Bass

This is my attempt at building myself a mains power amp, so I can connect my car bass box to my home stereo.

As most people know, car amps run off 12V DC and home stereos run off 240V AC.  So if you plug it in to the mains, it will go bang (just like Fergal-Burger did with his Rover boat!).  Unfortunately, a suitable mains power supply that can handle 20A at 12V (i.e. for a 240W amp) costs about 300 quid upwards!!

I found some people who had tried it with a computer power supply, but until now they haven't been cheap enough to handle 20A on the 12V output.  The latest range of 500W+ ATX12V supplies can deliver 240W at 12V output.

I bought a QTEC 550W el-cheapo power supply for 28 quid on the web.  Its bling bling gold colour with two fans for extra cooling.  The problem with these cheap power supplies is that they are "switch-mode" operated i.e. pulsed current with small capacitors, so you need to load the 3.3V and 5V outputs to 0.3A to stabilise the 12V voltage output.  I stripped it down and then put in some 7W ballast resistors of 6.7ohms and 10ohms poked in to the end of motherboard connector.  Also, power supplies will not boot up if one of the wires (PS_ON) is not held low (i.e. grounded).  A pair of dividers poked in to the end of the connector did the trick!  Two wires were run from the new type 12V connector to the amp.

It worked pretty well but if I turned it up too loud the sub would distort, which means the instanteous power for those big bass "punches" was not there.  That is due to the cheap small capacitors inside the unit.  The only solution is to bridge the power terminals on the amp with a phat capacitor of about 0.2+ Farads (like those big ones who get in ICE installs).  I can't be arsed to spend 25 quid on one at the moment but will try it at a later date.