LM386 getting HOT! Is that OK?

[smoguzbenjamin]

Hey guys (and girls )

I've got the Little Gem Mk2 running of 12v (regulated, I fried two 386s and found out that my 12v wallwart outputs 16.8v :evil: ) and the regulator gets pretty warm, but still OK to touch. The LM386s are at gain = 20, pins 1 & 8 open. They are getting hot!! So hot that it hurts to touch but not boiling (literally, water on my finger doesn't sizzle when i carefully touch the ICs) and performance doesn't seem affected. I was playing em for 45 minutes (The LG2 sounds good with a little fet preamp/buffer ) and they worked fine. Just hot. Is that normal?

cheers
Ben

[Torchy]

Dunno if its normal or not, but I built a LGII and whacked a Fetzer in front of it. Sound is cool, but both LMs run hot.

[maximee]

as far as i know from what i've read here there are different types of 386's...(four different types?)

the better (rarer?) ones I think were not running as hot as others...
so for the common 386 type it's quite normal to get warm...


but again, i am new to this and not 100% positive on that one

[lightningfingers]

If they are getting too hot to touch that will degrade their lifespan so it may or may not be worth getting a heatsink for them, it depends where you are and how cheap/availible they are. FYI mine run pretty hot too  

[Mark Hammer]

Well this is pretty much why I asked the question about heat sinks the other day.  Though "capable" of producing big outputs, these things (386) are not really intended to be used without heatsinks for more than headphones or else very modest outputs.

Funny, you know, all of this LM386 stuff starts to feel a little like all the how-high-can-you-overclock-your-P4 stuff after a while.

In any event, the smartest thing you can do for the moment is to increase the speaker load to 16R or something.  That'll probably keep it cooler.

[smoguzbenjamin]

I'm using a 4ohm speaker :twisted:

I'm using a JRC386D for one half, and an LM386N-1 ( :x ) for the other. I could use a big ole PC heatsink I've got lying around, whaddaya do, just use coolant paste like with PCs? Thing is, I've got a week to finish this up, I've been busy with school up until now and I'm on holiday for 4 weeks next thursday and I want to use this. I'll pack a set of extra LM386s in any case I can get them for 80 cents a throw pretty easily, my local store started stocking them! Yay!
I can't really increase the load to anything cos this is the only speaker I've got and (in true DIY spirit) I'm trying not to spend too much I could ring up my buddy and see if he can fix me another one of those speakers to bring it up to 8ohms but I doubt it :lol:

I'll try to fix up a heatsink. thanks!

[ExpAnonColin]

Funny, you know, all of this LM386 stuff starts to feel a little like all the how-high-can-you-overclock-your-P4 stuff after a while.

Amen.

You could try LM386-3's, could help.  Yeah, there certainly are too many varieties.

-Colin

[smoguzbenjamin]

I'd love to be able to get a hold of N-3s. Thing is, one shop has either N-1 of JRC386Ds and the other shop on rare occasions has 386N-1s only




... so how do you overclock anyways? :mrgreen: I've got a pentium 100 that's too slow :mrgreen:

[Paul Perry (Frostwave)]

If people want to recreate a particular exotic distortion machine, then sure, use the appropriate 386! but if you just want a little amp, there are millions of small flatpack audio amps available from surplus outlets that probably behave better.

[smoguzbenjamin]

It's behaving allright, just maybe alittle warmer than I'd expect. It was in the sun though, I'll take a look next time I play it, I'm working on the tonestack now

[ExpAnonColin]

If people want to recreate a particular exotic distortion machine, then sure, use the appropriate 386! but if you just want a little amp, there are millions of small flatpack audio amps available from surplus outlets that probably behave better.

Good point, Paul.  I was pretty amazed at the number of little all in one amps out there that Ansil sent me.  Do a search on National for an amplifier and you should find a pretty good wealth of them.

Smoguz-Move to the US.  :lol:

-Colin

[smoguzbenjamin]

Colin -

I wish I could, mate, honestly :lol:

[Paul Perry (Frostwave)]

Don't do it Smoguz! Come to Melbourne Australia instead, & eat fresh food!!

[smoguzbenjamin]

I think I'll stick right here then, exactly in the middle :mrgreen:

[zener]

:mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen:

I've just finished installing another fan into the CPU heatsink of my AMD Duron PC. This thing gets hot and it keeps shutting down my pc wheneevr it hits the temp limit of 60C. What I did is I installed another fan on the SIDE of the heatsink and reapplied some thermal paste. So now, there are two fans in the heatsink, one on top and the other on the side. My Duron is pretty cool now, it never get pass 45C.

Back to the topic. I also have the N-1's but they never get hot. I think, a small aluminum strip is enough to serve as a heatsink for that small chip. just put on top and secure it with a tape and should be enough. You can also put thermal paste if you want. You may also want to do something with PSU.

[Peter Snowberg]

I'm using a JRC386D for one half, and an LM386N-1 ( :x ) for the other.

I think that's the problem right there. I justy took a glance at the Little Gem Mk 2 circuit and noticed that there is no DC blocking cap on trhe outputs! :shock:

In a perfect world a zero volt input would result in an output from the first 386 which is at exactly 1/2 of Vcc. The second 386 would give an inverted version of this signal that would also naturally settle to 1/2 of Vcc. I know I don't need to tell you the world isn't perfect.

I'll bet that the two outputs are sitting at different voltages at idle and that is causing DC to flow through the speaker.

Getting rid of the cap is a nice thing in the Hi-Fi world, but this is a 386 amp so adding a good sized coupling cap isn't going to "damage" the audio much. I would add a cap in series with one of the pin 5 connections and the speaker. That will stop the DC and should reduce the heat (and power consumption). Try a value from 220uF to 1000uF. You can go smaller, but at some point the bass will be filtered out.

Take care,
-Peter

[smoguzbenjamin]

Damn Peter you're right! I looked straight over that. So do I orient both +sides towards the 386 or should I put the -sides to the inverting 386? Thanks!

[Peter Snowberg]

This is a spot where a non-polarized cap is called for. If you don't have a big NP cap, try two big caps in series with reverse polarity. I would go for 470uF to 1000uF for those because when you have two in series the capacitence will be cut in half.

Hey, while you're at it, you might want to put your meter across the pin 5 connections without the speaker in there. Any DC difference you see was being shunted through the speaker.  

Take care,
-Peter

[smoguzbenjamin]

OK, thanks peter, I'll go measure right now :mrgreen: Damn I don't have any big caps lying around. Thanks though!

edit:
I had some caps on an old PC PSU. They're 10v 1000uF (3x) and 10v 470uF (1x). I've soldered the - leads of them 1000uF caps together and a 1000uF and a 470uF, that gives two non-polarized caps of 500uF and 320uF respectively. That should be enough right?