Electronics > Beginners

TL081 weird glitch

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sheisthedarkness:
Hello, I bought a bunch of TL081CP from eBay and I got a different revision from the ones I already have. Making a simple negative gain circuit with any of the 15 I bought causes these glitches in both the input and output signal as pictured in the attachment. The exact same circuit with only the opamp swapped out for one of the older ones I have does not exhibit this problem, signal is clear as it should be. When the opamps are powered off the signal also gets  through perfectly.  The older revision has the code "86AEP2M" while the new ones have "18MDSCH". At first I thought they were low quality chinese parts but I found it weird that they'd all exhibit the same imperfection.
Does anybody have a clue as to what might cause this or what could be done to correct the problem ? Thank you in advance.

magic:

--- Quote from: sheisthedarkness on November 14, 2019, 04:29:40 pm ---weird glitch
--- End quote ---

--- Quote from: sheisthedarkness on November 14, 2019, 04:29:40 pm ---eBay
--- End quote ---

Another one :-DD

https://www.eevblog.com/forum/beginners/opamp-input-offsets-working-in-the-opposite-direction-to-what-i-expect/

And yeah, welcome to the forum, I guess. We have those threads every other month now :)
Maybe eBay should pay Dave to put up a banner ad informing that opamps from auction sites are fake :-+

wraper:
You got not TL081 but something completely different. There is little chance getting genuine op amps on ebay, even piss-poor LM358. Especially when price is on lower side.

sheisthedarkness:

--- Quote from: wraper on November 14, 2019, 04:34:53 pm ---You got not TL081 but something completely different. There is little chance getting genuine op amps on ebay, even piss-poor LM358. Especially when price is on lower side.

--- End quote ---
Oh, well that's unfortunate. I didn't think something like that would be worth faking. How bad is it that it can't reliably give me a gain of 2 at 1kHz ? Or am I using whatever it is wrong by using it like I would a TL081 ?


--- Quote from: magic on November 14, 2019, 04:34:19 pm ---And yeah, welcome to the forum, I guess. We have those threads every other month now :)

--- End quote ---
Thanks, I searched "TL081" but couldn't find anything relevant so I made the thread. The link you sent is surprisingly similar lol.

magic:
It apparently is worth faking ::)
Somebody just buys those LM358/LM324 dies and has them packaged as single, dual or quad and prints whatever markings that are in demand given week on top.

Gain of 2 at 1kHz shouldn't be a problem for LM358. But do you have a problem with gain or is your only complaint the distortion near zero crossing? The distortion is crossover distortion, it's kinda expected in this opamp regardless of gain.

Not sure what to think about the input side glitches. Perhaps it's capacitive coupling from the output (what's the source impedance driving the amplifier) or perhaps it is somehow caused by input stage overload when the output stage is switching polarity and completely unresponsive. Try some legit LM358 from a reputable manufacturer if you have one.

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