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|2nd October 2009, 02:00 PM||#1|
Join Date: May 2004
My take on a Boombox / Boominator / Portable / Soundsystem (Completed with photos)
I was planning on building a failry large portable powered speaker system similar to the Boominator on another thread.
It was quickly getting big and expensive, I was going to use pa speakers and a class D amp.
I realised I had some car speakers and a small chip amp (Lm386 about 1/2 watt) lying around. So I put the speakers in a small cardboard box and fired them up. There was no bass but I realised I had the phase reversed on one speaker, once this was fixed it sounded good. 1/2 a watt was not really enough though.
I ordered one of these which is a chip amp based on the BA5406 cost of £10:
This gives about 2-3 watts a channel which was perfect for my requirements. The speakers are the front 4inch speakers from a BMW 5 series from the early 90s, they are 4ohm and give a nice full range sound and a surprising amount of bass!
So I designed a box in google sketchup, (I will post a pic soon, I'm on Linux at the moment so need to fire up windows to get a screen-shot)
The design was to use 12mm plywood, but I actually bought a sheet of 9mm so the dimensions will need adjusting if anyone decides to build one.
Here are the pics. (CLICK TO ENLARGE)
The amp is simply mounted by using long bolts and drilling holes in the wood which the bolts are then glued in.
Everything is glued with waterproof glue, my cutting was not very accurate but as long as you have a wood plane you can plane everything down to size, and then sand down for the final finish.
I finished the surfaces with Tung Oil, this is a natural oil from an edible nut. You apply a weak mix with white spirit and allow to dry then apply gradually more and more coats less and less diluted. It gives a really lovely finish and is water resistant. It is sometimes used on kitchen worktops.
The unit is powered by a battery from a model aeroplane, I have several of these. The ratings vary from 8.4 volts to 9.6 volts. The smallest one is a 600mah 8.4volt Nicad pack and will run the unit for about 5 hours at a medium volume or perhaps a bit more at low volume. So you get about 1hour per 100mah capacity. The smallest battery only weighs about 160grams. Although the whole unit seems to weigh a couple of kilos.
You could just buy 7 or 8 standard AA rechargeables and careful solder them together or put them in a battery holder (they are not designed to be soldered so you would have to be quick) and you would have a very good pack as most modern AA batteries have a capacity of around 2000mah so would run this thing for 20 hours!
The ipod is plugged straight into the inputs with no volume control. 2 different feedback resistors were included in the kit to adjust the sensitivity/gain. I deliberately kept the gain a bit low so that when the Ipod is at full volume there is no distortion.
I added an LED to indicate that the unit is on, its a standard one not a high brightness one as they use too much energy. I used a resistor to limit the current to about 5ma.
I tested the unit at a Psy Trance music festival and I found it fun to play 80s pop and 70s folk music at people as a complete alternative to what was being played around us!
Last edited by DunkH; 2nd October 2009 at 02:06 PM.
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