Fake TL071? - Page 1
Forum section: electronics / beginners

author: Ron Werner
author_rank: Contributor
timestamp: June 19, 2022, 08:44:38 pm
content: 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 19, 2022, 08:51:12 pm
content: 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.

author: magic
author_rank: Super Contributor
timestamp: June 19, 2022, 09:05:29 pm
content: Quote from: Ron Werner on June 19, 2022, 08:44:38 pmAll 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.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 19, 2022, 09:09:59 pm
content: 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.

author: janoc
author_rank: Super Contributor
timestamp: June 19, 2022, 09:10:27 pm
content: Get a cheap LM358 and put it in your pre-amp. I am willing to bet you will have a pretty much identical resultTL071, 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.

author: dietert1
author_rank: Super Contributor
timestamp: June 19, 2022, 09:19:08 pm
content: As far as i understand your measurements are clipping. The schematics shows a noninverting 101x amplifier, so you can't drive that with 1 Vpp. What happens if you reduce the input signal in order to stay in the linear output region?If the "TL071" stays as bad, it's a bad part. You can't save by buying basic parts at ebay.There is a huge difference expected between a TL071 or the like and a OPA134.Regards, Dieter

author: Ron Werner
author_rank: Contributor
timestamp: June 19, 2022, 10:55:40 pm
content: Thanks, helpful replies!I went as low as I could with the input voltage, less than 30mV, noisy signal at the scope, but still recognizable as a square wave.At ca. 20KHz the TL071 still produced a sawtooth, while the OPA134 did well.I had to go down to ca. 3KHz with the "TL071" before the result was a still rounded but now recognizable square.I measured the 1/8 pins in relation to pin 4, and there is nothing whatsoever.All in all it confirms what you have been telling me, maybe some LM358 (or worse).No doubt I will be more choosy next time, but I have had a lot of good experiences on Ebay, and bought components that were so specific, that some relabelled component hadn't been working at all.Like the AD8303 I used recently for some detector experiments. I had a certified good one, and the much cheaper Ebayers matched the results.But my oh my, must they be desperate to pick all that old electronics apart just to make a few bucks. There must be more pleasant ways to earn a living. I guess they expose themselves to a lot of poisenous stuff.I didn't know TME, but I will see what they have for me. I bought some components from Mouser in the days I had more money to spend, but throwing it away on garbage is not helping my wallet either.

author: ledtester
author_rank: Super Contributor
timestamp: June 19, 2022, 11:57:21 pm
content: I got lucky with some TL082's from ebay but also got fake TL072's:https://www.eevblog.com/forum/beginners/op-amp-square-waves/msg922779/#msg922779In particular, the TL072's I got from ebay produced really strange waveforms when plugged into the classic oscillator circuit (shown in the above thread).

author: MikeK
author_rank: Super Contributor
timestamp: June 20, 2022, 12:33:45 am
content: They're even selling fake 741's!

author: magic
author_rank: Super Contributor
timestamp: June 20, 2022, 06:03:58 am
content: EBay is OK if you only buy from European vendors who have been long in the business and are selling their old stock. Most of them used to supply electronics repair shops in the past and you can recognize them by their stores being full of specialized ICs for audio, TV, CRT displays, etc.If a store mostly sells Arduino stuff and maybe a few very basic analog parts like NE555, LM358, LM386, TL072, NE5532 then it's a new store targeting hobbyists and there is a risk it's importing components from bottom of the barrel Chinese suppliers. Some of them may be buying from legitimate vendors, their prices will be higher.If a store sells ICs for electronics hobbyists or audiophools directly from China, run and don't look back

author: strawberry
author_rank: Super Contributor
timestamp: June 20, 2022, 06:49:25 am
content: used parts in general are not bad but factory rejects and relabeling is bad practice

author: janoc
author_rank: Super Contributor
timestamp: June 20, 2022, 07:14:45 am
content: Quote from: Ron Werner on June 19, 2022, 10:55:40 pmElectronic trash recycling is a big business - and when you are poor with no prospect of another way of making a living, you don't get to be picky about things like poisoning yourself or the environment. The only way to get rid of this is to stop living this disposable lifestyle where a computer or a phone gets thrown away every 2-3 years once the battery inevitably dies because they are economically unrepairable. And start to properly recycle our junk instead of the "recyclers" exporting and dumping it somewhere in Africa or Asia instead.However, it is not likely that the fake opamps you have got were relabeled pulls. More likely someone took a cheap jellybean Chinese-made opamp in the same package (most have the same standard pinout - how nice!) and relabeled it as something more expensive/desirable.Pulls happen too but mostly for rare/out of production components - e.g. I have got 5 AY-3-8910 sound generators like that, which are clearly pulls. Also some GAL16V8s from AliExpress. However, in those cases it was clearly indicated by the seller that the chips are "recycled" and not sold as new, so no problem.I doubt someone would refurbish a few cents worth of desoldered opamps to sell as new. But then I did get some "recycled" and relabeled EEPROMs too (including the data of the original owner!), so who knows.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: June 20, 2022, 03:42:56 pm
content: I would try it without the input and output capacitors and reduce the input amplitude.

author: Ron Werner
author_rank: Contributor
timestamp: June 23, 2022, 10:24:15 pm
content: I just finish making a more functional setup for testing opamps, with a square wave generator TS555 and a wave form shaper with a CD40106, frequency from virtually 0 til ca. 500 KHz.I tested my fake TL071 at 8 KHz and 60 Khz and compared it with some other. I refer to the pictures. I think they say enough, and I threw away the remaining IC's, a pity, but it has learned me to be much more careful where to buy next time.I am not 100% sure, but as far as I recall I bought this NE5534 also on Ebay, the TL081 probably from Segor Electronics in Germany. The TL071 sop8 most certainly from Ebay.Anyway, if there are any naive newbies left, I hope they now appreciate how important it is to get yourself some proper equipment. I most certainly do!PS green signal is from the wave generator but NOT shaped, the signal comes directly from the TS555!

author: magic
author_rank: Super Contributor
timestamp: June 23, 2022, 10:43:14 pm
content: Definitely fake.Something vaguely resembling the TI logo but different package shape than TI.It looks exactly like standard AliBay junk.

author: janoc
author_rank: Super Contributor
timestamp: June 24, 2022, 08:21:41 pm
content: I would try to wipe the marking off with some acetone. Sometimes it can be rather enlightening what gets revealed under the fake label.

author: Gyro
author_rank: Super Contributor
timestamp: June 24, 2022, 08:38:13 pm
content: That molding flash is so rough that I doubt there is any original marking to be revealed. With parts like that they just fresh package any old crap die.

author: magic
author_rank: Super Contributor
timestamp: June 24, 2022, 10:45:30 pm
content: The markings are laser etched and there is no trace of sanding (except in rare cases).The dice inside are LM358 or RC4558 clones from unknown Chinese manufacturers.The trick where one half of LM358 is connected in standard single channel pinout (with offset pins floating) must be a custom order from the packaging house - you won't find such chips anywhere else.It's not hard to imagine how they come into existence and achieve the form that we buy.This process must be cheaper than remarking recycled ICs, because most junk on auction sites is like that.