Can I make a simple LM386 portable amp that is battery run with multiple outs?


I would need it to have at least two outs but would prefer four outs. I also would need right/left balance and a volume control.  I am going to use this in a waterproof enclosure to make it work for camping and floating.  I am hoping to have this thing work off of an mp3 or any other 3.5mm jack.  If it will be better to use two of these amps just let me know because it would not be a big deal to include another one in the enclosure. Also I found away to make the LM386 drive more bass for a sub on runoff but if anyone has more input on this subject let me know.  FYI I am a rookie, first timer, at this so any links, guides, or detailed instructions would be great.

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David976 years ago
Setting the curcuit in exoxy resin will make the amp itself warter proff. For the speeker you may want to make a container with a thin peice of plastic over it.
Well, I had a nice answer for you last night, but it disappeared when I went to preview it. Here I go again...

While you can use the LM386 for amplification, try to think of it in the vain of "transistor radio" loudness - enough for personal listening within 5 - 10 feet at a relatively quiet campsite.

That said, take a look at the LM386 datasheet here. Scroll to page 5. You'll see that there is a version with bass boost near the bottom of the page. You'll also notice that there are different gain versions presented there. Try them and see which works best for you.

As has been stated , the LM386 is a mono amp and you will need 2 for stereo. See this question for my take on stereo / subwoofer setup using a total of 4 LM386's.

Volume control is pretty easy. Place a 20K ohm dual potentiometer, audio taper, in the input signal path. One outside lug to the audio in, the other outside lug to ground and the center lug (wiper) to the audio in to the LM386. Do this for the left channel on 1/2 of the "pot" and the right channel on the remaining 1/2 of the pot.

Balance is even easier. Place a 20K ohm (single) potentiometer, linear taper, between the inputs, either before or after the volume "pot". One outside lug to the left input, the other outside lug to the right input and the center lug (wiper) to ground.

Another option you might want to do is put a DPST (Double Pole Single Throw) switch inline with the "bass boost circuit" to turn it on or off. If you cannot find a DPST switch, just use s DPDT switch. It'll work, you'll just have an extra throw in there - no biggie.

Ok, now to your question as to what else you can use. Try a search for the "power" or wattage amp you want. I plugged in 1 watt amp and immediately came to this page. The lower half of the page has a very simple 1 watt amp you can build. Alternately, you can go to a manufacturer's website, such as National Semiconductor, the main manufacturer of the LM386, and look for battery powered audio amplifier chips. On the page for the individual chips, they will have data sheets with general diagrams on how to hook them up.

Remember, the more power you push to the speakers, the more battery power you'll need. With your description  of a typical day's use, you will be needing some seriously healthy batteries. 9V transistor batteries (small, rectangular 9V batteries used in smoke alarms) won't last very long.

Good luck with your build,
Qa
NachoMahma6 years ago
LM386 schematics are all over the 'Net. Google is your friend.
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> I also would need right/left balance
> If it will be better to use two of these amps
.  The 386 is a mono amp. For stereo, you must have two of them.
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.  You're not going to get a lot of bass out of a 1/8W amp, no matter what you do. The easiest way to "boost" the bass is to attenuate the treble on the amp input (see audio filter, audio attenuator, &c).
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.  What do you mean by multiple outs? If you are trying to drive more speakers, keep in mind that the 1/8W will just get divided up among the speakers - no increase in volume - and you may dip below the 386's output impedance.
hondasvx (author)  NachoMahma6 years ago
Ok I was not sure if the 386 was mono only or not. What I am trying to do in basic terms is make a four speaker camping stereo with some cheap outdoor speakers from best buy. I want the speakers to be amped so I can get more sound out of them than what a simple mp3 player will give me. The speakers have a 40 watt rms so I figured a small 386 will help boost them to drowned out other campsites and the river. If there is something better I can use I am completely open to anything you can suggest.
.  125mW would be OK for desktop speakers but it's just not enough power for an outdoor concert that you can hear over the river (why would you want to do that, anyway?). I'd go with 1W or more per speaker. If it's a big river, you may need more.
.  BTW power-to-loudness is a logarithmic relationship - it takes ten times the power to make twice as much noise. Eg, to be twice as loud as the 386's 125mW would require 1.25W. To be twice as loud as my 1W recommendation would require 10W.
hondasvx (author)  NachoMahma6 years ago
the basic reason is we float down this river in MO on these huge rafts. The day is basically a huge party day with tons of other people on the river as well. So I tried some small mp3 speakers this summer that were not powered off of anything but the mp3 player. So I am now hoping to build a system that pushes more sound out of the speakers to take on the rafts and use at our camp site. It will not be a concert and I know it will not complete drown out the river but loud enough to hear over the river and our talking. I will also use the system on my apartment deck and by a pool from time to time.

My conclusion so far from these posts though is it might be better to start off of an old set of computer speakers that are amped. This will give me stereo sound and a volume control system built in.
framistan6 years ago
The wattage of a speaker and an amplifier dont have to be matched up EXACTLY... but it is a good idea to have them somewhat close. If you try to drive a BIG speaker with a small amplifier it will not have good sound.. (no bass). If you do the OPPOSITE... drive a tiny speaker with a large amplifier, then it will easily blow the speaker pretty quick when you turn up the loudness. If you wire speakers in PARALLEL... their total resistance goes down... down.. lower and lower each time you add a speaker. This too will blow your amp. (transistor-type amplifiers do not like to have their output SHORTED or very-low-ohms.) Old style TUBE amplifiers are the opposite. They will burn out the FINAL amplifier tube if the outputs are OPEN (disconnected).
orksecurity6 years ago
What do you mean by "multiple outs"? What are you trying to drive?