Welcome! Here is some information about my boombox project. The idea of building a portable soundsystem originated from the World Championships of Academic Kyykkä in 2007. There we (my Kyykkä team) came across many variations of DIY boomboxes... and we decided that we should have one of our own next year.
The project got wind under it wings January 2008 and after hard browsing through web we decided that Mikemons idea of the boombox was closest to ours so we copied the idea (big thanks to him). The boombox finished in time and was used in World Championships of Academic Kyykkä 2008. The developement of the boombox continues and I will be adding more info as it comes along.
Because this is a portable device, I chose a D-class amplifier kit called AMP6-basic. It's manufactured by the www.41hz.com and was easy to solder together. It delivers 2x25 watts (RMS) @ 4 ohms. It is based on the Tripath TA2020 chip and the best thing about it is that its efficiency is about 90% in spite of volume level. Price: 41 euros.
The case is a normal tool case made of aluminium. It's strong and light and you can also pull it behind you! Price 49,90e.
A sensitivity rating tells you how effectively a speaker converts power (watts) into volume (decibels). So in a project like this I recommend to use as sensitive speakers as possible. I chose Blaupunkt GTX-803 3-way car speakers. They have a sensitivity of 92dB and car speakers tolerate variable temperatures and humidity. Power-handling is 55W RMS / 240W MAX. Price: 49,90 euros.
Battery and charger
For power supply I ordered an ExtraCell 12 V / 12 Ah sealed lead-acid gel battery and a 12V / 600 mA charger. The size and weight of the battery (3 kilos) surprised me first but however it fits well in the case. Price: 56,30 euros.
For audio source I bought Clas Ohlson 2 Gb mp3-player with FM-radio and microphone. Price: 39,90 euros.
First construction day
First I needed room for the speakers, so I removed the original front panel and made a new one of water plywood (10 mm thick). I mounted it two centimeter deeper than the original was to retain enough room for the speakers and the grill.
Although the case was leaking I made the first tests with a laptop and an mp3-player.
I bought a steel grill, painted it black and attached it with rivets.
I applied some sealing compound on the edges of the front panel and sealing tape between the front and the rear part of the case. After that I made more tests. Disappointingly, the rear panel wasn't strong enough. It resonated on low frequencies so it needed to be stronger.
I laminated several fiberglass layers to the rear panel, which stopped the low freaquency resonating. I also added an on/off-switch, a power-on led and RCA-inputs. So now it’s ready for action!
World Championships of Academic Kyykkä 09.02.2008
First field test at World Championships of Academic Kyykkä proved that this boombox really works! It plays really loud and also cheers people up.
Total: ~260 €
Finished boombox weights about 13 kilos so it is not too light but when you pull it behind you, weight doesn't matter. Now you can build your own one!