Electronics > Beginners
Odd Glitch In Waveform
magic:
--- Quote from: radiolistener on February 10, 2020, 11:17:14 pm ---I caught exactly the same issue with fake Chinese operational amplifier.
--- End quote ---
I recently got an AliExpress coupon and spent it on some cheapest jellybean opamps for shit and giggles.
Long story short, they were all LM358 inside or RC4558 for the "audio" parts. You just can't buy that stuff from there. And lots of people import them and resell in Europe, so domestic auction site sources should be suspect too.
codingwithethanol:
Thank you guys for all the feedback! So I took into consideration some people in the thread said:
I first tried the original suggestion by @Nerull, I added a 1k and 100k pot in series as a dummy load, but I didn't see anything similar to what was shown in w2aew's video. The glitches sort of "flattened out" and then the output started clipping.
@rstofer and @Cerebus mentioned the 741 being used with at least ±10V, so I adjusted my PSU to 20V so the split would be -10V +10V.
@rstofer mentioned that the resistors for the voltage dividers needed to be lower so I used 1k as suggested.
These modifications didn't affect the output in any way, so finally, since I purchased these off of Ebay from a dubious chinese reseller, i'm going to take into consideration what @magic said and assume these amps are just janked clone ripoffs. I have some other amps which I want to try out, I actually got some ceramic chips from an old bag of mixmatch parts I got a while ago, so I'll try them next.
codingwithethanol:
Success! I skipped the ceramic chip and tried an RC4558, which the datasheet says is basically a dual 741 and it works perfectly, as seen in the attached picture. Gonna try to use it as a mic amp next.
magic:
Dual 741 was 1458 and 4558 is a slightly different animal.
4558 is what goes into all those NE5532's on auction sites and fetches 100% positive feedback so it's clearly good enough for audio :D
codingwithethanol:
@magic Just rigged up electret mic and cranked the gain and it works beautifully! I have an offtopic question if you don't mind, I fed the opamp output to a logic level mosfet to try to power a speaker but the fet cooked for some reason, also I tried hooking the opamp output directly to the speaker but i just got a wierd clicking noise. After that I tested the speaker with my function generator to make sure it wasn't faulty and it's fine so how would you go about this? End goal of this whole thing is to make a mini megaphone, I have these cute little speakers I ripped out of an old dell thing (See picture) that I wanted to use in a project so why not this.
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