Author Topic: TL081 weird glitch  (Read 1443 times)

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Offline magic

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Re: TL081 weird glitch
« Reply #25 on: November 15, 2019, 08:02:46 am »
We're not certain what it is but I tested it with the 1k resistor from 0 to 20kHz, I did not see the crossover distortion appear again at any of those frequencies. I can't comment on noise as I haven't done any real testing but just by looking at it, compares fairly well to the real TL081 I have, which is why I was so dumbfounded  ;D
Try 20kHz with enough gain for ±10V output swing and you will see other wonders of LM358.
And noise is not something you can measure on a scope unless it's really bad.

If it came from eBay, Ali or other unofficial source, assume it is counterfeit.  Or salvaged.  Doesn't matter what.
Salvaged can at least be useful when it comes to obsolete components, sometimes. But you better test it ;)

In an other thread about fake OPs they did die photos, showing something similar to LM358 - probably a Chinese version. The performance was more like slightly better than expected for a real 358. Given that the OPs are not that expensive - they could as well sold the chips as what they are. There definitely would be a market for a cheap improved 358.
I'm pretty sure you can buy legit Chinese jellybeans, just not on AliBay unless you know what you are doing.
If you are bored you could order one of each sort of LM358 from LCSC (there is a dozen) and see if they are any good.
Heck, maybe you will even find this one. The topology looks more or less the same as TI version and die dimensions are similar so I presume it was originally designed as a legit LM358 rather than solely for the sake of faking TL072s and OP07s. For starters, you wouldn't bother with input swing to ground if you were doing the latter.
 

Offline exe

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Re: TL081 weird glitch
« Reply #26 on: November 15, 2019, 09:58:12 am »
The designers of that opamp forgot to layout the resistor on the die.

It's a low-power opamp with 0.3mA supply current.
 

Offline imo

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Re: TL081 weird glitch
« Reply #27 on: November 15, 2019, 04:52:06 pm »
The designers of that opamp forgot to layout the resistor on the die.

It's a low-power opamp with 0.3mA supply current.

Try to wire a few kohm resistor from opamp's output against Vcc. It could be the glitch disappears..
Just tried, no luck, same thing. How could this help exactly ?
The designers of that opamp forgot to layout the resistor on the die. Next time you should order that opamp together with option #1 - "1k resistor for crossover distortion elimination"..  :-DD
 

Offline T3sl4co1l

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Re: TL081 weird glitch
« Reply #28 on: November 15, 2019, 05:18:14 pm »
That said, if you go for something like NE5532 you're basically using the same thing but with a class-AB biased output stage.  Very power hungry, but at least it doesn't have crossover distortion.

Tim
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Bringing a project to life?  Send me a message!
 

Offline magic

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Re: TL081 weird glitch
« Reply #29 on: November 15, 2019, 09:06:11 pm »
NE5532 is the secret LM358 option #1 with 1k pullup. The cat is out of the bag now. ;D

But seriously, what the hell is going on in this thread at this point?
« Last Edit: November 15, 2019, 09:07:44 pm by magic »
 
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Offline MagicSmoker

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Re: TL081 weird glitch
« Reply #30 on: November 16, 2019, 12:26:28 pm »
I don't get it because a TL081 only costs about 50 cents at Mouser electronics in quantity 1 and  you know you are getting the real thing, from TI.  Or if you wanty to go the discount route and don't mind to wait and wait, get them from Futurlec for 30 cents each.  What is one minute of your time worth, that got wasted debugging bad chips?  It's worth a lot more than 50c.  I would not warm up my scope for fifty cents.

This is the beginner section, so one should expect that a lot of the people starting threads here will not realize that counterfeits of even <$0.01 components can be found on fleabay, Ali-whatever, etc.

At least the OP learned this valuable lesson on a jellybean op-amp rather than, say, a $200 IGBT module...

 
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