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I am not an electrical engineer, but I am curious enough and my mind tells me to make a radio circuit.

Now I am into it, so to make one, I need some components, but before that so that I can be a little more into basics of the working of the device, the only device I can't find an explanation for is the LM386 IC.

It is an audio amplifier but its pin-out is not that clear. It shows a simple triangle but no information.

What is it? A logic gate, another IC?

Please explain to me how the LM386 works.

JRE
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SHikha Mittal
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  • Copy and paste the picture that has the triangle from the [data sheet](https://www.ti.com/lit/ds/symlink/lm386.pdf?HQS=TI-null-null-sf-df-ds-null-wwe) – Andy aka Aug 10 '20 at 17:18
  • Just a general remark: The LM386 is a **terrible** amplifier. Really, no matter what you do, there's better ones, that aren't much harder to get. The LM386 was invented 1969. That's 51 years in the past. It sounds terrible, and was replaced by more reliable, more efficient, easier to use correctly, and most importantly: better sounding ICs since then. – Marcus Müller Aug 10 '20 at 17:55
  • @MarcusMüller There are better, mostly in the pre-amplification side -- which really should be designed for the input source and not just developed generically if you want the S/N as good as possible. There are better in the sense of being bridged (two amps inside) and therefore easier to generate more power from a given rail voltage. But it and the LM380 have global NFB that can be adjusted and I'm curious what class-AB amplifier ICs you like, in particular. (I don't ever use the LM386. I'm just curious what class-AB IC you like.) – jonk Aug 10 '20 at 18:24
  • SHikha, see [this LM380 discussion](https://electronics.stackexchange.com/a/273901/38098) for some thoughts. It's not the LM386, but you can compare the schematic with the LM380's by referencing the schematic on the LM380 datasheet. You'll see a lot of similarity. – jonk Aug 10 '20 at 18:27
  • @jonk truth be told, I grew up dissecting discarded car radios – so, a lot of 1980's ~20 W output power TDA-series ICs. My first car had a badly botched together amplifier in place of the cheap car radio that it came with. But AB: you can't really make an incredibly efficient class-AB, can you ;-) These days, I'm kind of fond of the highly-integrated class D amplifiers with switching frequencies in the hundreds of kHz; while the need for external filtering makes things more complex, I feel that it's become feasible for far lower-reaching ranges of power. Also, after all my other projects are – Marcus Müller Aug 10 '20 at 18:30
  • done, I'm definitely going to design a digital bus system for hamburger-sized class-D amplifier+speaker+microphone+ADC/DAC+DSP units and a central processor, which allows for self-calibration, where a channel sounding algorithm sounds the room and calculates an impulse response correction per speaker, which the individual units apply themselves. Right. After all the other things I have to build are done. It will be a tremendous succes, around 2068. – Marcus Müller Aug 10 '20 at 18:34
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    @MarcusMüller I definitely use the TDA family. My first was the 1 W TDA8551. The class-D are way out of the capability for many hobbyists to correctly design for, though they can just use them. That last project you describe sounds like over-kill to me. But then I'm old enough now that hearing is declining and really nice acoustics into my brain is no longer much of a possibility. – jonk Aug 10 '20 at 18:49
  • @jonk overkill is just one of my many modes of operation. Think of it not in terms of being meant for your nicely dampened living room, where places you want good sound are limited and also, human hearing still compensates for the frequency-selectivity of that resonant cave, but think of e.g. a pub or something with e.g. a stage on one end, rooms attached to each etc, where things get ugly unless you strategically place absorbers to avoid the worst of standing waves. Being overkill is a bit the point there: there's almost certainly not a perfect solution for an arbitrary room where people move – Marcus Müller Aug 11 '20 at 09:01
  • arbitrarily, but if you have enough degrees of freedom (i.e. enough speakers), you might actually make a difference. Also, truth be told, I was starting with a pretty different idea: Equip the ceiling and walls of a well-padded room with arrays of speakers, do wavefront synthesis so that literally, your system can whisper into one persons ear while the other person doesn't notice and the third is having shivers since theres a wolf growling, *always behind his back*. Then I realized the good sound distribution problem is at least as mathematically interesting. – Marcus Müller Aug 11 '20 at 09:05
  • @Marcus Müller is lm4862 good? – SHikha Mittal Aug 11 '20 at 14:52
  • @SHikhaMittal how are we supposed to know? you've never even specified what you needed it for. On the contrary, you use the [tag:rf] tag, which would indicate you're looking for an RF amplifier, which all these amplifiers are *not*. – Marcus Müller Aug 11 '20 at 14:59

3 Answers3

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The LM386 is an IC. The triangle is just a symbol use on a schematic diagram to represent the IC.

If you consult the manufacturer's datasheet for the LM386, you should find a full description and schematic of the internal circuit, and also a description of the physical package of the part, with the dimensions and pin locations.

Peter Bennett
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The LM386 is an audio power amplifier. "Power" in this case usually is less than 1 watt. In a sense it is a specialized version of an operational amplifier, so it usually is shown on a schematic with an opamp-like symbol.

Here is the datasheet from the company that invented it: https://www.ti.com/lit/ds/symlink/lm386.pdf

Only one of the schematics in the datasheet shows a decoupling capacitor across the power pins, but it is critically important that it be there for any/all circuits. The capacitor(s) should be as close as possible to pins 4 and 6, with the shortest possible leads. I recommend a 0.1 uF ceramic and 10 uF electrolytic in parallel. All audio power amp chips are very sensitive about this.

AnalogKid
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  • I don't think TI invented LM386 though. – Justme Aug 10 '20 at 17:34
  • @Justme no, that was Motorola. 1969. – Marcus Müller Aug 10 '20 at 17:53
  • @MarcusMüller - Are you sure it wasn't National Semiconductor. The LM prefix is used for all their devices (I think it is an acronym for Linear Monolithic). Motorola numbers all began with MC. TI now owns National Semiconductor. – Kevin White Aug 10 '20 at 23:13
  • National invented the LM386 as a stripped-down version of the LM380. TI bought National and all of their designs and documents. The old Motorola part has the same number, but I don't think it is the same part. The LM385 we are talking about is not something for an automotive fuel injection system re-purposed for consumer audio. – AnalogKid Aug 10 '20 at 23:44
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Here is a pinout diagram of the lm386. And I believe this is its most general format.

lm386 pinout