you claim.

I have thousands of spare parts in my engineering lab and may actually have a few of the parts you need. Getting snarky with me won't encourage me to offer you one, as I have done with hundreds of other members. I often send spare parts to members here. You just went way down on my list.

I will no longer trouble you with facts. Instead, rely on those who don't really know. All your choice. Oh, and do remember that I am a moderator here. For a good reason.

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« Reply #6 on: August 09, 2018, 07:32:57 pm »
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 You ask a Question.  You got the answer.  Be Happy.

If you look around the LM357 is still around.   I can buy them here in town.  Hell I have a few in stock.  

If you do your homework there are a pile of other op amps that are a fraction the price and way much better is specs.

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https://www.utsource.net/itm/p/248353.html?adgroupid=44391740863&keyword=lf357&adposition=1t1&gclid=Cj0KCQjwzK_bBRDDARIsAFQF7zPxXCt0mhIKtxoDIeNmm8VtFQ_J4BOOabrAhPyzaid1Uj5xHWok7dEaArX2EALw_wcB



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https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR11.TRC1.A0.H0.XLF357.TRS0&_nkw=LF357&_sacat=0



I would go with GD's suggestion .  The man knows what he's talking about.  

You have plenty of options.  It's just a JFET Op AMP.  


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« Last Edit: August 09, 2018, 07:59:21 pm by Homefire »
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Offline GoldDigger1950
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« Reply #7 on: August 10, 2018, 03:13:38 am »
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Also, Homefire, the main reason for using the JFET op amp is to save power. We operate at audio and ultrasonic frequencies so just about any old op amp with the same pinout will function. The power consumption of a single op amp won't necessarily make that much difference all by itself but combine it with other circuit components and the low power contribution to the circuit is handy.

As I said earlier, had he actually tried other op amps, he would have seen that they work just fine but consume a little more power. I believe he was making his post sound more dramatic by saying he tried others. He should learn that help here is real, it is fast and it is normally accurate. We have no need to deceive anyone.

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« Reply #8 on: August 10, 2018, 09:10:40 am »
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  I guess he's locked in the  mind set the OP Amp is giving him issues when in fact there may be other issues with his circuit ?      :Smiley

Yep.  For most of our applications we have plenty of op amp options.  In most cases if the pin out and power requirements are the same they will at least function well enough to get things working.  

I buy chines bits and bobs all the  time.   To this day have never found a obviously fake component.   More then a few have been right on the line with Tolerances and or Specs but still within.    I have some Zener's here that came marked as one value but turned out to be another.    Just wrote it off as ""CHIT HAPPENS""  I couldn't afford to do all the stuff I do paying State Side prices for all the stuff I buy.  

My current Bench Stock is better then our old Radio Shack had to offer.  LOL  

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« Last Edit: August 10, 2018, 09:12:14 am by Homefire »
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« Reply #9 on: August 10, 2018, 09:49:26 am »
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I have tons of spare parts I have gathered over the past 50 years. When I need an op amp or other part, I generally buy 10 or 20, as cheap as they are. Comes in handy.

When Xavier was building a detector, I sent him almost a full pound of parts which included every part he needed for the project. He nearly had a "tech-gasm" over the package when it arrived.

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