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finding suitable op amp on ebay

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xReM1x

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hi! I got this schematic:
b8bb7f917b05e5b81ec177259c9de967.png

now, I cant find LT1638 cheap or suitable, and I need an op amp with supply range up to 30V and low voltage inputs.
the voltage divider that goes to the non-inverting input is going to be 30uV - 30mV. I dont know much about op amps so I dont really know how to serach for a suitable op amp, thats why I'm using ltspice opamps to test but there is not much op amps in LTSPICE that are sold on ebay.
 

KlausST

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Hi,

Look for:
* needed supply voltage range
* unity gain stability
* common mode input range includes gnd
* low offset voltage

Klaus
 

Audioguru

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Why buy a reject or a fake from ebay? Buy a REAL opamp from a genuine dealer for the manufacturer and electronic parts distributor.
 

xReM1x

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Why buy a reject or a fake from ebay? Buy a REAL opamp from a genuine dealer for the manufacturer and electronic parts distributor.
shipping for me cost 8$ most of the times. thats more than the cost of the parts I need. ebay for me is the cheapest.
 

Audioguru

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Why are you so cheap? Good quality parts do not cost much and the shipping of them is worth it.
A couple of days ago I spent $5.00 for gasoline to drive to one of the remaining electronic parts distributors in my city to buy four 1N5817 Schottky diodes. I am glad I did.
 

xReM1x

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Why are you so cheap? Good quality parts do not cost much and the shipping of them is worth it.
A couple of days ago I spent $5.00 for gasoline to drive to one of the remaining electronic parts distributors in my city to buy four 1N5817 Schottky diodes. I am glad I did.
well maybe because I'm 14. I dont have my own job (some sort, I still get money off doing somethings) and there is no LT1638 is any electronic store that isnt 2.5hours drive.
so, my only way is ordering. a single LT1638 cost 12shekels -> 3$. shipping - 8$. thats 11$ total for a 1cm silicon. thats why I'm looking on ebay -> everything for cheap free shipping.
I have more than 11$ that I can spend so if there is no any other options than I'm going to order it but the cheaper the better.
 

Audioguru

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and that was 12 years ago?
I still have the slide rule I used in school. It calculates that I was 14 years old exactly 55 years ago.
12 years ago I was preparing to receive an old age pension from my government since I was already retired. I received the pension for doing nothing for 9 years now and I keep receiving it.
 

BradtheRad

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An op amp is the preferred device in your schematic, because it is versatile and convenient to use. However there is a chance you can duplicate the function of the op amp, with the use of discrete components. It will require a lot of experimenting.

The op amp has a differential amplifier at the input. A long-tail pair is customary for this role. A current mirror may be involved too.

Then a half-bridge at the output. You may be able to get by with a transistor and pull-up resistor.
 

schmitt trigger

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Your schematic is nothing more than a ground-referred constant current sink.

The ubiquitous and cheap LM358 can work in your application, if you are willing to change ONE SPECIFICATION: namely the voltage range you require to amplify.
If instead of requiring 30 uV to 30 mV, you make it like 100 times larger from 3 mV to 3 V, you can make it work with the LM358A.

Of course the sense resistor will dissipate much more power, and the voltage compliance will be slightly above 3V.
 

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