Have you been wondering about ICs being real or not? IMSAI Guy in this video takes a look at a few opamps and shows you an easy way to find out for some 741 opamps whether they are real or not:
6 Likes
I had a few LM358 dual opamps lying around and I used them in one of my projects. Often times I use the TL072 but because these were pin compatible I thought, why no?
Unfortunately they didnât work properly. I found out that there is only one opamp in the ones I had in my circuit. Because I had some 14 of these devices I decided to try them all. I tried the LM358 pin configuration as per the datasheet, and also tried the pin configuration of a single opamp like the TL071.
The sad score:
- six of them contain one opamp which tested as an inverting amplifier did the job but the opamp pins are in an odd configuration (1 = out, 2 = neg in, 3 = pos in, 4 = V-, 5 = ?, 6 = ?, 7 = V=?, 8 = ?)
- two or them are broken, the opamp outputs a DC voltage when I feed it a square wave
- six remaining are also broken, they do not respond to anything.
Then I found some dodgy looking LM356 in my stash. I say âdodgy lookingâ because the print on the chip is not straight, and I would assume someone who has mastered making silicon dies should be able to get the type printed the right way. Of course I didnât check all the specs, but these turn out to work like one might expect from a single opamp.
Maybe 35 years ago it was more difficult to print the type of the chip on the casing than to make the chip.
Some weeks ago I bought some TL074 opamps. In fact I bought 3 batches of 10 pcs each from 3 suppliers. Given that Iâd bought some opamps in the past that didnât turn out to be working properly, I thought âbetter not get all from the same spotâ. Several people asked me whether the new ones were working. My reply at that time was: âTime will tell. As soon as I use them in a project Iâll find out.ââ
From the first batch of 10 Iâve now used a few and all appear to be working as expected. Note: I did not do any extensive testing, I only used them in some projects and there they appeared to work well.
This is a pic of an IC in batch 1. I found these to be unproblematic.
As soon as I have some experience with batch 2 and 3 Iâll report on those.
3 Likes
So far my bad experiences were all with chips I bought on eBay (especially the LF 398 sample and hold chips, there are lots of fakes out there). I prefer buying from well-known shops like reichelt.de, TME (https://www.tme.eu) and also RS (https://www.rs-online.com) when I need larger batches.
I donât really see the benefit of saving a few bucks when I have to check them all afterwards 
TL074 costs 35cents at Reichelt and 33 cents from an eBay seller who also sells antireumatic cream. I let you decide where to buy 
Of course, exotic chips are often expensive and one is tempted (or forced) to buy cheap ones from questionable sellers. I bought many of those from such sellers (e.g. LF 398, TP 2399, 3340, 3360 etc.) when I started building modular synths and there is a considerable amount of luck required to get what you want â lesson learned.
Luckily I have plenty of equipment at home to test these things but for beginners with a basic set of electronic gear I highly recommend sourcing components from reliable sellers. Fake or faulty components are frustrating anyways, let alone when youâre not able to test them properly.
4 Likes
In my stash I had some of these ICs. They are however not behaving to spec. Their outputs should be able to vary from rail to rail, but alas, they donât. So are they MCP6002s ?
1 Like
Do you have a signal generator and an oscilloscope? Itâd be fairly easy to find that out 
Or what do you mean by ânot behaving to specâ? If they do not behave to spec, they are either not MCP6002 or broken 
Btw. they are rated for a power supply range of 1.8V to 6.0V, keep that in mind.
1 Like
Their outputs do not go from rail to rail, but other MCP6002s (from another source) in the same circuit do.
I think you mean that they are not giving the upper/lower supply voltage on the output when the non-inverting input has a higher/lower potential compared to the inverting input. In that case, the chip is faulty (or fake).
Btw. a basic test (if you lack a signal generator and an oscilloscope) can also be done with a multimeter. Apply the supply voltages (within specs range), put e.g. the non-inverting input on ground and hook up a potentiometer with pin 1 on the low and pin 3 on the high voltage supply. The wiper goes to the inverting input of the opamp. Now check the output while you turn the potentiometer. You should see a flip of the voltage when you cross 0V (ground).
This is of course a very basic test and is not suited to check if the opamp works correctly for high frequencies.
If you have an oscilloscope but no signal generator, you can use your phone or the audio output of any device (e.g. use a 1000Hz tone from YouTube and hook up the 3.5mm jack to ground and the input). Then watch the output with an oscilloscope and try different frequencies. There are also signal generator apps for smartphones, which allow you to easily alter the frequency/waveform with some touch buttons.
2 Likes
Thx for the suggestions.
This is a small part of the circuit I was trying to use them in:
As you can see, when rotating the POT the output should go from 0 to 5V (assuming no input voltage at the CV in) but in fact it only reached 3.9V. After using a different MCP from another source, it covered the full 0 to 5 V range. REF-5 stands for -5V reference source.
If you want to really characterize an op amp, a fairly simple circuit for doing so is discussed here:
2 Likes
Iâve been using MCP6004 opamps in a project and noticed that their output when used as a non inverting amplifier does not reach the rail voltage. It stays 1 Volt below on all 4 outputs but should be able to approach it up to 25 mVolt according to the datasheet. I tried several of my lot and all the ones with the production info 1849AT2 canât reach the rail, the other one shown in the picture with production info 1610TSM can.
The MCP6004 can be powered to 6V. Assuming the â1839AT2â version is not an MCP6004 I powered it at -12 and +12 Volts and it works like a run of the mill opamp. No excessive power usage, the non inverting opamp circuits work well albeit the max output voltage at 10 Volts stays well below the rail voltage of 12V. So this chip definately works quite a bit out of spec, to say the least. Iâve not tried this with the 1610TSM because, as fate will have it, Iâve got only one of the latter and loads of the former.
I got one of those cheap op amp testers from AE and decided to test all the op amps in my stock. And together with the tester, I ordered a few more op amps from AE that the prices looked too good to be true. I figured I could test them on the spot. Who knows, they could test fine. After all I got a few working LM3600 and LM13700 from AE that worked fine in the oscillator jig.
The tester puts the op amps in a single 12V supply voltage follower configuration, two anti-parallel LEDs at the output, and injects a (selectable 10Hz and 200kHz) quare wave at the input. If the LEDs do not light at all, light only at the lower frequency, are very dim, or only one of the LEDs lights up, then you get a rough indication that there might be something wrong and that you should probably run a few more tests.
As a reference I had LM741, TL072, TL074, LM324, LM358, NE5532, LF353 and MC34083 that I got from reputable physical shops. The LM741, LM324, LM358, LF353 and MC30483 were vintage NOS parts, while TL072, TL074, and NE5532 were newer parts the shop got from another reputable supplier (tme.eu).
Results:
-
All the TL074 and TL072, and LF353 from ebay and AE (supposedly Texas Instruments) were tested as fake. The could not light the LEDs at 200kHz. Genuine TL074, TL072 and LF353 did not have such problems. When powered by a single 12V supply and the inputs were grounded, the output stayed at 0V, as a LM258/LM324 should behave. A genuine TL074 gave 11.5V at the same configuration indicating the typical phase reversal problem in those ICs.
-
LM833 (marked HLF, a Chinese brand) from AE also tested as fake. At 200kHz only one of the LEDs lit up, indicating that the op amp could swing down to ground but was not fast enough in the other direction, a tell tale that this was a rebadged LM358. For reference, the similar NE5532 worked fine. Additionally, when powered by a single 12V supply and the inputs were grounded, quiescent current was measured at 1.2mA which is too low for a genuine LM833 (should be 4-8mA).
-
OP07 (supposedly Texas Instruments) from AE were fake beyond any doubt. Genuine OP07s are likely too slow to light the LEDs at 200kHz anyway, so I tested resistance between pins 1 and 8 (the offset trim) where according to the datasheet there should be some resistance. Instead, I got an open circuit, just like I got when measured between 1 and 7 (supply) and 8 and 7 where there should be resistance as well. I also measured the quiescent current at 0.3mA which is too low for an OP07 (I couldnât find figure for 12V, but 4mA for +/-15V). I also noticed a huge offset at the output in the tester, where a genuine OP07 should have less than 0.1mV
-
OPA2134 from AE (supposedly Burr Brown) were also fake as well. First, they failed the op amp tester test at 200kHz, which a genuine OP2134 with its bandwidth should have passed. Second, measuing resistance between inputs and supply pins showed a resistance between 1-2M and a diode drop, indicating that the op amps were bipolar. If they they had JFET inputs like genuine OPA2134 they should have shown an open circuit.
-
LM741 (supposendly National Semiconductor) from AE were also fake. Genuine LM741s should be too slow for the 200kHz test, so I measured resistance between pins 1 and 4 and and 5 and 4 (offset null pins to - supply). The ICs showed an open circuit when the LM741 datasheet shows 1k resistors in between those pins. As a reference, the genuine NOS LM741 indicated 1.2k. Quiescent current was also measured around 0.3mA which is too low for an LM741, although the genuine LM741 also measured low (which could be due to being LM741J military variant in ceramic package).
I also got a few RC4558 from ebay and LM258 (LM358 with wider temperature range) from AE, which are likely fine although I need to do a few more tests.
Now I got my money back on those last few orders but spent a lot of time testing, etc. I did not mind the time spend as I treated it as a learning experience, but I will likely not do it again.
At this point, one might ask if itâs really worth buying any ICs from ebay and AE at all. The thing is that for most people outside the US buying from Mouser, Digikey or Jameco is not an option due to the huge cost of postage, added VAT and import fees. Buying from Tayda or shops from the UK (thanks to Brexit) also incurs VAT, import fees and a long hold up at the customs. Even shops within Europe will charge you more than 10 EUR for a small package with a couple of ICs. Considering these, ebay and AE sound attractive especially since you can combine your order with other components that are usually fine and sold at very competitive prices (IC sockets, headers, 1% resistors, ceramic capacitors, 4148 diodes, LEDs, etc). Unless you like the risk and enjoy spending time testing, itâs not worth it.
4 Likes
@K.ostas Thx for this overview ! That is a great thing to have. You mention sellers in the EU, Iâve bought some stuff via tme.eu, just wanted to mention them because people might not know them. It is a huge seller and I only learned that they exist maybe a year ago.
If there are so many fakes around I wonder what the business model of the makers is. You need quite a lot of expensive and complicated technology and engineering expertise to make an opamp even if it is fake. And knowing that people who look into the opamps produced will find out that they are not up to spec, you will have unsatisfied customers. So, how long will you be fooling people into buying stuff who will then never buy from you again?
Could all of these opamps simply be rejects that get ârebrandedâ or ârelabeledâ ?
1 Like
Yes, TME (based in Poland) are great. They charge 10.50 EUR min postage, so it doesnât make sense if you just want a couple of things. Fortunately, one of the local shops around here has TME as their supplier so I can order via them anything from the TME catalogue (with some reasonable surcharge plus VAT).
It took me a couple of years to find the right combination of local shops / AE / online shops to get everything I need. To that, I should also add local ads (garage sale type) about spare parts/electronics and salvaging parts from old electronics which can be a great source for reference parts like JRC4558 or bulky items like transformers.
As for the business model in faking stuff for pennies, we have to understand that commerce in China works on extremely tiny profit margins because they sell in bulk quantities that are simply impossible elsewhere. This video explains it pretty well I think.
2 Likes
Thatâs interesting. I also had some TL074 from AE but they were ok. I just tested a few random ones with a signal generator and an oscilloscope and they behave fine.
How reliable are these cheep opamp testers? Have you cross checked with a signal generator and oscilloscope? Just curiousâŠ
1 Like
The tester is fine for what it is. I checked with an oscilloscope and they produce a clear square signal roughly at those two frequencies 10Hz and 200kHz. Other than that, they place the op amps in a single supply voltage follower configuration with resistor-LED at each output. Power filtering, 100nF at the supply rails etc. All standard stuff.
I did further tests, those mentioned in the post, plus a few more. There is no way the AE and ebay TL074s, TL072, LF353 are genuine. They fail at high frequencies, but also, they do not have FET inputs, they do not exhibit phase inversion and instead swing down to 0V like a LM324/LM358. In the other op amps pinout resistance, quiescent current, offset voltage are all way off.
You might have been lucky and gotten a batch which is real. I got working LM13600 and LM13700 from AE (although, itâs anyoneâs guess if the 13600 are 13700 or vice versa!) but not from ebay, so anythingâs possible.
1 Like
I should also emphasize that, for TL074, TL072, LF353 and LM741 I tested them against genuine parts. And I tested LM833 against genuine NE5532 as a benchmark. The test results were day and night whether on the tester or elsewhere.
1 Like
On the other hand, the LM359 dual programmable Norton op amps that I got from AE definitely look the part, with four different date codes from 1995 and 1996. Most importantly, I tested them on breadboard as a square wave oscillator (Figure 49 off the datasheet), and I got them to oscillate at 2MHz. Their pinout is really unique, with single supply, ground per amplifier, programmable current input and output, and external compensation pins, so I am certain these are LM359.
So itâs a gamble.
2 Likes
If you have any issues with op amp current handling and output I can heartily recommend a deep dive into op amp stacking. Aka.âPiggybacking.â
Literally sticking one chip on top of another. Done properly this can double the output current and lower the noise floor. Youâll need stabilizing resistors on the inputs to minimise overheating and a decoupling cap on the power. And just like matching transistors, youâll need to find a chip with a similar voltage offset. Similar chips will give you a warmer tone, chips that are too dissimilar will fight for power and overheat and oscillate at a high frequency (horrible noise).
Stacking halves the input impedance so take care and study how any preceding circuit may cope with that.
This was a massive fad in the 80âs for everything from preamps to tube screamers and other fx pedals which back then all sounded the same. (True! I was there! Give me a DX7, an active pickup guitar and a boss CE-2 and I can play the 80âs for you! I wonât wear the jacket and leg warmers though as some things need to die and stay dead.)
Go on! Stack em high!
2 Likes
Top Tip:
When buying ICs or any active components where you are not sure of the provenance, keep them in a box marked âQuarantineâ until you have time or need to test them. You donât want them mixed up with your legitimate stock.
If you buy from eBay or Temu, etc., you have to assume they are counterfeit until testing proves otherwise.
The only time I buy such ICs are as part of a kit. For example, there are handy pre-amp kits on eBay that are good value for the PCBs alone, but the ICs in the kits end up in the bin.
It amazes me how often Chinese products spoil the ship for a haâpworth of tar.
1 Like