# Car stereo and Portable experts, help me build a DIY boombox.



## bundee1

There is a scene in Ghost Dog where he has a homemade boombox. It has 2 car speakers, a car amp, and a car stereo/cd head unit. I dont know what kind of power suppy it had. I was just at a BBQ and we wanted to listen to some music from our HD players but we couldnt get good sound out of the cassette adaptor and most boomboxes suck. Maybe for $250 we can build something that sounds good and looks better than a boombox with a cheap HD player through line out to amp to speakers type thing?

 I know people here know about car stereo installations and portable gear so maybe you guys can team up and help with this and maybe you can build one on your own for your next barbeque. 



 Source: What is the cheapest HD player with good battery life, and moddable hard drive capacity?$150

 Amp: I think for a boombox 40-60wpc will do the trick. Maybe a class D amp will run cooler and use less power? It should also have 2 sets of outputs (1 for maybe a subwoofer later)50

 Speaker drivers: I think speakers with clean treble, nice midrange and good bass are a must. Maybe we can keep them under $60

 Power Supply something rechargeable or battery powered is good. Maybe a Sealed Lead Acid Battery?

 Let me know all of your suggestions.


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## rickcr42

For best sound AND to keep it simple you want to use auto sound full range drivers rather than individual midwoofer/crossover/tweeter which would be a major undertaking to get right AND would mostly be power hungry.Do not use full range drivers meant for home use or they will most likely be damged from any direct sunlight or outdoor heat buildup.Car speakers are made the way they are for a reason-environmental extremes.

 Once you speaker requirements are nailed down I would look at trying to get around 10 watts clean which in reality is _very powerful _ in this context.The best way to go would be a chip amp and since _amp power _ is related _amp supply voltage_ steal a trick from car amplifiers and use two low watt amp chips in the bridge mode which doubles actual amplifier power output for the same amp voltage and would save on the powering voltage.Look for a design that will work at 5 watts and run of 9-12 volts with low current draw then bridge two and use D-Cells to power the box whic like in a real boom box give the longest amount of battery life though the louder you play it the faster the batteries will drain.Check National Semiconductor for the chip amps.

 I think the hard part here will be actual box construction.You want to minimize vibration from the speakers while holding down the weight PLUS it must not be sensitive to the environment (heat,sunlight,slight moisture).No easy task.

 the actual player can be anything,even a simple dock for jacking in whatever you have at the time as your source

 good luck with the project


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## bundee1

Thanks for pointing me in the right direction Rick. Ive never soldered before so Im a real DIY Noob. Im thinking wood/mdf/plywood for the enclosure. It doesnt have to look nice its just for backyards/bedrooms. Im thinking just a wooden box, some sort of cradle for the player and the 2 full range car drivers screwed into a wooden board that would then screw into the box. 

 How would I connect the chip amps to the power supply and player?


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## rickcr42

Quote:


 Im thinking wood/mdf/plywood for the enclosure. It doesnt have to look nice its just for backyards/bedrooms. Im thinking just a wooden box, some sort of cradle for the player and the 2 full range car drivers screwed into a wooden board that would then screw into the box. 
 

I personally would stay away from MDf in this case.that stuff weighs a damn ton man !You would need to put wheels on it just to move from point A to point B 
	

	
	
		
		

		
		
	


	




 If I could make a suggestion go with a dense plywood (as many layers as you can get locally) in 3/8 thickness.but a "half sheet" if your luber yard offers that option,some do in the funiture grade sheets (birch ply) and brace any panels internally that would have a tendency to flex.That is not just the speaker enclosure area but also the control area and any carrying handles.Simple "crap grade" pine is fine for this in say 1/2 inch thickness,3 inch width and cut into lengthwise braces.For an all purpose durable covering look to Tolex.the same stuff used on a guitar amp and not only will it take a flat out beatingf but comes in enough colors to satisfy most artisitic endevours www.tubesandmore.com is a good first source for a lot of the parts.

  Quote:


 How would I connect the chip amps to the power supply and player? 
 

Think "integrated amp" and design accordingly.the signal path should look like this :

 Opamp gain stage "preamp" to chip amp "power amp" stage.If the opamp is a cmoy type (high output current drive) you would add a DPDT switch to select where the output of this stage goes

 Ouput #1-Speakers
 Output #2- headphone jack

 the player would go to the preamp input which in turn goes to either headphones directly or on to the power amp stage for speaker use.

 Other things to consider are a tone control stage,system mute switch and possibly a simple rotary switch input selector and if you add switching phone jacks to the amp output you could even use the preamp and amp with other speakers with the jack switching off the internal speakers and then passing the amp output on to the jack for powering other speakers,maybe higher quality home speakers strictly for "in house" use or even with high efficiency speakers for gatherings and parties.would make the device much more multifunctional instead of locked into a single use.


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## rickcr42

This puppy looks pretty decent as a starting point.Check the bridge mode connection down at the bottom of the page 
	

	
	
		
		

		
		
	


	




http://www.national.com/ds.cgi/LM/LM384.pdf


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## ilikemonkeys

Hey buddy, 

 I had the same delima. I was goin gto a music festival and wanted to have some tunes for the campsite. I used a 2- dollar 12V tractor battery and the sonic T amp with a pair of Paradigm Titans. I just plugged in my Karma. It was unreal how much sound came out of the Titans. It was a great time!.

 I would highly suggest the T-Amp. I still have this thing hooked up to the battery and I've got about 100+ hours in it with almost no drain.

 Get some cheap micro bookshelves, a box, and you've got an awsome boombox for cheap!

 Good luck!

 BILL

 edit to add: I am in no way shape or form an expert.


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## dsavitsk

I second the T-Amp, though you can get a DIY version from http://www.41hz.com. It should be more efficient than the opamp based system, and thus not strain the battery as much.


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## bundee1

Rick how does that sound? Screw the t-amp to a board and mount the speakers to it. What kind of 12V battery did you use? Can you give me a link?


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## ilikemonkeys

i bought the cheapest car sized battery I could find at walmart. It was 20 bucks. 12V 275 amp lawn and tractor battery. Trickle chargers are cheap too, so I figure once this dies, I can charge if for a night and use it'll be charged for another 100 hours or so. I'm still on the same initial charge.

 I'd love to hear abou those 41Hz amps. Are they better than the T-amp? and are the compnents they send you any good? or would they have to be replaced too?

 whatever....

 B


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## rickcr42

You guys are not even close to a "Boom box" which I thought was the goal but more "portable system".Any car battery no matter how small is heavy and that right there takes it out of the realm of boom box which by the classic definition is something easily or maybe notr so easily but possbly carried from one point to another while playing.While I was thinking how to get there using D-Cells (as in any true boom box I have ever owned) which are readily available at any convenience,beach or camp store.

 Even a small weight gets heavy fast and a long truck down the boardwalk or to a campsite or the canoe with a 30 pound behemoth no joke (why all my coolers have wheels 
	

	
	
		
		

		
		
	


	




).The T-amp solution while a good one is more Stationary Battery Operated System than it is truly portable.

 If weight is then no consequence disregard the suggestion of 3/8 plywood and go straight up to a full 1/2 inch marine grade plywood.heavy but indestructable and with three coats of Marine spar Varnish damn near element proof (get the one with UV inhibitors).A couple of Pro Speaker Cabinet handles on the sides would also be a good idea for moving the beast.
 You also want to consider adding a tap to your motor vehicle battery recharging system and/or upping the current output of the alternator to handle charging two batteries (internal vehicle battery in parallel with the external amplifier battery) so when you drain the one in the amp you can plug it in to the vehicle and recharge it.


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## ilikemonkeys

inverters are real cheap too......and a great tool to have if a battery's gotta get charged.

 I'm with you on the D-cell battery solution to weight, but you'd need a lot to run an amp for a long time at listening level.......and if they run dry, you've got to shell out 20 bucks at the nearest gas station to replace them.....


 I'll bet you can get a small tractor battery or a sealed battery that would be equivalent in weight and output.


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## rickcr42

Quote:


 I'm with you on the D-cell battery solution to weight, but you'd need a lot to run an amp for a long time at listening level.......and if they run dry, you've got to shell out 20 bucks at the nearest gas station to replace them..... 
 

that is how it has always been done man.Load it,drain it,reload it 
	

	
	
		
		

		
		
	


	




 Until mine fell off a roof top and detonated on the ground I had to load it three times a week at a cost of $30 
	

	
	
		
		

		
		
	


	





 Not real comfy with a digital amp AND a switching supply in combination but for outdoor use maybe just fine.I always try to aim for the best solution within a price range if building something wanting to better what is commercially available or at least have features i find lacking on what is offered and a chip amp done right will compete with any mid level stereo even if that stero home based.
 Combined with a couple of full rangers and _maybe_ a supertweeter tacked on (piezo horn crossed in at around 12-15 khz with a simpe resistor filter) would go a long way towards true "high fidelity" while still remaining small and light with all the weight being the D-Cells.Still minor all things considered.

 12 D-Cells and a bridged amp which is how _all _ autosound systems do it to get high power from a limited voltage supply combined with a front end and tone controls I am thinking a "curb weight" of around 6.0 lbs with 4.0 lbs possible


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## ilikemonkeys

This is what we need to design.

 A vacuum tube amp boombox with a compact voigt tube and Fostex drivers. All connected to a Minimac with an external soundcard. all running off D-cell batteries.

 get on it.


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## rickcr42

Fostex drivers IS what I would use but ported.Tubes suck at these voltages unless there is more current available but no reason why pencil tubes could not be used if someone wanted to-maybe a hybrid tube/discrete the external soundcard is any USB DAC.

 I realise you were just being a wise guy but anything wanting to be done can be if you plan accordingly and pay attention to what is available.There really is no limit other than cost and/or skill level to what can be made.

 Full blown tube gear in a portable ? time to brush up on you voltage multiplier skills and look at Stve Benches web pages.old news man.


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## bundee1

Im just thinking of using this thing as a backyard boombox or beach unit. I could carry 20lbs a couple of hundred feet. I think the Sonic T-amp with a rechargeable 12V power supply would work. I would like to get 8hrs of use each time and get good non clipping sound out of them. 

 Anyone have a link for the battery?
 Is there a special cable I would need to hook up the batter to the amp?
 What car speakers would you recommend for this application?


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## ilikemonkeys

i like your thinking.....Go to Walmart > get eh cheapest car looking battery you can find. Mine was 20 bucks for a 12V 360 something amp tractor/lawn and garden battery.

 I've got the T-amp re packaged into a cogar box with RCA's and real banana plugs. Cigar boxes are great for electronics...cheap...wooden, and easily thrown away. 

 I unsoldered the original battery leads that fit on the T-amp PCB and hardwired a couple wires....nothing to difficult here..... then I taped them to the battery....I actually got the polarities wrong the first time (surprised I didn't fry anything0 but I got it right the second, and all was good in the land of tunes.

 I'm really listening to this battery on it's initial cahrge for over 100 hours at loud levels pushing big speakers.

 Go for it bro.

 Let me know if you have any questions ok?

 BILL

 Here's my rig....out at Clinton Lake in Lawrence, KS. It's still going strong!


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## bundee1

Doesnt putting a battery on the ground drain it quicker? 
 Gulp I dont know how to solder. ill give soldering a shot later. 
 So can I cut off the wires that go to the power supply and connect those to the battery directly?

 Can you post some close ups please? Thanks a bunch!

 To make it more portable would one of those big flashlight batteries work. I mean the really big ones.


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## ilikemonkeys

battery on the ground? No, no effect on the battery.....that I know of?

 Learn how to solder.....I did and I'm a microbiologist. Anyone can do it!

 don't be scared...it's a 20 dollar amp, and you dont even have to take it out of the origianl case if you dont want to.

 Everything about this amp makes total sense. There's a circuit board with a bunch of wires coming off it.....make sure that you attach the power wires to the battery, the source wires to the source and the speaker wires to the speakers.

 You're golden!


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## mono

The SI T-Amp is a good idea for maximizing battery life, and IMO, sounds great for what it is, but filling large areas with sound it will be a little shy on wattage- you'd also want the most efficient speakers you can find.

 As for integrated chip amp route, often at online surplus 'sites you can get more chip for the buck than going through digikey/etc. examples 

 You don't really need a 300A lawn SLA battery if you want it more lightweight/portable. The target voltage should still be around 12V, the SI T-amp would run off of 8 x alkaline or NiMH D-Cells, or pick-your-favorite size of small SLA battery like those used in computer UPS, like an 7, 12, 14, etc, AH cell. It's all a matter of runtime. Figure for 250mAH for the T-amp (depends on volume of course but ballpark conservatively high figure), you would get a pretty long runtime off of a fairly portable battery(s) size. The original AA cells a T-Amp uses are a bit too little though, runtime limited more but also the AA cells limit peak current potential more.

 If you want 40-60Wpc, you dont' want the SI t-amp. The 41hz kits are a better option then. Considering the project I'd not be as concerned about their parts in the kit, ultimately the drivers you choose are the bigger limit but as rickdr42 mentioned, auto speakers are more durable for outdoor use.


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## bundee1

I was thinking 8 rechargeable D cells. I would have to build an enclosure though. I think the 10 watts the T-Amp provides should be loud enough for a 10 ft radius.


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## bundee1

http://www.partsexpress.com/pe/showd...number=140-244

 Will something like this do to power the T-Amp? 

 How about these speakers?

http://www.partsexpress.com/pe/showd...number=265-372

 Last but not least how about getting 3 of these:

http://www.ikea.com/webapp/wcs/store...ts=10104*13805

 1 for each speaker and 1 for the amp and player. I would buy extra parts to seal up the bottom. and mount the speakers in a hole in the top. 

 Im sorry Im so needy.


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## ilikemonkeys

best buy.com has some cheap drivers for sale right now.

 If I were you, I'd forgo building a box unless you're quite skilled at building enclosures. 

 Buy a pair of paradigm Atoms and attach a bracket on their sides to attach them to the box that holds the batteries and the source. This way they can be removed and placed at a distance from each other.....they can be had for about 60 bucks a pair used.....


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## bundee1

you are right monkeyman, Im getting ridiculous. Thanks for the advice, Im going to check ebay for some paradigm micros or something small.


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## ilikemonkeys

man, I've used this combo for a long time now, and I dont think it can be improved on, unless you want to build an amp....which is fun, but can get really really out of hand.

 what about something like this?


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## mono

Quote:


  Originally Posted by *bundee1* 
_http://www.partsexpress.com/pe/showd...number=140-244

 Will something like this do to power the T-Amp? 

 How about these speakers?

http://www.partsexpress.com/pe/showd...number=265-372

 Last but not least how about getting 3 of these:

http://www.ikea.com/webapp/wcs/store...ts=10104*13805

 1 for each speaker and 1 for the amp and player. I would buy extra parts to seal up the bottom. and mount the speakers in a hole in the top. 

 Im sorry Im so needy._

 

I don't know exactly HOW portable you need this and it's not my build, but if it were I'd use bigger than 5" speakers.

 The batteries you linked are the old low-capacity type. Probably not any better than good name-brand AA NiMH. I would just use AA NiMH via the T-Amp's integral battery holder before using those. Besides that, at 8-10X of them, that's a lot of $ for a mere 2000mAH. You might find a 7000mAH (7AH) SLA 12V for about $10 online + S/H If you still want to go with rechargeable D cells, look for the higher capacity true-D sized NiMH. They're in the neighborhood of 4000-7000 mAH rather than 2000. Try to avoid off-brands as there are a lot of questionable ratings on D cells, instead try known battery brands and be sure it's the 4000+ range cells or you're probably just getting a cheap C cell in a D sized container.

 Had you considered getting a small subwoofer box? If you got one uncut you'd have more flexibility in mounting.


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## bundee1

I was thinking about using a sub enclosure. but wasnt sure I could get 10" drivers cheap. Would the t amp be able to drive them? Thanks for all your patience guys, I see things developing. Thanks!


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## cmirza

I dont know if you've seen this link:
http://talkgarden.tripod.com/sonic_impact_5066.htm

 This guy shows how he transfered his T-Amp into a Hammond enclosure with a SLA battery and charger. I've been wanting to do something like this (sans SLA battery and in a smaller enclosure), but need to get some soldering tools (and skills 
	

	
	
		
		

		
		
	


	




). You might find it handy as you proceed through your project.


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## mono

Quote:


  Originally Posted by *bundee1* 
_I was thinking about using a sub enclosure. but wasnt sure I could get 10" drivers cheap. Would the t amp be able to drive them? Thanks for all your patience guys, I see things developing. Thanks!_

 

Yes a 10" speaker will work if it has suitable efficiency. 10" might be good for your goal, though I might look for 8" because even though the weight "might" still be manageable, the overall box size is still typically larger.


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## bundee1

Alright guys Im halfway there. I just paid $40 shipped for the following:

 1) Sonic Impact portable T amps:
 1) Walmart 3-12 vdc (1000mA) power adaptor
 2) Batterymart 12V-7AH SLA batteries w/charger and cables

 Now Im looking at some Polk Audio RT15 for hopefully $40 on Ebay. 

 The last thing I would need would be a case or crate to put it all together and transport. 
 I was thinking of a rectangular crate I could line with felt to put the speakers in(facing out) and the battery and amp. I would screw a handle in to the top to transport it all like a boombox. 
 Thanks for all you help guys and if you have any ideas for something to hold it all please submit them.


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