OPAMPS - Aliexpress vs the real thing, need an explanation

[cornleader]

I built a very basic opamp buffer circuit on perfboard and taped it to my guitar strap, it works great. I always socket my ICs so I can swap different ones in and out. I have some TL072s from digikey I bought many years ago and I have some of China's best .05 cent TL072s I picked up from aliexpress recently. To my ear they both seemed to work in my buffer. No way I said so I hooked up the scope and and cranked up the freq. I usually set my signal generator to a 400Mv sign wave at 440Hz. This time I set up a square wave about 2v and 23kHz. Here are my results. I am far from an electrical engineer but I know enough to make myself dangerous lol. I am asking the gurus here to explain what is happening in these images.

China


Digikey

[JTEX]

The China amp has much lower bandwidth than the real TL072, which shows on the scope as much longer rise/fall times with a higher frequency square wave. Needless to say, what's printed on the chip is not what's inside. You might also want to measure the chip's current draw and compare to spec.

You're taking a big gamble by buying chips from shady sources such as AliExpress or random eBay sellers. If you're going to buy from China, they do have legitimate distributors such as LCSC.

[cornleader]

I didn't expect much to begin with but they do "work" for some basic breadboard projects. I just checked my chips from Tayda and the slew rate seems ok. I use lots of 072s and 4558s. I was getting low on my legit chips so I tried one of my many 3 cent opamps and it worked... thats when I hooked up the scope.

[R.G.]

The circuit matters too. A buffer is generally a low- or even unity-gain circuit. For opamps, that's a high feedback circuit, and high feedback in general gives the best possible frequency response. It's when you get into circuits that need high gain (= less feedback) that you run out of gain to keep response fast.

Yeah, even cheapo counterfeit-re-labeled-knockoff stuff will sometimes work OK as a buffer.

[duck_arse]

I usually set my signal generator to a 400Mv sign wave at 440Hz.

don't do this. 400 Megavolts will fritz those china's best, fer sher.

also, welcome to the forum.

[cornleader]

I usually set my signal generator to a 400Mv sign wave at 440Hz.

don't do this. 400 Megavolts will fritz those china's best, fer sher.

also, welcome to the forum.

Thanks

400mV

better lol
...I did say I am far from an electrical engineer.

[cornleader]

The circuit matters too. A buffer is generally a low- or even unity-gain circuit. For opamps, that's a high feedback circuit, and high feedback in general gives the best possible frequency response. It's when you get into circuits that need high gain (= less feedback) that you run out of gain to keep response fast.

Yeah, even cheapo counterfeit-re-labeled-knockoff stuff will sometimes work OK as a buffer.

This is so true. My buffer is unity gain and I used fake 072s and 4558s against the real ones and no different in sound to my ears. Now... if I use the fake ones as gain stages forget it, the circuit is dead.

I bought a metric crap ton of components from aliexpress for next to nothing just to see. I just wanted to have cheap stuff to prototype on breadboards with. Resistors film caps and ceramic caps were ok for breadboards but the electrolytics are pure firecracker garbage. Funny how 100 different 3904 transistors from china all have exactly an hFE of 431. not 432 or even a 430. Every one measures exactly 431.

I never compared any of the cheap parts on the scope to check performance. Interesting to see what is going on.

[JTEX]

I usually set my signal generator to a 400Mv sign wave at 440Hz.

don't do this. 400 Megavolts will fritz those china's best, fer sher.

also, welcome to the forum.

He's correct, Mv = Mega vilts. 1 vilt = 1 picoVolt, so 400Mv = 400mV.
 

[cornleader]

He's correct, Mv = Mega vilts. 1 vilt = 1 picoVolt, so 400Mv = 400mV.
 

I did say from the begining "I am far from an electrical engineer but I know enough to make myself dangerous"

[Elektrojänis]

Funny how 100 different 3904 transistors from china all have exactly an hFE of 431. not 432 or even a 430. Every one measures exactly 431.

Isn't hFE of 431 a bit high for a 2n3904?

Anyway... First thing that came to mind from your slew rate graphs was that maybe those fake TL072 opamps would make good candidates for Proco Rat clones? (For people whom the slow slew rate matters in those.)

[cornleader]

Isn't hFE of 431 a bit high for a 2n3904?

Not for chinas best! I think my legit 3904 are around 260ish, they vary, all 100 fake 3904 test at exactly 431. I wasn't expecting them to be real when you can get 100 transistors for $1.50, that includes the shipping to Canada lol. But I had to see for myself!

Anyway... First thing that came to mind from your slew rate graphs was that maybe those fake TL072 opamps would make good candidates for Proco Rat clones? (For people whom the slow slew rate matters in those.)

I was thinking the same but I don't know how to test all the attributes that make the LM308 an LM308 if ya know what I mean. I do have some rat clones and spare chips. I may rig up breadboard buffer for testing the slew on my single opamps.

[duck_arse]

I usually set my signal generator to a 400Mv sign wave at 440Hz.

don't do this. 400 Megavolts will fritz those china's best, fer sher.

also, welcome to the forum.

He's correct, Mv = Mega vilts. 1 vilt = 1 picoVolt, so 400Mv = 400mV.
 

now, see, I almost went back to edit that post to chide about respecting the people the units get named for, and always using the capital V, but decided to instead 'quote' the OP. and it bit me on the arse. but ....

I was thinking the same but I don't know how to test all the atributes that make the LM309 an LM309 if ya know what I mean.

.... I don't know what you mean, the LM309 is a 5 Volt regulator.

[Mark Hammer]

Clearly, places like AliExpress are not going to invest in setting up fabrication plants of their own, so how do they get the stuff they sell so cheap?  I gather they purchase/redistribute stuff from manufacturers that did not meet QC specs.  Of course, those QC specs are not set on the basis of what works for us doofuses feeding 150mv signals with <10khz bandwidth, and reproducing it with speakers that roll off significantly above 6khz.  The chips direct from the manufacturer, that HAVE passed QC, can be expected to do whatever their datasheets say they can.  But since our collective needs (unless making a mic preamp for sampling nature sounds) are considerably less demanding, what gets sold by "budget" vendors in East Asia may be quite sufficient...assuming it is what he legending on the chip says it is, and assuming they actually work.  I bought a quintet of CA3240 chips to make Mostortions with and only one of them actually worked.  Another 10-pack of LM13700s all seem to work...so far.  But I have not tested all of them, nor do I know what contexts they might falter in.

[cornleader]

Of course, those QC specs are not set on the basis of what works for us doofuses feeding 150mv signals with <10khz bandwidth, and reproducing it with speakers that roll off significantly above 6khz.

True. My chinese resistors and film caps work fine for my uses. Even the Si diodes work ok. Electrolytics, chips and transistors. forget it.

But for my breadboard prototypes they "work". I bought thousands of parts from them, about 10000 resistors, 4 thousand caps, 1000 diodes all for about 30 bucks. I had to see lol.

[cornleader]

I usually set my signal generator to a 400Mv sign wave at 440Hz.

don't do this. 400 Megavolts will fritz those china's best, fer sher.

also, welcome to the forum.

He's correct, Mv = Mega vilts. 1 vilt = 1 picoVolt, so 400Mv = 400mV.
 

now, see, I almost went back to edit that post to chide about respecting the people the units get named for, and always using the capital V, but decided to instead 'quote' the OP. and it bit me on the arse. but ....

I was thinking the same but I don't know how to test all the atributes that make the LM309 an LM309 if ya know what I mean.

.... I don't know what you mean, the LM309 is a 5 Volt regulator.

I accednily press tha wr0nG nummbner butt fixxeded it reel qwik liek. Man u ARR fsat!!!!!

[PRR]

AliExpress are not going to invest in setting up fabrication plants of their own, so how do they get the stuff they sell so cheap?  I gather they purchase/redistribute stuff from manufacturers that did not meet QC specs.

Ali is just a middleman.
"Sellers on AliExpress can be either companies or individuals. AliExpress is different from Amazon because it acts only as an e-commerce platform and does not itself sell products directly to consumers. It directly connects Chinese businesses with buyers."  https://en.wikipedia.org/wiki/AliExpress

[cornleader]

I should have explained myself better. I didn't want to know the business model I was wondering what is happening in my 2 images lol. 

[R.G.]

We should talk about the use of "Chinese" as a synonym for "cheap and low quality". That's a popular reference, but it is not necessarily so.

A huge fraction of every manufactured goods is Chinese, both high and low quality. I've been dealing with Chinese manufacturing for over 20 years now, and the fact is that the Chinese manufacturers are businessmen. They will sell you what you want to buy. Historically, Western businessmen went to China for cheaper labor and lower costs, and demanded the lowest possible costs above all else. The Chinese responded with "OK, if that's what you want." It was a good fit for the labor available in China and their level of technical advancement. This spawned a whole generation of Chinese factories noticing that the cheapest stuff sold best and moving toward their customers' wishes. It also spawned super cheaply made knockoffs and counterfeiting.

I lived through the time of anything Japanese being thought of as inherently cheap; then through the era of American made cars and most other stuff being thought of as cheaply made and poor quality as compared to Japanese goods, especially cars. I had to sit through classes on quality manufacturing and "how the Japanese do it". Originally just a source of cheap labor, Japan worked its way into a major technical and manufacturing nation.

The bottom line is that buying from aliexpress amounts to buying from the cheapest possible source. Full stop. You get what you pay for.
You can get quality goods from China. You do it the same way you get quality goods from the USA, or anywhere else. You do a quality design, specify materials and processes and a finished goods quality testing program; then you keep on working with the manufacturer on a continuous basis to ensure quality stays up.
As an interesting note, the standard of living and wages have risen in China to the point that Chinese businessmen are off-shoring - moving manufacturing jobs and facilities to even lower-cost places to take advantage of the cheaper labor there.

[mozz]

Yes you can get quality goods from China, but they have a habit of slowly lowering the quality once you fly back to the US. Read the stories of tubes and other parts being made there. Quality was good, then slowly turned into junk. You would have to fly back over and complain. Quality would be back! Then slowly again, quality drops off. Fly over, find a new supplier, rinse repeat. It's well known that they do that. Show me low cost with quality from, China. Won't find it.

[marcelomd]

Hi,

I'm one of those who uses "chinese" as synonym for "cheap and low quality". I'll admit it's does not describe reality anymore. Iphones are made there, after all. Xiaomi is a very good brand too.

My father used o work at a cutlery factory. He was responsible for opening the "chinese channel". Off shoring of some product lines. Lots of travel back and forth to set everything up and a trip every now and then to make sure the quality was ok. This was in the late 90's, early 00's.  I remember the first videos were of the chinese partner's factory. Not much more than huts with half naked people handling hot metal with their bare hands.

The picture they had sent before the first visit was of a super modern warehouse-like building. Their name on a nice sign in front. The sign was theirs. The modern building was their neighbor, at the back of their lot.

Anyway. As far as I understand, and please, someone correct me, China has a "copycat" culture dating hundreds of years. Making knockoffs of foreign goods, specially if they sell as well as they do, is just one step away.