[Ole Wolf] wrote in to tell us about a project he has been working on for several years now. The Wacken Death Box serves as a reminder that once you start a DIY project, it’s probably a good idea to finish it in a reasonable amount of time, lest it risk becoming obsolete.
His Death Box is an MP3 player that he takes along on his annual trip to the Wacken Open Air Festival. His goal was to construct a portable amplified music player that could be powered from either a car battery or charger. A Via EPIA Mini-ITX computer serves as the brains of the device, blaring his tunes from a set of car loudspeakers via a two-channel 100W amp.
[Ole Wolf] used the music player for a few years, improving it as he went along. He does admit however, that with the continually dropping prices of MP3 players, he decided to bring a small portable unit along with him to the 2010 festival, leaving his box at home.
Given the fact that far smaller and more portable devices make his music box seem clunky and obsolete in comparison, you might ask why he even keeps it around. We think that every hack has its place, and while you won’t be strapping the Death Box on your back for your morning jog, it fits quite well in a variety of situations. This rugged music box would be an appropriate choice to use in your workshop, at the beach, or even on a construction job site – places where you might not want to use your comparatively fragile iDevice.
This is so over powered for an MP3 player it isn’t funny. A beagle board would offer a lower power solution but would lack an HD driver. You could also gut an NSLU and use that with a USB sound device.
To cut the weight you could replace the wood with Aluminum and pop rivet it together. Another option would be to buy an old ammo can and use that as the case. You could also make it very water proof that way.
Maybe add wifi and or bluetooth and write some custom control software for Android?
As is it is a really powerful device with a lot of potential.
The title: “DIY MP3 player shows that no hack is ever obsolete”
The first paragraph: “The Wacken Death Box serves as a reminder that once you start a DIY project, it’s probably a good idea to finish it in a reasonable amount of time, lest it risk becoming obsolete.”
Wait, what?
“the continually dropping prices of MP3 players” then “places where you might not want to use your comparatively fragile iDevice” that’s quite dumb… this iThings never get cheaper.
Purduecer I am guessing he means that you should finish projects quickly or they could be come obsolete, but this guy got lucky that his is still usable?
That is my best guess.
ghetto at its best
:) I have a similar project using a beheaded laptop.
The starting idea was probably to build his own Gandalf-five-thousand-watt bass machine for Wacken Open Air. As seen in the film Lord Of The Weed, a nice new synchronisation for Lord Of The Rings.
This just needs refinement:
– Keep the speakers and the 12v car battery source
– Drop the “PC”, and stick with the MP3 player.
– Make the external buttons conform to the iPod remote specification (or whatever MP3 player is used).
– Provide a dock for said MP3 player.
– Add a 12v round car plug
– Add a charger circuit for the MP3 player dock
High powered “transportable” speakers are expensive and there isn’t a lot of choice around.
I’d lose the car battery thing, and just go with a $3 plastic 8xAA battery holder (but note 8 AA = 10V. If you’re using rechargables you’d want two 5xAA battery all wired in series to get 12.5v… but NEVER put standard batteries in or you’ll probably fry something with 15v)
@Scott,
You probably won’t fry anything with 15V for a system designed around a 12V car system. They (cars) output 14.4V from the charging circuit and most amplifiers work well within a range of input voltages.
Besides, running a 100W amplifier off of AA batteries will probably run the juice out pretty quickly, if they can even supply enough current to work at all. D size batteries would be a better choice for high power audio output.
@JamieWho – I thought automotive systems regulated to 12V, regardless of alternator output (~14.4v, as you say.. I have not messed with this at all).
I am still pretty confident rechargable AA’s could power the speakers and maintain a trickle charge to the presumed iPod.
I’m still new to some of this, but I think AA would suffice.
100W @ 12v is 8.3 amps. Assuming max power is unrealistic, since most amps suffer from distortion levels before they even get to 50%. So let’s say 4Ah.
The Eneloops are rated (and consumer tested to) ~2,000 mili-amp hours. Times 10 (to provide necessary ~12v) that is 20Ah, no?
Constructive feedback welcome.. I’m doing my homework, but some things I’m still not sure of. :-)
This device could easily access / be accessed from a network; thus it can play files that you store on your desktop machine.
It can also play other types of audio file, such as flac.
These two options make it a useful hack, even if it’s not what it was originally designed for.
If he’s going to be taking that thing to the Wacken festival, he’s gonna need to paint it black and cover it in spikes.
@abobymouse – many devices play FLAC now, if you install Roxbox (have it on my 2nd gen iPod nano).
@Scott
When you connect cells in series to make a battery with a higher voltage, the Ah rating stays the same. When you connect them in parallel, the voltage stays the same, and the Ah rating increases. The Wh rating stays the same either way.
For 1.2V, 2000mAh NiMH cells:
10 cells in series makes a 12V, 2Ah battery (12V * 2Ah = 24Wh)
10 cells in parallel makes a 1.2V, 20Ah battery (1.2V * 20Ah = 24Wh)
Ah ratings are usually given for a specific discharge current, or a specific discharge time period. Sanyo helpfully provides a graph with discharge curves at different currents for their eneloop cells http://www.eneloop.info/home/performance-details/discharge-current.html
Let’s say the amplifier applies a constant 50W load to your 10 cell, 12V battery. This means that each cell will be under a 4.17A drain. Looking at the discharge graph, you probably will get reasonable performance from the battery in that it will provide close to its rated energy output, but its only going to last for 30 minutes (24Wh / 50W = 0.48h) since the cell just doesn’t store that much energy.
Flac, yes! Take no flak from defective files. There is room for even wav files, and don’t forget high def sounds. Without Rockbox an i-anything is near useless.
The two speakers crammed into the tiny box would sound better in the combined bigger box. The speaker hookup is very klutzy, and not even needed. A electric bike battery built into a integrated box, tuned bass etc with computer, class D power amp….
Google what happened to jam boxes. Everything including sound has shrunk up to near nothing. We need jam boxes that kick ass.
@Ben
Thank you for taking the time to clear that up for me. Much appreciated!
Obviously I don’t completely understand some aspects. I’ve been substituting some battery packs with homemade Eneloop + battery holders from fleabay. Easy to replace low draw ~5v and 9v battery packs.
I will actually have to try this – I have a mass of Eneloops, a spare car amplifier, and a subwoofer and speakers doing absolutely nothing.
Does an amplifier typically have steady power requirements, or does that flux with music levels? Trying to understand if a 100W amp at 50% volume/power is really pulling steady 50W, or just peaking to 50W with a normal draw that’s much less.
@Scott
I don’t understand it too well myself, but yes, the power used by an audio amplifier is constantly varying with the music.
There are so many variables in the system that I wouldn’t try to pick a battery for an audio system based on theory and calculations. I would want to actually measure runtime using a test battery with a known capacity, using some average music at a comfortable volume level. You’ll probably find that the 10 eneloops powering a 100W amp last a good deal longer than 30 minutes when the volume is at a comfortable level.
Love it, got a set if JBL 6×9 car speakers that I wanted to so this with, nice work! Overkill, yep, but why? Simply because he could!
Overkill is great fun, I would like to see a v12 lawnmower next!
Car amplifiers that are made up of solid state transistors are still the best. ;
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