We are all makers
MonoBox is a small, inexpensive powered speaker that amplifies the output of your headphone music player. It’s little but it’s loud! All the circuit parts are available from RadioShack. The speaker and cabinet are left to your preference.
You’ll learn how to assemble and solder an audio power amplifier using an integrated circuit (IC) chip, and how to choose a speaker and install it in a cabinet with the amplifier.
The core of MonoBox is a compact and efficient audio amplifier based on the LM386 power amp chip. It will run on 200mA of current using power supplies from 6V–15V DC. This gives you the flexibility to power it from a wall adapter, a 9V battery, or a car accessory outlet.
You’re probably thinking, “Sure, but it’s so small. Does it rock?” Fair question. The prototype has been exhaustively tested and it does indeed rock. Maximum volume output is 90dB, and with the added bass boost your socks will be rocked clean off!
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To power the speaker you could also have a solar panel on top so during the day you can switch from battery power to solar power by just adding a switch.
Found the diagram in the PDF.
this wouldn’t work in britain would it. any suggestions on how to make it work. also dont know where id get the components
No reason it wouldnt except youd need an adapter for the power brick (one of those travel adapters). Should be an electronics shoppe or order off the web.
hi saulx350z, the diagram is one Page 2 of the project: http://makeprojects.com/Project/MonoBox+Powered+Speaker/2396/2 – it’s Step 15, or, if you can’t see that for some reason, here is the image: http://guide-images.makeprojects.org/igi/X3WB2Tny1O2xSlQb.large – hope this is what you were looking for.
Volume: I measured peaks 90dbs at 1 meter distance before distortion set in. This was with an 8 Ohm speaker of mid/high efficiency. Not enough to throw a disco party but way above a typical computer speaker. I recommend a wall-wart power supply rather than a 9V battery for extended high volumes. Uses a lot of current.
It depends on the speaker. A larger speaker may have reduced high frequency response unless it’s designed as a full-range driver. If you’re unsure I’d say build the amp circuit alone and try it with that speaker mounted on cardboard as described in the article. if you don’t like it you can change to a different speaker for the final assembly.
I wish I could give a full answer. Do you mean it plays at low levels but stops completely when the volume is turned up?
Note that a number of the Radio Shack parts like the circuit board and some of the resistors come 2 or more to a pack so you won’t have to duplicate the whole list when making 2 amps.
Also, I guess I would also need to adapt the power for Australian sockets.
*Complete Battery Overkill*
Also, I guess I would also need to adapt the power for Australian sockets. Hmm…..
Stereo is covered at the end of the article. The LM386 amp chip has only one channel of amplification. The easiest way to go stereo is to build two of them. You have to make a small modification to the circuit at the input jack because the stock mono circuit connects right and left together. You would want one built with only the right channel connected and the other built with the left connected. Option: install a switch at the jack so you could switch to mono operation by connecting in the other unused channel.
I went into radio shack today and they had no problem helping me find all the items on the list. I’m going to build this over the next couple days. I found this on flipboard and thought it sounded too awesome not to try… I have never done a project like this, but your instructions appear well done. I will post on the outcome when I am done. Thanks for sharing this project.
My project is a sucsess, my amp is working well, and is really cool!!! Much thanks to the author for sharing these awesome and easy to follow plans!!!
Note from the author here. I’m abruptly out of the country for work and have unreliable internet. Apologies for the lack of replies. I will read all responses and answer as soon as I’ve sorted out certain industrial laser issues and made my back north of the border. Thanks. Ross Hershberger
so, when i plug in my amp via 9V battery or the enercell adapter 9V(dc) it makes a popping noise.. can anyone explaing that? regards, ryan
That is simply a small burst of electricity moving through the speaker, and causing it to ‘work’. Like when you play music, but instead of a controlled signal it is just an uncontrolled current.
Looks like I’m going to answer my own posting: The author clearly intended to indicate by use of a triangular symbol that the LM 386 is the IC in the circuit. However, by adding the + and – signs to the input leads, he created the symbol of an op amp. This is a mistake that only a person with limited electronic knowledge would notice, since the square wave output of an op amp makes it clearly unusable as an audio amplifier.
I think you are incorrect, in that there should be + and – terminals on the schematic symbol
Hauke, you need a log (audio) pot for audio signals. I don’t what exactly would be best for this circuit, but it seems that values between 10k and 50k are most common these days, though I’ve seen some amps that use 100k pots.
That is very nice! I like how the lion artwork surrounds the speaker, looks great!
Tim – Vocals are normally in the centre of a stereo recording. This means that they are present in exact same amounts on the left and right channels. Instruments tend to be placed more on one side than the other.
When making a mono speaker like this, the left and right signals get summed together. However, if at some stage during the construction, the polarity of either the left or the right channels is inverted, then anything in the centre, like the vocals, will get lost. This is because the vocals are now present as exact opposite signals on the left and right, and perfectly cancel out when summed.
This phenomenon doesn’t affect the instrumentation as they tend to be in different amounts on the left and right, and so do not cancel out when one side is subtracted from the other.
I can’t help you with regards the specifics of the circuit (I haven’t looked in detail at it yet), but a good place to start would be to look at the wiring of sockets and jacks – have you swapped a shield and a tip, for example?
setup would be the same
yes it would be capable powering a bit more powerful driver, but don’t expect much because its only 1W
very nicely done :)
distortion is boosted by increasing gain?
i made a stereo version because i had enough parts left: https://www.dropbox.com/s/fqv7p5zpogspep2/lm386-stereo.jpg
Is there a schematic for the stero circui? I built the mono curcuit and am building a second but I dont know how to connect the two for stereo.
build two circuits. stereo line in has ground, right and left channel. use ground for both and left for one circuit and right for the other. the original version has left and right together in one circuit.
Awesome. Worked great. My only issue is that the volume is half as loud in one speaker. I swapped speakers ad determined it is the circuit. Any immediate ideas. I’m assuming it is my craftsmanship to blame. I’ll probably have to make a new circuit.
Really want to build a stereo Do this :
Make 2 monoboxes In each, connect only one channel (left or right) of the input jack directly to the amplifier circuit board, and use a SPST switch to connect or disconnect the other channel, so each box has its own mono (or 1-channel) selector switch.
Set both boxes to 1-channel, then use a stereo headphone splitter to connect both MonoBoxes to your music player.
(I got this from the down of the article!)
i was wondering if you could get a picture of this im starting out in electronics and such and i was wondering if you could upload a diagram on how to make the mono amp into a stero amp.
Very nice! The pot is a great addition. I’m thinking of doing another some day with an option for line in level sources with a volume control.
That’s interesting – thanks for sharing. I might try the 1 watt chip on my next build.
Check your email inbox.
I would say check that there is no short and make sure the chip is not in upside down
yes
I’ve checked with Parts Express and they have the $0.98 oval speaker tha twe used in some of the prototypes still in stock.
Capacitor voltages are not critical, as long as they are at least 50% higher than the power supply that you’re using.
The bass boost in the circuit can exceed the voltage swing capability of the amplifier. If you get distortion on bassy music consider using the EQ on your music player to turn the bass down. Or refer to the article and disable/remove the bass boost parts.
We found in testing that some portable headphone players delivered a lot of noise when loaded with a high impedance. They need a lot of current drawn to shunt out and damp the high frequency hash in particular. That’s why the 100 Ohm input resistor. Terminating the headphone output with a higher resistance will result in higher noise on some source devices.
Builder’s issues solved via email. He built it right, but had the worng IC chip. See his further comments below.
can you help me?
I soldered, drilled the box, and the whole nine yards. I finally hooked up the power to see if it works but there is no audio. All I’m getting is a little bit of noise when I hook the power chord into the power jack. Ask me questions about the problem so I could give more detail and so I can get this awesome project to work.
I’m having the same problem. I’ve double checked all my work but everything looks like it’s in place. The IC chip I bought the LM386N from radio shack. I don’t know if that might be a problem.
Your IC might be upside down. (I think.)
I think its very helpful for me .
I want to have the option of my box being powered by a battery(in the box) and a wall plug. I know i’ve seen the instructuions here somewhere. can someone point me in the right direction?
I actually did this with mine. I just with a simple solution of soldering a 9V adapter to the same positive and negative power leads on the power jack. This resulted in being able to use the power supply not only for a source of power but also for a charger for my rechargeable 9V battery. If you want to do this I would also recommend adding a power switch to the system so that it will charge better, instead of the amp chip using current sitting idle. You end up with a nice rechargeable amp that you can take anywhere. this is the link for the rechargeable battery I have: http://www.ebay.com/itm/New-9V-280mAh-Ni-MH-PP3-Rechargeable-Battery-/310406636702?pt=US_Rechargeable_Batteries&hash=item4845ad649e
Awesome guide! I’m using a Nightfire Electronics LM386 kit I bought for $10 from Amazon. Saved me a little trouble assembling all the components. One comment on the circuit: looks like you bridged the input signals without resistors. I’ve read that this causes distortion and can even damage the source, because the two signals are essentially fighting to set “their” voltage on the same wire. It’s a good idea to run each signal through a 10k resistor before connecting them. But it seems that lots of people are following these instructions with no complaints, so maybe it’s not that important?
i did it. Awesome. powerful
Where Can I add a pot so I can have volume control?
Can you just use the volume control on your mp3 player?
Ad pot at audio line in.
I had a great time building this. Great project for an amateur. My radio shack was sold out of the 8 pin connector so I used a 14 pin instead. Same cost, I just had to be careful what I plugged into and soldered. I used a speaker driver scavenged from an old Samsung surround sound. The speaker was flush with the face of the box so I used the metal lid from a canning jar with fabric glued in to finish it out.
Is it necessary to use an ic pc board? Reply!
Can this be modified to make a preamp and drive an amp instead? How hard would that be?
Hi in the schematic there are two triangles pointing down so, i am a newbie to this and schematics. so can you help me?
Those two arrows are ground connections.
Thanks bonsai171, But there is only one positive connection.
Ground is negative
But there are 2 ground connections and 1 positive connections.Right?
I made a veroboard layout:
http://2.bp.blogspot.com/-NnoOf5NSBOU/UXzBR6jy68I/AAAAAAAAAVQ/-4bTuU2QCM4/s1600/MAKE+Monobox+(2).jpg
my build:
http://levysounddesign.blogspot.com.au/2013/04/make-monobox-trash-speaker.html
Thanks bonsai171, But there is only one positive connection.
Hey, Ross there are 5 caps in the photos but in schematic there are 4 caps. But how?
Two of the caps “stack” together to get a higher value.
Thanks, Pete that helped a lot.
I found an electronic crossover PCB via ebay in china…And I’m using a pair
of aluminum 2 way speakers; each speaker has it’s own amp. Power is a bit
funky. 2 18650 lithium batteries for the power, plus 2 14500 LBatteries for the
negative supply of the Xover.
Is it necessary to use an ic pc board?
No… but it’s a whole lot easier. I used to build prototype cameras @Polaroid. Once we
got BOARDS, they worked a lot better than the WWrap or P2Point vector boards we originally
modeled the circuits with. 2 boards for $13.00…
This is a cool project. I actually used a circuit similar to this to build a guitar amplifier into a cigar box (same workhorse LM386 and all). Only difference is that you would use a pot to control the gain. For any guitar players out there, you can very easily modify this exact same build (just sub out a couple of parts) to get a sweet-looking portable guitar amp. The following link shows the schematic (though it’s not my site or my work).
https://lh3.googleusercontent.com/-X8sUApMtOhM/UNEB4o8zwOI/AAAAAAAAArY/oQHvUsvDA2U/w500/amp-diagram.png
What speaker do you use? In terms of specs what works best for guitar?
Is there any more information on this, or just the picture? I wasn’t sure about a few of the connections as well- specifically, if the wires were crossing over each other or actually connected in and around the chip socket. Thanks.
There is an instructable for the Little Gem at http://www.instructables.com/id/The-Little-Gem-Mini-Amplifier-Guitar-Amp-/. Between their schematic, and the image I posted above, things should come together nicely.
The main difference between this schematic, and the one listed in this article, is that you have an extra potentiometer to control the gain (a must have with a guitar amp). I generally build my cigar box amps with a 1/4″ jack for a guitar input, and a 3.5mm jack for an iPod input. It’s nice to have something that you can play anything on. I’ve built about a dozen of these things, and I can’t say enough about them. This entire project can be assembled from RadioShack components for around $30-$35. I’ve also used allelectronics.com in the past in order to source cheaper parts (including a speaker).
For my speaker, I went a little overkill and used a ~40-50 watt rated mid-range woofer. I was able to find one of these for about $5 (though allelectronics is listing something similar at $9 http://www.allelectronics.com/make-a-store/item/GW-2048/4-40W-SHIELDED-WOOFER-8-OHM/1.html). This is a much better speaker than you need in order to build out the project, but I liked my speaker so much that I ended up putting the same speaker into all of my designs.
Please let me know if you have any questions!
-T
I used a pvc pipe to house everything! its great
Can i use a 4 0hm 100watt speaker driver? Will it run on a 9 volt battery ?