[IMSAI Guy] got some fake LM358 op-amps. Uncharacteristically, these chips actually performed well even though they didn’t act like LM358s. [IMSAI Guy] did a video about the fake chips and someone who saw it offered to analyze the part compared to a real LM358 to see what was going on. You can see it too in the video below.
A visual inspection made it obvious that the chip was probably a fake. X-ray analysis was a little less obvious but still showed poor quality and different internals. But the fun was when they actually decapsulated the part.
The die on the fake was labeled C665 on the die. The die was significantly different, but it isn’t clear why it wouldn’t be a more direct knockoff. It doesn’t appear that the device is cheaper to produce and it wasn’t a proper die rejected by a regular manufacturer.
If you want to see how the “C665” works, the original video that started it all appears below. The video shows the slew rate response was faster than a real LM358. The step response didn’t make a nice slope like the LM358 either. We hope he (or someone) will trace out the circuit and see what the circuit actually looks like.