Electronics > Beginners

Fake TL071?

(1/4) > >>

Ron Werner:
I needed a simple preamplifier, and found a schematic with a LF351, but not having that type in stock, I decided to use a TL071 instead. I have plenty of them (I thought) and they are supposedly to be an allround OK type of opamp.

Curious as I am, I decided to use my scope to check the result, using a (somewhat poor) 20 KHz square wave from my XR2207 generator.

The result was shocking, the TL071 didn't produce a square wave, but a triangular wave!

So, I tested a few other opamps (not all of them presented at the picture), and the general message is clear: there must be something awfully wrong with my TL071's!

Not all opamps did well, like the CA3140, but close enough probably.

The TL061 bought from a German dealer as far as I recall, did much better than the TL071 I bought from Ebay.

My NE5534's from several different sources did well (not on the picture), and gave a result close to that of my OPA134's, all of which gave identical results, as seen on the picture.

I read a thread here on the forum "Topic: What's inside the cheapest and fakest jellybean opamps", and the message was clear, there are a lot of fakes around.

What I wonder, this TL071, what is the issue here? Is it a completely disfunctional opamp, or is it some ultra-cheap opamp relabelled as the TL071?

Should I discard the whole lot, or is there some other use for them?

I included a picture of my circuit and the schematic, just to make sure that any error originating from a faulty design is seen directly.

Kleinstein:
Many fake OP-amps from china are some kind of LM358 versions.  A slew rate of some 0.2 V/µs sound about right to even a bit on the slow side.

magic:

--- Quote from: Ron Werner on June 19, 2022, 08:44:38 pm ---The result was shocking, the TL071 didn't produce a square wave, but a triangular wave!
--- End quote ---
All of them produce a trapezoid waveform - the transitions are not instant due to limited slew rate. The fake one is just the slowest of the bunch. If you decrease frequency or amplitude, its output will look "more square". If you increase frequency or amplitude, the others will become visibly distorted too.

Slew rate is exactly 6V/20µs, or 0.3V/µs, as you would expect from LM358. Conclusion: most likely another relabaled LM358.
If you test it with a DMM, you will find no continuity/resistance/diode/anything between the offset adjustment pins and ground, although there should be some.

Doctorandus_P:
China is especially keen on recycling, and they have got an entire town dedicated to recycling electronics.
The town is called "Giyju". Just type it in a search engine on internet, and you find pictures like below.

On either Ali or Ebay I also found pictures of the irlr8743. The good news here is that they are not pretending to sell these as new.

And why bother trying to buy stuff like this from shady sites? LF351 costs 35ct, or 28ct if you buy 25 of them.
https://www.tme.eu/nl/details/lf351d-st/smd-operationele-versterkers/stmicroelectronics/lf351d/
(Also checked LCSC, they cost 42ct (34ct 10+) over there. LCSC is mosty low-cost for stuff made in China, but not for imported stuff. Importing stuff into China is apparently very expensive too.

janoc:
Get a cheap LM358 and put it in your pre-amp. I am willing to bet you will have a pretty much identical result  :-DD

TL071, NE553x and anything that could be classed as "audio" or "audiophile" (as in being common in audio gear not because they are so great) on eBay (and also AliX, etc.) is pretty much 100% fake and those chips are relabeled jellybean cheapies - often some LM358 copies. Same thing with power transistors, electrolytic capacitors, etc. One would have thought that this common knowledge already, these issues are being reported for years and it is only getting worse with the semiconductor shortages (but these jellybean opamps are not exactly in short supply).

Don't buy semiconductors on eBay, it is as simple as that. Or if you do, then buy explicitly the Chinese made ICs - there you will at least have a reasonable chance that what you get actually matches what is in the datasheet.

Navigation

[0] Message Index

[#] Next page