https://hackaday.com/2022/11/27/a-practical-discrete-386/ Skip to content Logo Hackaday Primary Menu * Home * Blog * Hackaday.io * Tindie * Hackaday Prize * Submit * About * Search for: [ ] [Search] November 27, 2022 A Practical Discrete 386 22 Comments * by: Jenny List November 27, 2022 * * * * * Title: [A Practical Discrete] Copy Short Link: [https://hackaday.com] Copy [discrete-l] There are some chips that no matter how much the industry moves away from them still remain, exerting a hold decades after the ranges they once sat alongside have left the building. Such a chip is the 386, not the 80386 microprocessor you were expecting but the LM386, a small 8-pin DIP audio amplifier that's as old as the Ark. the '386 can still be found in places where a small loudspeaker needs to be powered from a battery. SolderSmoke listener [Dave] undertook an interesting exercise with the LM386, reproducing it from discrete components. It's a handy small discrete audio amplifier if you want one, but it's also an interesting exercise in understanding analogue circuits even if you don't work with them every day. A basic circuit can be found in the LM386 data sheet (PDF), but as is always the case with such things it contains some simplifications. The discrete circuit has a few differences in the biasing arrangements particularly when it comes to replacing a pair of diodes with a transistor, and to make up for not being on the same chip it requires that the biasing transistors must be thermally coupled. Circuit configurations such as this one were once commonplace but have been replaced first by linear ICs such as the LM386 and more recently by IC-based switching amplifiers. It's thus instructive to take a look at it and gain some understanding. If you'd like to know more, it's a chip we've covered in detail. * [share_face] * [share_twit] * [share_in] * [share_mail] Posted in PartsTagged audio, audio amplifier, lm386 Post navigation - Portable Commodore 64 Lives! I Need A Hackation - 22 thoughts on "A Practical Discrete 386" 1. ONV says: November 27, 2022 at 5:15 am Is this a clickbait title? A discrete LM386 is interesting but a discrete Intel 386 would be seriously cool :-) Report comment Reply 1. nono says: November 27, 2022 at 5:30 am i had exactly the same feeling when i read this : "not the 80386 microprocessor you were expecting but the LM386" It's just borderline abuse, or dishonest. Report comment Reply 1. Ostracus says: November 27, 2022 at 5:49 am It shows how assumptions* color our everyday interactions. A lot of readers being into electronics should know better. *Created by effective marketing no less. Report comment Reply 2. Feinfinger (kinda angry here) says: November 27, 2022 at 7:29 am "not the 80386 microprocessor you were expecting but the LM386" They did it on purpose. I think that just underlines lack of respect for the readers! Let them burn in clickbait hell! Report comment Reply 1. Michael Black says: November 27, 2022 at 7:41 am I wasn't confused. Though perhaps because Isaw this somewhere else first. But like I said, I remember when the LM380 was new, and better than what came before. So I knew about the 386 before any 16 bit processor. And it's silly to make ICs put of transistors.Transistors on ICs are close to free, so evenanaudio amplifier will have more transistors than if you were building from scratch. Allkinds of tricks in ICs that are because it's an IC Report comment Reply 2. [EGO] says: November 27, 2022 at 9:17 am I find some of it interesting. I have quite a few hobbies /interests, and get a kick out of different model numbers, etc. meaning different things in the different hobbies. Report comment Reply 3. blaisepascal2014 says: November 27, 2022 at 8:22 am It would be more interesting if the linked article actually built a discrete LM386. Bill said he was going to build a discrete LM386, but just designed a push-pull amp, which he admits is only part of what's in a 386. Dave designed an amp, and made no claims it was based on the 386. The schematic in the Hackaday picture isn't in the linked article, either. Report comment Reply 4. ytrewq says: November 27, 2022 at 9:10 am >Is this a clickbait title? Of course it is, although the schematic shown was a dead giveaway about which part it was referring to. About the LM386, that is not a very good part wrt noise, distortion and power efficiency, it just gets the job done very cheaply. If you already have some in your drawers it's fine to use it, but if I had to buy it for some projects I'd rather go to newer much better parts. Report comment Reply 2. nono says: November 27, 2022 at 5:33 am building expectations - I, as most of readers, was immediately imagining a dense forest of transistors emulating the inner guts of a 386 processor - to raise interest then deceiving people might be fun for the authors, but it's a flawed editorial practice. Report comment Reply 3. Sebastius says: November 27, 2022 at 5:38 am Ha i smiled with the title, being puzzled that a discrete 80386 would be impossible and smiled some more with the joke. Don't be so harsh and offended at a little play. Great article and yes you got me! Report comment Reply 1. Jenny List says: November 27, 2022 at 5:42 am Somebody gets it. :) Report comment Reply 2. Foldi-One says: November 27, 2022 at 5:56 am Indeed, nothing wrong with a bit of fun, and its always nice to see the usually hidden analogue circuits revealed so its quite a nice useful short joke article. However it didn't get me, but that is just because 386 didn't immediately mean anything to me either way, it probably should have though - so I'm just going to put it down to lack of sufficient thinking lubricant. Clearly need anther cuppa. Report comment Reply 3. Alexander Wikstrom says: November 27, 2022 at 6:05 am 275000 transistors for the 80386 is however not too unreasonable. With sot23-6 packages containing two transistors each, it wouldn't be too huge. At 3x3.2 mm (including its keep out zone) in size then 275k of these would just be 2.64 m^2 of single sided board. We can reserve the backside for the "few" passives that will be needed. But it isn't too excessively huge to be fair. If we make it a stack of boards, then it can be much more compact. (and likely faster.) If using 1.2mm thick PCBs and 1.1mm tall sot23 packages on either side. (passives are likely thinner) Then it is just 3.4mm per board. So if we want it A4 sized, 295 x 210 mm per board. Then it will only be 146.2mm tall. Not all that huge to be fair. Except, the boards will need to have space for interconnects linking them together. So might need to add a few more boards to the stack up to space things out. In the end. It isn't impossible. Just silly. Report comment Reply 1. Sebastius says: November 27, 2022 at 6:23 am Well i greatly desire the 6502 made of basic mosfets etc by Tubetime, but i want to solder it myself as a "nice" kit :P Report comment Reply 2. Joshua says: November 27, 2022 at 11:47 am I think the same. It's quite some work, but doable. Size would be that of a wall closet - if regular 2N2222 or BC548 were used. SMD types could reduce size to that of a closet. A slower clock rate for such a discreet version could be used, also. A few hundred KHz to a few MHz, maybe. It could still be quicker than an 8086 at same clock. Thus, totally usable to run DOS, PC-MOS/386, Windows 3 or PC GEOS. But of course, the title/headline was a trap. My first thought was: "386 processor? No wait, that be 80386. They mean an LM386, surely.. Old people often omit the LM prefix.." Report comment Reply 4. -jeffB says: November 27, 2022 at 6:22 am Does this mean I'm the ONLY one who read the title and thought "hmm, 386 - was that an amplifier or a variable voltage regulator?" Report comment Reply 1. David says: November 27, 2022 at 7:27 am Nope. Not the only one. :-) Report comment Reply 5. Michael Black says: November 27, 2022 at 6:28 am I remember when the LM380 was the neat IC audio amplifier. Report comment Reply 6. elwing says: November 27, 2022 at 8:59 am nice, I don't think I ever saw a NPN - NPN output like that, I'm more used to the NPN-PNP pair... I wonder why it's been build like that, anyone knows? Report comment Reply 1. hartl says: November 27, 2022 at 12:26 pm This is a complementary output stage, but back then it was not possible to create NPN and PNP with similar characteristics on one chip, PNPs always had higher internal resistance and could not carry enough current. The NPN-PNP pair (also called Sziklai pair) behaves like a PNP, but a better performing NPN does the heavy lifting. This method was also used in many discrete circuits with beefier NPNs like the 2N3055. Report comment Reply 7. Will says: November 27, 2022 at 9:08 am As a diy guitar pedal enthusiast, I knew exactly what this article was about ;) Report comment Reply 8. Bob The builder says: November 27, 2022 at 10:41 am Which prick wrote this headline?! Report comment Reply Leave a Reply Cancel reply Please be kind and respectful to help make the comments section excellent. (Comment Policy) This site uses Akismet to reduce spam. Learn how your comment data is processed. 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