Buying all sorts of things on ebay, I accidentally stumbled upon OPA627. This is a rather old, popular and high-quality operational amplifier, which is sometimes used in amplifiers by audiophiles (and not only). However, I was confused by the price - from the manufacturer (Texas Instruments / Burr Brown) they cost $ 16-80 (depending on version), and on ebay they were sold for $ 2.7, including delivery.

It was immediately clear that something was wrong there, but it was interesting to know what it was. I ordered 1pc, and for comparison - OPA627 in a metal case for $ 5, clearly soldered from somewhere. The results of comparing the insides are under the cut.

Received Chips

The plastic case had to be etched , and the metal - you can just cut it:

Compare

First the original. At least 4 laser-cut resistors are visible - it becomes clear where the cost comes from. Laser-tuned resistors are needed because in the manufacture of the microcircuit, the parameters of the components “float” a little, and in operational amplifiers they need to be coordinated very accurately. "Chinese" chip for $ 2.7. The laser-tuned resistor is only 1 here, however, the inscriptions AD (Analog Devices) and B744 are confusing - probably the model number. If we open the datasheet on the AD744 , then in the photograph of the crystal shown there we will see a complete coincidence.

What happened?

The Chinese brains and found a cheaper replacement for the OPA627 - it turned out to be the AD744. The AD744 has a similar speed (500ns to 0.01% accuracy), the same type (* FET), and external bias voltage correction is supported. The AD744 also has the possibility of external frequency correction - this is necessary for high-frequency applications with high gain, but this conclusion was simply not brought out (because it has no analogue in OPA627).

In this case, the AD744 is worse in noise (3 times) and bias voltage (0.5mV vs. 0.1mV).

The Chinese were not too lazy, bought AD744 in the form of crystals, packed and labeled as OPA627. I’m not sure that they made a lot of money from this - it is more like an economic diversion. But they could also stick something at the LM358 level - then it would be much easier to notice a catch…

So be careful and closely monitor the suppliers of the components - otherwise everyone will "optimize" for you :-)

PS. Also see previous series with fake FT232RL .