This is an important topic; careful power-supply selection can make a big difference to the life of any electronics device, including this harddisk-based MP3 player.
Ideally your power supply will be capable of 2 amps continuous. A 1.5 amp supply might work OK, depending upon your harddisk requirements, but there’s no guarantee; you would have to try it and find out. Two amps is the recommended current rating.
This is a critical number. The stated range is 12.5 to 16 volts DC. But there are some considerations here.
Ideally your power supply will be towards the low-end of these voltages; say 13 or 14 volts or so. The problem with the high-end voltage is twofold:
- You will blow the fuse if you go above 17 volts. The tranzorb D1 will conduct with high input voltages, blowing the fuse to protect the board. U1 in particular has an “absolute maximum” rating of 20V, hence the presence of its protector, D1.
- U1 is a linear regulator. It outputs 12 volts for the diskdrive. It has to drop the difference between your input voltage and its 12V output voltage. The greater that voltage difference, the more it has to drop and the more power it dissipates. At 17 volts input it can easily be forced to dissipate 2.5 watts or more. This heat generation can destroy U1 very quickly unless it has a decent heatsink on it.
If you have a powersupply at the higher end of the voltage range, you have a couple of easy options.
First, decrease your power-supply voltage by placing some power (or rectifier) diodes in series with its output. Diodes such as the 1N540x (where x is 0 – 8; 1N5404 is a popular example) are common, cheap, and do the job well. But pretty much any power or rectifier diode capable of handling 2 amps or so will do. Each diode will drop around 0.8V (almost a volt), so several diodes in series can make a significant difference. The diodes will get a little warm; each may dissipate about half a watt, so place them in such a way they can cool off. (Wrapping them up tight in plastic insulating tape may not necessarily be the best idea.)
Second, ensure you have heatsinks on U1 and U2. U1 in particular can overheat and die quickly if a high power-supply voltage is used. Heatsinks are discussed at the end of the construction notes page.
The combination of diodes to drop the input voltage, plus heatsinks on U1 & U2, should keep your MP3 player happy for a long time to come.
Ensure your power-supply has adequate regulation; ie that it doesn’t have excessive ripple on its output. The MP3 player has a large capacitor on its input to assist (greatly) with that, still, a super-cheap power supply could provide too much ripple. A transformer followed by a single diode would not be adequate! <grin> Pretty much any commercial power supply meeting the voltage & current requirements should be fine, but if you’re building your own supply from parts please keep that in mind.
The power connector on the player is a 2.5 mm “bullet” power jack, with the inner barrel positive and the outer shell grounded.