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| TL081 weird glitch |
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| iMo:
--- Quote from: sheisthedarkness on November 14, 2019, 05:34:16 pm --- --- Quote from: imo on November 14, 2019, 05:21:50 pm ---Try to wire a few kohm resistor from opamp's output against Vcc. It could be the glitch disappears.. --- End quote --- Just tried, no luck, same thing. How could this help exactly ? --- End quote --- The designers of that opamp forgot to layout the resistor on the die. Next time you should order that opamp together with option #1 - "1k resistor for crossover distortion elimination".. :-DD |
| Kleinstein:
--- Quote from: T3sl4co1l on November 14, 2019, 07:08:22 pm --- --- Quote from: sheisthedarkness on November 14, 2019, 04:43:50 pm ---Oh, well that's unfortunate. I didn't think something like that would be worth faking. --- End quote --- :-DD Rule 34 of electronics sourcing: if it exists, there's counterfeit of it! If it came from eBay, Ali or other unofficial source, assume it is counterfeit. Or salvaged. Doesn't matter what. And agree, looks like LM358 crossover distortion. Could be something even worse than that (a Chinese copy?), but not much worse without simply not working at all. Tim --- End quote --- In an other thread about fake OPs they did die photos, showing something similar to LM358 - probably a Chinese version. The performance was more like slightly better than expected for a real 358. Given that the OPs are not that expensive - they could as well sold the chips as what they are. There definitely would be a market for a cheap improved 358. Someone around here even got fake 0 Ohms resistors. So don't expect anything to cheap to get fakes. The cross over distortion is kind of a compromise taken for lower supply current. |
| Audioguru again:
Why bother adding an output resistor to eliminate crossover distortion when an LM324 or same opamps in an LM358 have trouble producing high audio frequencies due to the slow slew rate? They are also noisy (hisssss). |
| sheisthedarkness:
--- Quote from: Audioguru again on November 14, 2019, 11:28:27 pm ---Why bother adding an output resistor to eliminate crossover distortion when an LM324 or same opamps in an LM358 have trouble producing high audio frequencies due to the slow slew rate? They are also noisy (hisssss). --- End quote --- We're not certain what it is but I tested it with the 1k resistor from 0 to 20kHz, I did not see the crossover distortion appear again at any of those frequencies. I can't comment on noise as I haven't done any real testing but just by looking at it, compares fairly well to the real TL081 I have, which is why I was so dumbfounded ;D |
| wnorcott:
I don't get it because a TL081 only costs about 50 cents at Mouser electronics in quantity 1 and you know you are getting the real thing, from TI. Or if you wanty to go the discount route and don't mind to wait and wait, get them from Futurlec for 30 cents each. What is one minute of your time worth, that got wasted debugging bad chips? It's worth a lot more than 50c. I would not warm up my scope for fifty cents. |
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