EEVblog Electronics Community Forum
Products => Other Equipment & Products => Topic started by: SnipTheCat on September 11, 2015, 06:30:37 pm
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Hi,
I just got a bunch of op-amps from China (I'm located in Thailand), After doing some test I see some very disappointing results... Test was done with a 15Khz square wave, op-amp gain set to ~5 (input is 400mV pp) (op amp powered with +/-12V supply)
See the attachments:
The first and the worst is a LM358P (not sure if it's genuine or not) but it performs close to / as worst as the datasheet say it should.
The second is a LM358P ordered in china for like 3 USD / 100 pieces, it has a slew rate of ~5V/µS which is over 15x what is should, I see spikes around edges, not sure what they mean. This one is obviously a fake which performs better than expected.
The third is a NE5532P (cost like 6 USD / 100 pieces), slew rate is ~1.25V/µS which is far under what it should be (9V/µS according to the datasheet). The performances look pretty similary to a genuine JRC 4558.
The fourth, and the worst... the "TL072CP" has a slew rate of ~0.43V/µS, I did some extra tests with higher frequency but at 50Khz, the gail dropped like crazy, I'm sure it has performances worst or equal to a genuine LM358...
I then wanted to double check the results and made a small circuit with inverting configuration with 2.2k Ohm on the inverting input, and 4.7k Ohm between inverting input and output for a gain of ~2.1, op amp was powered with -12/+12V supply, input signal was square wave @ 15, 50 and 100Khz generated by an AD9850 module controlled by an arduino, generating a square wave of 1.3V pp amplitude with slew rate measured > 100V/µS on the oscilloscope, results were exactly the same.
Am I correct to say those NE5532 and TL072 are garbage? What about the oscillations seen on the edges of the "fake" LM358 op amp?
Thanks,
David.
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Why not ?
http://zeptobars.ru/en/read/OPA627-AD744-real-vs-fake-china-ebay (http://zeptobars.ru/en/read/OPA627-AD744-real-vs-fake-china-ebay)
http://zeptobars.ru/en/read/Nordic-NRF24L01P-SI24R1-real-fake-copy (http://zeptobars.ru/en/read/Nordic-NRF24L01P-SI24R1-real-fake-copy)
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Another suggestion would be to feed the input signal to one of the other scope channels just to make sure the other waveform glitches are not present in the input signal. It allows easy comparison then.
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Yes I did test the input signal of course, and it was perfectly square.
I confirmed the slew rate results by using the op-amps as comparator and switching them from -Vcc to +Vcc (fake LM358 gets almost 6V/µS ! 20x its specs).
About the GBW, the fake TL072 gives a triangular wave with gain ~1 with a 100Khz sine wave at the input and a gain of 10, not sure how to calculate the GBW but it's so bad it's not even necessary to bother...
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They are even bothering to fake Low Drop Out Voltage regulators at a few cents a piece! The price hardly justifies the effort in adding the dodgy marking to the part.
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This sounds like an opamp identifier could be an interesting project to consider... you could use it to test parameters and match them against a database to determine what it really is.
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How to test opamps to see how they perform?, would it be possible to make some setup to compare it to an original one? (ie, buy original ones of the types one think is fake, and test them together in some setup/jig)
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Do you think can anyone make any money doing these for fake in Thailand? The wage in China probably is about the same as Thailand or more now.
Worse you can get are the rejects, or used parts.
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China is still cheaper than Thailand, and most electronics sold here come from China, there used to be a lot of major brands factories located here (such as hard disk manufacturers), but a lot moved out after the floods end of 2011. I recently visited a PCB assembly factory here in Bangkok, the engineer I talked to told me they were 200 employees now but a few years back they were over 3500 (When I visited they were currently making PCBs for Sanyo), he told me that they lost most of their business to China.
Do you think can anyone make any money doing these for fake in Thailand? The wage in China probably is about the same as Thailand or more now.
Worse you can get are the rejects, or used parts.
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My vote goes for tested rejects. They win, you lose.
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How desperate do you need to be to fake the cheapest opamp ever?
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About 5 years ago I bought 10 7805L regulators from a ebay seller in Thailand. They all worked but everyone of them was off by at least +/- 0.5 vdc, none inside that range. I've stayed away from Thailand sellers sense.
Seems obvious to me that they were devices that failed final test and entered the gray market. Haven't' had a problem with Chinese products other then some fake FTDI devices on arduino nano clones that failed to work once FTDI updated their driver making these fake unusable.
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FYI, I've looked under the hood of these:
https://zeptobars.com/en/read/Ti-NE5532-real-vs-fake-opamp
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Truly amazing people are counterfeiting such cheap parts. I guess they make it up in volume. Talking of Thailand sellers, isn't Tayda Electronics from Thailand? They always appeared very reliable to me and find it hard to believe they would go with that. It is where I source my TL07x op-amps. Hmmm...
/Pedro
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The third is a NE5532P (cost like 6 USD / 100 pieces), slew rate is ~1.25V/µS which is far under what it should be (9V/µS according to the datasheet). The performances look pretty similary to a genuine JRC 4558.
I tried some NE5532P that I have just received from a Chinese ebay seller in a power supply design I have been working on.
These parts have a maximum slew rate of about 1.5/µS instead of 9V/µS when I test an NE5532P that I got from Rockby Electronics.
The NE5532P from China don't look like the usual fake parts that I have received in the past where the original markings have been removed and then marked as different part.
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Hi,
I just received 15pcs BURR BROWN OPA2134 dual opamps from China.
A quick test in one of those basic functionality testers showed them as tl082, at least a dual opamp.
But, I decided to test some more:
I put together a 10x amplifier circuit, using a dual +8/-8 Volt power supply, and fed a nice, 1kHz square wave into it to see what slewrate I could see....
The opa2134 should have a 20V/uS slewrate, but I got 2.5V/uS 😱
When I tested a TL082 I got around 10V/uS, roughly as specified
and with a LM833 also around 10V/uS, also as specified.
Ergo: these opa2134's are as fake as fake could be??
Saludos,
Leo