Instructables

Bringin' Back the Boombox!

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What happened to the good ole days of taking the boombox out and listening to music with your friends, family, coworkers or the neighborhood on a sunny day?  It's all been lost to the iPod generation.  Too many people plug into their mp3 players and by doing so shut the world out.  They don't share their music and the world can't share music with them.  What a terribly antisocial platform!  It's time to bring back the social side of music!  Unfortunately the classic ghettoblasters are all gone, but you can follow this tutorial and build a no-frills, portable boombox that will play any 1/8inch stereo input (Walkman, CD or mp3 player).
 
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Step 1: Tools and Safety

charger.jpg
drillbits.jpg
Notice: This tutorial makes the assumption that you know how to safely use the power-tools and hand-tools listed below. Only use a tool if you can do so safely!

Notice: This tutorial requires you to do some simple soldering.


Safety goggles
Table saw
Band saw
Dremel
Dremel circle cutting attachment
Drill
Hammer
Wood awl
3/32 inch drill bit
1/8 inch drill bit
1/2 inch drill bit
2 or 3 bar clamps
Tape measure
Phillips head screw driver
Sand paper
12V trickle battery charger
Soldering iron
Solder
Helping hand (optional)
Wire Stripper
Crimping tool or pliers
Scissors
Permanent pen
Small flat-head screwdriver
Voltmeter (optional)

ben ehrlich3 years ago
could you use a 12 volt wall power adapter to power it?
tomorrow_today (author)  ben ehrlich3 years ago
You can. Make sure the 12V adapter's current rating is high enough for the amp.
i found a 12v adapter laying around that fit and plugged it an, nothing worked. Sorry im kind of a newb, but managed to build the thing, im just waiting on a charger to charge the battery...thats why im wondering, what form is current rating in, is it mA?
head to this website, its kinda the same thing and should have all the info you need
http://www.ehow.com/how_4448174_subwoofer-computer-home-theater-system.html
and how many mA's are required for this amp?
tomorrow_today (author)  ben ehrlich3 years ago
There is a symbol on the adapter that shows the polarity of the inside and outside of the plug. You want an adapter with the center positive. I have another 12V t-amp that is slightly smaller that requires a 2000mA (2A) adapter. I hooked up the amp6 to that adapter and it works fine. Just probably best not to crank it or make sure the adapter doesn't get to hot.
I was thinking of making a similar project, but have very limited knowledge with lead acid batteries.
All I know is you have to use the sealed lead acid deep cycle(leisure/golf cart) type.

As I heard when charging lead acid batteries that hydrogen gas can build up and it can be very dangerous in an enclosured area.

So preferably I guess It's wise to have a removable back to the boombox enclosure and take out the battery/batteries to charge them.
And I'd use a smart charger just to be safe.

Also when the amp is inside the enclosure, doesn't it overheat though?
As amps that I seen that are mounted inside wooden or plastic enclosures are usually the plate amp variety.
And have a heatsink and large metal plate on the outside back, sometimes with extra heatsink fins.

Anyway I like the construction of your box and the way you attached the battery.

I'd put a speaker protection module(to protect against switch on thumps, amp going DC,etc) in between the the amp and the speakers though like this one:
http://connexelectronic.com/product_info.php/products_id/71?osCsid=qcr5h8phhtp80kmusjq2s5a0q7


rug3 years ago
what is the make and name of that mp3 player ????
tomorrow_today (author)  rug3 years ago
It's a Cowon D2. I've had it for a few years and I love it.
thanks
ben ehrlich3 years ago
Ok, like I already said I am a complete newb, I got the amp6, not the basic, the one that comes already assembled. Anyway, I plugged everything in and nothing happened, so I looked on the 41hz website and it said i need to add a transformer 12 to 15 VAC or 16-20VDC. What does that mean? I know i got a part in the box the amp came in, I had no idea what it was so i put in in a drawer, do I need to solder this onto the amp or something like that?
tomorrow_today (author)  ben ehrlich3 years ago
I'm sorry, I don't know the answer to this. 41hz seems to have an active forum for the amp6.  You may be able to find an answer there. Best of luck!
Gammalf3 years ago
How long works the Battery whit full power?
tomorrow_today (author)  Gammalf3 years ago
I'm not sure, but I just spent a week working in a machine shop and was able to play it at maybe 3/4 power for 6 to 8 hours a day. I would imagine full power would last at least a couple hours.
CoolKoon3 years ago
It's quite a nice idea you have there! However there might be some aspects that could be improved further:
-I don't think keeping both speakers in the same box without any kind of separation is a good idea. They tend to cause interference with each other that'll worsen the sound quality
-The interior of the box could really use some dampening too, for the same reasons as above. Plus both sides of the speaker produce vibrations, but the reas one's phase is shifted by 180° i.e. inverted, so if such waves combine they'll cancel each other out.
-I've checked out the amplifier's and the speakers' specs and have to say that the speakers are an overkill for the amp. You see the speakers are WAY more capable than the amplifier is: they can do 50W RMS and up to 250W max (that is for music you'd be pretty safe even with a 150W amp), yet the amp is capable of only half the RMS value at most, 25W and only with 10% THD (amount of distortion, for music it's WAY too much). The maximum power for 0.1% THD or less (which is way more acceptable :P) is 15W, which isn't a lot. So if you're worried about battery life, you can keep your current amp. But if you want to get the maximum out of your box, you might want to consider getting a more powerful amp. A 150W one would do. Keep in mind however that you'd have to add at least another battery for increased voltage and even then they would be discharged pretty fast. Actually 4 batteries or a transformer would be preferred. You'd also have to insert a bigger heatsink. But still, it's up to you, as I said.
I strongly recommend you doing at least the first two things (separate the speakers and dampening). Good luck ;)
tomorrow_today (author)  CoolKoon3 years ago
Thank you for your suggestions.  When I paint it this summer, I will add a separator between the speakers and line it with a dampening material.

The technical details in the Amazon article are incorrect, these speakers are actually 35W rms and 180W instantaneous max.  They're still overkill, but I'd rather have it that way because I can safely crank my current amp all the way without worry of damaging the speakers.  At half volume the sound quality is pretty good and the volume good for comfortable outdoor listening.  At max it does distort heavily, but when I crank it up to max I'm not looking for fidelity anyway.
Sorry buddy, not quite so.

Its rather hard to kill speakers by putting to much music power through them, as its all AC and comes in peaks (which is how there is such a huge difference between rms and pmpo). but when your amp distorts, your chopping the curve of your wave out, flat-lining your signal, aka DC. the speaker stops moving, and so all the power your feeding the speaker goes as heat. which is baaaaaad, and kills speakers. its far easier to burn out big speakers with a small amp than burn small speakers with a big amp (although you can make them rip 'emselves to bits, which is fun).

the moral of the story is distortion is bad and not healthy for your kit, please don't do it.

*rant*
I personally believe that heavy musical distortion (obvious caveat for guitar distortion, which is similar but not the same) is a horrible, evil thing to do, especially in public. If I was Supreme Overlord of the Universe, I would make publicly playing distorted music punishable by perferation of the eardrum and bludgeoning the offender with the offending device until one of them is broken. in the case of a mobile phone, where perforation and boot assisted rectal insertation may be performed.
*/rant*

ahem. CoolKoon knows what I mean im sure.

if its not loud enough, get a bigger amp. personally, I'd go for about 50w turned down (less heat), using a pair of 'chip-amps', either as a kit or built 'dead bug' style, using 2 identical batteries for a +/- 12v supply, or 4 for a +/- 24v if you really wanna bust some serious noise.

If your not up for building the amp, id be looking around pawn shops and car wreckers for an old little car stereo amp, again about 50w. their not common any more as mosfets make most head units capable of this, but an old transistorised external one should be able to be found for pretty cheap.

all up, great idea, bring the beat back. theres a dude who wanders around my city listenin to reggae/dub thru a boombox (not to loud, with respect), and gets alot of props. Freo's a pretty cool city like that
CoolKoon arjo3 years ago
I definitely do :D

<rant>
There's something even worse that has began to take roots recently with the advent of phones with "stereo" speakers: ignorant kiddos (well, teenagers, but that doesn't make a difference) use their phones to conjure up some "background noise" while they're gathering in groups. Since the sound's actually devoid of bass, it's literally nothing more than some nasty background noise....
</rant>

I haven't thought about the distorted sound that way, but it actually makes sense. And you're right, burned wiring means you can pretty much throw out the speaker (although I've seen some recoil kits at my local audio store....).
I didn't want to bring up the PMPO issue because there doesn't seem to be a consent even amongst professionals whether the value's relevant, meaningful and comparable at all. But I still think that you might get away with a more powerful amplifier (>50W RMS) for this speaker, as long as you'll use it for music (where the output, amplitude and power in general is constantly changing, thus reducing the risk of overload).
As for the amp itself, if you're not afraid of using a soldering iron, you can buy some amp kits just about everywhere with all the necessary parts included. All you have to do is to solder everything together according to the instructions and take care of the power supply.
arjo CoolKoon3 years ago
yaha. thats why they get the special deluxe boot treatment. I wear size 12's. and I like hiking boots. with lots of knobbly bits. and buckles. how i long for sweet revenge. sigh. *inserts deep-ear-buds* huh, what?

anyway, back to the real world of getting some sweet, clean sounds over your shoulder so you can blast those lamers off their feet with your epic phat bass.

the biggest issue with PMPO is there is no standard, it isnt relevant to *anything*, its just a number (unless they tell you what signal they feed and how long it will last before death, and even then nobody else will use that signal and that period). RMS is very defined, so you cant get it wrong. how much power you can push through a speaker, at the real world cutting edge, is completely different depending on the source track. listening to lounge jazz will have a completley different fail point than listening to dubstep. go figure.






arjo arjo3 years ago
oh yeah, forgot to add,

If anybody out there is planning on going the DIY amp route for this project, remember a pretty significant cost saving can be had in the power supply department. The rail filter capacitors are one of the most expensive parts of an amp, along with the transistors and heatsink. they sit between the rectifier and the amplifier to smooth out the 100/120hz (twice the grid frequency, and very audible with undersized caps) ripple which is inevitable when using grid power. As this project is designed around a battery, which inherently supply pure DC. so no (or very much smaller) ripple caps are needed. 

at 10-30 AUD a piece, and typically 2 required (for a dual rail supply), Doing It Yourself and choosing to underrate these could make the project a whole lot cheaper. If thats your primary objective. of course, leaving them in wont hurt anything.

that said, car audio shops always have huge 1F caps for sale for attaching to subwoofer amps. I think this is to reduce the instantaneous current surge through the long power leads that typically run from the engine bay to the boot, which would decrease the volt drop and therefore improve peak maximum power from the amp. that's only a theoretical explanation tho, ive no experience in that field of toys.

amirite?
CoolKoon arjo3 years ago
Nah, I don't think them getting the boot treatment will force them out of their ignorance. Maybe they can hardly even tell the difference between regular music and the noise coming from their phone.....
Anyway I doubt you'll save much on "underrating" the  filter caps in the supply, besides if you go to the edge they won't filter out the mains hum and the amp'll pick it up. The biggest cost is always the transformer, the transistors (in case of a DIY amp) or the IC and the heatsink's probably the last. The filter caps are expensive only if you need them to handle higher voltages (over 20-30V I'd say), which is necessary only for more powerful amps (several hundred watts and over). But boviously this only applies if you have an AC power supply.
As for the 1F things, I think it improves the speaker's response for transients as well and probably acts as a PFC too, which improves the amp's efficiency. But I think it only makes a difference for really big speakers with a lot of power to dissipate and a lot of inductance to compensate for. And I don't think they're cheap either (I think I've seen them for >$70 a piece a few years ago).
arjo CoolKoon3 years ago
you cant force knowledge into their heads, no. but with perforated ear drums, they'll never need to know about sound ever again. problem solved. the boots just for my own satisfaction.

I'd dropped back into general theory, must admit id forgotten we're working with 12v here, which, yeh, makes things alot cheaper (seems caps are roughly logarithmic in voltage/price, gets ker-ching fast). using standard techniques, about 15w is as good as your gonna get from that voltage (its actually really good, had a quick read on the module and its a very nice performer), car amps have to pull all sorts of tricks with fancy power supplies to give em enough voltage to drive an 8ohm load at any significant power.

if your designing your own amp system, I always aim for the highest voltage I can feed it with, it just makes all sorts of things easier. most of the commercial amps ive seen run at about 60/70v, and ive built one that runs at 110v (no, no not mains, I was using the B+ transformer from a TV, so it was isolated and much safer. not that id have ever called it safe, and ended up dismantling due to saftey and performance concerns, fun for a fiddle tho)
CoolKoon arjo3 years ago
Commercial amps? At what power? AS I really doubt you'd need 60-70V for anything less than 500 W. And the 110V one......I presume that's a monster. Of course that sort of voltage can kill you several times over even with isolation. It's just you'll have less opportunity for getting electrocuted (i.e. touching the radiator for instance won't kill you :P). Why did you end up dismantling it? Too much distortion or what (it's not that such thing can't be made safe either)?
arjo CoolKoon3 years ago
nah, even some pretty small ones. an old tape machine with an internal amp i gutted had 45v +ve to -ve and it must have been pissy tiny. that was outta the mid 60's. Ive got a nice Hitachi amp block thats 75v, I think she does about 100w. my Pioneer 30w has 60v across the rails. just a trend ive noticed.

heh, yeah, that was a bit of a hack. I had a amp chip that was rated to 90v, and had the powersupply built for a beefy flyback driver and simply wanted to see what happened. if it didnt kill it i was going to use it for a sub driver (where everything would be inside one box). It kept its magic smoke, but acted pretty funky, unstable, and some strange artifacts on the scope. so it went straight in the bin. I dont advise playing around with this sort of thing.

The flyback driver is an inherently dangerous toy, so every tiny step you do is triple checked, and keep yourself well away from the guts when using or testing it. also, built to keep things safe (, plenty of heatshrink, care in cable routing, a discharge LED across every large cap, and a strict operation procedure. that said id never let anyone else use it. makes good, long PHAAT sparks tho :D, and id estimate (from what fuses dont blow) about 6-700w power draw (i dont really know, the ammeter goes all stupid when you strike an arc :D). Its vastly overtaxing the transformer and the whole switching stage get pretty warm fast, but its usually only used at a very low duty cycle (although it survived about a minute long arc once)

wow, im so far off topic here, sorry folks ;-)


CoolKoon arjo3 years ago
Holy crap! Maybe I should've asked for those amps' efficiency as well. Still, it VERY rare to see any chip that's rated for 90 V. Wasn't it by chance some unknown (possibly Chinese) brand? :P And I bet the chip wasn't brand new/"lighly used" either (which would explain the artifacts showing up on the scope), It was probably halfway to its failure (or failed already).

Up to this point I thought that flyback drivers have been used only in CRT devices in conjuction with a flyback transformer. Say, was the sparking part of the "normal" operation as well? But regardless of that I wouldn't put any measuring device near to a sparking equipment......are you sure you don't have something shorted in it? Oh and how much power does the thing give out actually? :P
arjo CoolKoon3 years ago
yeah it was a strange one, came from a bag of random electronic goodies at a hamfest. i normally would use closer the perscribed voltage, but the only other large transformer i had to hand was 24v, which seemed a bit pissweak considering its extreme rating so i went for broke. which it did. it was just labled with some numbers and came with a crookedly photocopied datasheet, so yeah, probably from some backwater far east factory, and had been sitting for quite a while.

yes, the sane engineering folk use the flyback for a good couple of things in a CRT, Horizontal scan drive, sometimes to get any other odd voltages the the rest of the circut might need (sometimes a 30 or 50v rail), and the grid/focus for the guns. its main job, is of course to provide the high voltage to slam electons into the phosphor of the tube to create the picture you see.

Less sane hacker folk like myself like the well constructed and potted high voltage transformer and integrated voltage tripler and use them to feed our insatiable lust for ozone and plasma. by winding your own primary on the exposed ferrite, you can define the transformer ratio. by running at a much higher frequency (although it does need to be tuned to a multiple of whatever it was designed for) you can put alot more current through the thing. I started playing round with making little drivers for car ignition coils and got used to short, fat, hot sparks, and was dissapointed by the longer, but very spindly arcs you got from running a flyback at 12v/24v.  at 110v, their much longer, fatter and hotter, and quite satisfactory. Ive not a clue how much power is actually in the arc... its not particularly efficient, I sort of wanted everything close to saturation, so the bipolar predrivers, drive transformer ferrite, power fets and flyback ferrite all get warm to hot, but you know, its designed to do a 10sec 1/4 mile, not get 25km/L.

possibly now your asking 'why'? cos it makes me grin and giggle like a madman :-D which is by far the best reason to make anything. and it didnt cost me a cent, 100% recycled or junkboxed which is a nice feather for the cap. I should probably write somthing up on it, but im not sure if its the thing for instructables.
CoolKoon arjo3 years ago
But what was the point in driving that thing to the edge if you were pretty sure it won't be able to handle it? In the way you've been describing it it's short of a miracle that it has managed to keep its "magic smoke" in :)
Say, are we still talking about your "nonstandard" amp here? Or was this flyback project something totally different? If so, did it have any practical use as well? Besides giving out loong sparks and getting everything hot fast due to saturation? :P
I'm sure it didn't cost you a penny to build it, since you've used salvaged parts. But still you spent some time on it. And since we know that time is money, I rather focus on things that are at least a bit practical (well, at least you can touch them or something). This is why I'd love to build a DIY plasma globe from some burnt-out bulbs and of course a flyback transformer (I'm already stacked with flyback transformers for this reason). I'm also planning on building a "real" plasma speaker as well (there's an instructable for that over here somewhere). Now the only things I need are time & patience. And a place to do the experiments, too :S
tomorrow_today (author)  arjo3 years ago
I'd like to say to all the audiophiles out there that are looking at my project in utter horror that this is a portable device developed by a person with limited time, knowledge and resources(aka money).  I built this thing and made decisions on the fly and very little was planned.  I chose the 41hz amp because it has very high fidelity at regular listening volumes.  It was my one splurge for the project.  I used the speakers because they were laying around collecting dust.  I built this boombox to share music with friends while we play disc golf or have lazy days in the park.  For these purposes, it works wonderfully.  It also has enough power behind it for a spontaneous party or gathering in need of a beat.

I understand your concerns CoolKoon and arjo.  I should have been clear earlier.  The "max" or "max volume" to me is a volume short of clipping.  When my player (volume from 0 to 50) is connected to the boombox, the "max" is about 40.  The distortion I'm speaking of is not clipping, it's a wavering of sound that I believe is due to the low mass of the box, resonance and the small distance between the speakers (9in).  I'm sure there is also some audible distortion from the amp at this level as it approaches it's maximum output, but that distortion is far outweighed by what I am hearing.

If I were to make a change to components, I would put in smaller, more efficient speakers that better match the amplifier.  Also, I don't want do anything to increase the weight because, as I said earlier, I like to carry this around while I play disc golf. The weight of the system right now is comfortable to carry through 18 holes and the walk home.

I encourage anyone considering building their own boombox to customize it to their needs.  Don't blindly follow what I've put in the tutorial.  Do some research and find the components that'll you'll be happy with!
Oh come on! If I'd be a *real* audiophile then I'd be complaining about the fact that you didn't use tubes to do the amplification (and spent a fortune on the tubes alone) :D
I just wanted to let you know that you didn't bring out the max from your speakers with that amp. As you've mentioned that you need to be able to comfortably carry the thing on the street and on the disc golf course, you'll have to stick to the current setup, which is fine. Engineering is always about making compromises all the time anyway. You have to sacrifice power for portability and so on. A single battery won't be enough for more anyway.
I'm not sure about the "wavering" you're talking about, but if it's present only at high volume (and the sound level at which this starts drops as the battery gets discharged) then I doubt it has anything to do with the resonance (which just worsens the sound quality) or low mass (that just gives you less surface to vibrate i.e. the boombox will be less loud). It's more likely that your battery just can't keep up with the power demands of the amp at some points. But this can also happen when run from the grid (I also encounter this problem when I turn up my speakers too high and the input's too loud as well). You see there's a thing called internal resistance. Unfortunately this "phenomenom" causes the supply voltage to drop as soon as you connect ANY load to the power supply (unlike the ideal power source whose voltage never drops and which doesn't exist). The more you increase the load, the more will the supply voltage drop (down to zero, when it's shorted). Now as your amp's power demand increases (and hence the supply voltage decreases) up to a certain point, its transistors will stop conducting (their gates/bases will be shut off). At this point the sound might become very faint or even muted completely. But as soon as the power demand decreases (you turn the volume down or the song comes to a more quiet part), the voltage rises back to an acceptable level again and the amp works again as expected. This can happen to an amp run on AC or DC as well. Actually the lower the battery's internal resistance the longer can you run a high-power gadget on it (the lower the voltage drop as you increase the load). Fortunately lead acid batteries have quite low internal resistance, therefore they are more suitable for such usage than Li-ion batteries for instance. Now I'm not sure whether I was clear enough on the concept. Be sure to ask if you don't understand something (and want me to go on :P).
heh, dont worry man, id hardly call myself an audiophile, *all* my kit is hodgepode hacked together crap. its just when you hit that upper edge of an amp, well, its like my brain trying to divide by zero, just cant be tolerated.

honestly im just trying to be as constructive as i can to this thread simply cos i think the concept is an epicly good one and something I want spawned as much as possible. I've recently been tweaking up a similar little setup using an amp chip ripped from a TV driving a pair of 6" clarions with a similar set of goals. needless to say, ive got alot to tell on the subject. I always figure the more info, the more ideas, the better your end product will be.

sounds like coolkoons partition idea would go a long way to solving that sort of artifact. it would increase the rigidity of the box and isolate the speakers from each other.

the last paragraph should be a sub conscious mantra to everyone who plays this game ;-)
BTW I also have some plans for making a similar speaker system. The design will be slightly different though (a 2.1 system with more powerful speakers and a woofer) so it won't be a boombox. But the concept of building a speaker system from car speakers is the same. It'll be finished as soon as I'll have the necessary resources (financial one and time :P) to finish it. In the meanwhile I've read up a bit on the speakers' ratings. Turns out the RMS wattage is determined by using a wave with a constant frequency of say 1 kHz (and constant amplitude as well). I'm not sure about the shape (probably sine or square, but most likely sine), but the thing is the RMS wattage is the power that the speaker can withstand at this frequency without destroying itself. Now the inst. max. is determined the same way, only the input is replaced with some "testing" music instead. No song has ever a constant amplitude nor a constant frequency, therefore a speaker can withstand more of this musical power, hence the higher number. This is why I said that you can get away with a much more powerful amplifier too. Maybe not 150W, but 100W might be fine (unless you want to use it for a guitar amp). The problem with car speakers is that they seem to be "overrated" (at least I've heard such rumors), so in reality they can't withstand the powers they're rated for without permanent damage. Still, more powerful amps tend to be either more expensive (the ICs) or have to be built by yourself (the ones with "plain" transistors) even with a custom-built power supply (do it only with EXTREME caution, as electrocution from that might result in death :P).
You've also mentioned that at max. the sound's heavily distorted. Well as for me I worry about fidelity no matter how loud it is (I really can't stand listening to heavily distorted music).
tonyt3rry3 years ago
Hi, I have been trying to find a amp in the Uk, I was wondering if you could possibly guide me to a amp in the uk that isnt exspensive but loud the speakers I dont think should be a problem for me
Try Maplins they stock decent mini amps and kits to build amps at a decent price.
tomorrow_today (author)  tonyt3rry3 years ago
I'm on the other side of the pond. So I'm not sure how much help I can be, but the amp that I use in this tutorial is made in and ships from Sweden.  Also, there is an audio parts supplier similar to Parts Express that is out of Germany called Intertechnik.  I hope this helps.
hanley3 years ago
 Hi. great idea!
How long does that type battery last when playing music?
Stealth0073 years ago
Here's and idea for a box.  Why not use a portable ice chest with or without wheels?  Certainly more attractive, not to mention cool.
resago3 years ago
The 80's called, they want there boombox back :)

DIY Dave4 years ago
where did you get the dremel hole cutter?
tomorrow_today (author)  DIY Dave4 years ago
I picked it up at Lowes or Menards. I don't remember which, but you can also purchase it on Amazon.
thanks
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