DIY: Subwoofer amplifier power supply from an (old) ATX PSU

I was broke and needed a quick and easy way to set up a subwoofer for my Home Cinema/Gaming setup (Currently using a Pioneer VSX-D514 receiver). I got this subwoofer with a 20 liter case and an ATX Power supply for doing a couple of friends some favors.  (A high-quality amp+psu can cost well over 300USD).

Luckily I aleady owned a car-amplifier rated at 2x800W @ 12V. I only use one of these because the receiver only has a single MONO-channel subwoofer output.

The ATX Power-Supply was a mid-/high-end 1000W (Rated at 12V/80A). This one has two 12V rails marked +12V1 and +12V2 each capable of sucking up to 40Amps each. Pretty nice :-)

NOTE: This is just the first revision. This article will be updated when I do something new

Tools needed:

  • Just to be on the secure side: Insulated gloves
  • Probably Phillips screw-drivers, or those flat ones at different sizes. (I prefer a driver with bits)
  • Pliers, Scissors, Wire-cutter/stripper (or your teeth)
  • Duct tape, strips – Or even better shrinking tubes
  • Soldering iron (the more expensive, the better)
  • Soldering tin and flux
  • A Multimeter may come in handy

Shopping List:

  • A subwoofer [in a cabinet]
  • A subwoofer amplifier (Preferably a Mono-block)
  • ATX Power supply that can withstand the amplifier wattage (Ohm’s law)
  • Cable from receiver to the subwoofer amplifier
  • Cable speaker from amplifier to subwoofer
  • [Alternatively] A switch to enable ATX-power (See “Making the PSU power up” section)

ATX Power-sypply hacking:

Schematics are located at the bottom of the page.

Open up the case:

First open the case and clean it out for dust etc. Remove all the covers so you can easily manipulate the wires.

Cleaning up the cable mess:

  • First of remove all of the Molex plugs etc. (clip them of next to the plug).
  • Then collect all the YELLOW wires and strip/tape them together (+12V)
  • Then collect all the BLACK wires and strip/tape them toghether (- / Ground)
  • All the other wires are either +3.5V or +5V, you don’t need these, except the GREEN wire. This one is used for powering up the PSU.
  • Now make all the YELLOW, BLACK and GREEN wires the same length (some soldering required here, and isolation).
  • Then solder all the BLACK  wires together (bundle them up, so it looks like a thick power-wire)
  • Then solder all the YELLOW wires together (bundle them up, so it looks like a thick power-wire)
  • After the above steps is complete use shrinking-tubes/tape/strips or whatever to nicely place the wires inside the case so they do not touch any of the components, and does not come in the way of the fan. (Also make sure not to mess up the air-flow)

Now you just need to stick the YELLOW, BLACK and GREEN wires out of the ATX-casing.

You may need to drill a new hole for this, but most ATX-cabinets comes with a circular-hole that should fit quite well.

Making the PSU power up:

First make sure you have not connected the main power cable, then turn all switches off.

Alternative 1: Powering on using main-switch:

Just short the GREEN wire and a BLACK wire.

Alternative 2: Powering on using secondary-switch:

For the power-on switch we need to short the GREEN wire and a BLACK wire. Attach and solder a switch between these connections.

Test PSU after modifications:

First make sure all switches are turned off. Plug in the main power cable and turn on switch(es).

If no fuses went out an the fan is running, this is working.

If you have a multimeter check if the voltage output is at least 12.0V. 

Wiring it up to the Amp:

  1. Connect the BLACK wires to the GND connector on your amp
  2. Connect the YELLOW wires to the +12V conncetor on your amp
  3. Bridge a wire from  the +12V connector to the SIGNAL connector on your amp

Before connecting the speaker be sure the amplifier receives power (should be indicated by an led).

Results:

Sounds really good! For the best depth I had to set my Amp to Pass-through and the Receiver X-over to 200 Hz.

Schematics:

Gallery:


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