Electronics > Beginners
TL07x, TL08x eBay fakery
John B:
This is probably a "well duh" moment, but is still worth documenting. It would seem that eBay sourced TL op amps have a radically different architecture to what they're supposed to. So, not even factory rejects, but probably some other op amp with a TL label on it.
This follows on from a comment here: https://www.eevblog.com/forum/beginners/adding-filters-to-class-ab-audio-amp/
that TL op amps shouldn't exhibit crossover distortion. Below is a comparison of an eBay sourced "TL072CP" and "TL082CP", vs an LCSC sourced TL072CP. Each op amp is powered at +/- 5V, +/- 15V, with a 10k load to ground. All configured as a non inverting buffer.
eBay "TL082CP" @ +/- 5V. Note crossover distortion around -1V.
eBay "TL082CP" @ +/- 15V. Note crossover distortion around -1.5V.
eBay "TL072CP" @ +/- 5V. Note crossover distortion around -0.8V.
eBay "TL072CP" @ +/- 15V. Note crossover distortion around -1.6V.
LCSC TL072CP @ +/- 5V. No crossover distortion, but note the distortion/non linearity at the bottom of the sinewave.
LCSC TL072CP @ +/- 15V. All G :-+
eBay "TL082CP" and "TL072CP" on the left, LCSC TL072CP on right. Apart from differences in labelling and package shape, the legs on the LCSC item are made of a stronger metal than the eBay ones, which are softer.
Audioguru again:
Your oscilloscope or your signal generator is digital with a limited number of steps that cause the steps on the waveform. The top and bottom are supposed to have a gradual curve that the product cannot produce. The sides of the waveform also look torn apart with reduced resolution.
John B:
Here's a closeup of the crossover distortion on the eBay "TL072CP" +/-15V:
More pics to follow.
John B:
Here's the lower part of the waveform on the LCSC sourced TL072CP. This experiment isn't operating inside the recommended supply range and common mode input range, so I'm not claiming it's amiss, but I just didn't expect this behaviour. This distortion isn't at the top of the waveform. Yellow is op amp output and green is signal generator.
+/-6V
+/-5.4V
+/-5V
+/-4.8V. Finally into clipping.
floobydust:
Hard to tell if it's an imposter or a reject of an original part. You can measure quiescent current and see if the output stage is under biased, but slew rate would tell lots too.
There are some generic op-amps out of china that get used for counterfeits.
I would send them to Zeptobars in Moscow, as a fake/genuine comparison, with the beautiful die shots they do.
There is an ST TL072 die-shot and I see no laser trims. OP265 fake was a NE5532 inside.
https://www.eevblog.com/forum/reviews/chinese-fake-op-amps/
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