Thursday, June 7, 2012

DIY powerful, yet cheap mobile iPod speakers

When I first thought about this, I wanted something that would be cheap and fun to build. I came up with a LM386-based speaker, giving a good balance between weight and power. Using a shoebox as enclosure, the whole thing weighted under 500g, battery and speaker included, for less than 20€ ($25-28).
It was loud enough to use it indoors, but less effective outdoors. The sound quality wasn't perfect, but good enough to be "listenable". All of this was built last year...
First version... The case? A simple cardboard, wooden box, with lots of hot glue. The holes were "drilled" without any alignment...

Back of the "box"... A small perfboard holds the two LM386, half a watt each. Everything is powered by a 9V battery

In February, I thought about building something a stronger than cardboard, with a bit more power to give, while keeping it portable. 
First concern: what would I use as amplifier? I wanted to keep the circuit as simple as possible. Searching through Internet revealed the TDA2003 as the best alternative... It has 10W of power, and doesn't need a symmetrical power supply, thus making it eligible for portable applications. 
The schematic used. Source:

The schematic is pretty simple, It's nearly the same as the one you can find on the datasheet... I reproduced the circuit twice for stereo. 
As power supply, a simple 12V 3Ah SLA battery was used. The speakers came from a car radio.
In the first version, the iPod was plugged in the headphones jack, with an annoyingly long cable. For this one, I wanted something clean. I bought a cheap iPod type connector to line out+USB cable off eBay for 4 bucks, and cut the jack to solder it directly to the amp. I kept a 3.5mm jack as alternate input, to plug in other devices.
Here is the Heavy-duty, more recent version... Still a simple box. I used a safety switch from RadioShack, thought it would look cool :)

Back of the device. I know, I have to tidy my wires up. The battery is hiding the circuit. In the upper part, you can see the "dock" cable.
Details of the amp. Simple, but powerful circuit. I added two heatsinks, but they never get very hot.

As for the case, I didn't want anything fancy... Remember: Keep it Simple. That's why I stuck to a simple wooden box. I never tried at full power yet, but at half throttle, it's already loud enough to be heard quite a distance away. Normally, the battery lasts for at least 3hrs, at medium power, without charging. It also includes an external power plug, that way I can use it when the battery goes flat (as for the charging, I'm using an external charger... I have to figure out something more portable). Still not audiophile quality, but it's already pretty good, I can't hear any distortion. 

The dock also has a charging feature (By sending 5v in the USB power line, along with 2.5V in the D+ and D- to trick the iPod into thinking it's plugged into an official product), but for the sake of autonomy, I added a switch to turn it off when not needed. I still have to fix a problem with the 5V regulator, it gets VERY hot, even with a heatsink, which is weird as the 7805 is rated at 1A, and the iPod Classic charges at 500 mA.

The only drawback I can think about is the weight: 3.5kgs! 7 times more than the first version... I had to lose a bit of portability for the benefit of power.

Total cost? 25€ (or $30)

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