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How To Add Independently Powered Speakers to a Home Audio System On The Cheap should have been added to the title but I figured it wouldn't fit on the little thumbnail.  I found similar setups all over the internet but did not see any quite like this.  I am entering this in the A/V contest but also intend it to inform readers of how to do this and how to troubleshoot a particularly nasty problem... HUM!

The first step is to secure for yourself the following items:

An unwanted amplifier (you might have to fix it)
Sufficient length of wire
Appropriate audio connectors
If you use a car amplifier you will need a power supply unit that will match your amp (same or close in Watts and must be 12-14, maybe 15 volts)
Of course, some speakers not currently being used.
You may need an extension cord to troubleshoot hum

Step 1: Your Amplifier

Your amplifier will probably be different than mine.  Hopefully you got it for free and didn't have to fix it (something like I try to show off in these pictures...)

You need these things to work on your amplifier:

Inputs for a signal, probably RCA or the like
Outputs for speakers
Power

You can just plug in another normal amp and hookup the speakers and turn down the treble and turn up the bass but where is the fun in that?

If you are using an amplifier intended for use in a car then you will need to look online for the owners manual and it will tell you how to hook it up.  Just hook up regular speakers like they were a subwoofer.  If your speaker has a mid range driver and/or tweeter they just will not be used (unless you have an amplifier that supports those frequencies).

Step 2: The Real Trick Is...

...the "record out" feature... don't underestimate the power of a line level signal source.  My home stereo amplifier has four or five of these outputs in addition to a pre-out going to the main power amp for everything else.  One of these record out lines is what I use to get my signal throughout the house.  Just run a line from the record out to another amplifier and your system can expand greatly. You do not need very thick wires... I have done this phone line and had no problems but here I used 18 gauge because that was the smallest I could get at the store and I wanted to do this today.  I got 100 feet for 13 dollars... you can probably get a better deal. 

To make the signal cable I just sacrificed an old audio RCA cable and tied the ends onto my purchased cable and wrapped with electrical tape.

Step 3: It Works!

What you see here is a 300 Watt 12 Volt amp powered off a 300 Watt (280 Watt, 15 Amp) power supply with two 75 watt, 4 ohm speakers in parallel (because it is a mono amp).  I do not power it more than a third of the way up or I get yelled at so I do not worry about my power supply exceeding its limits...

Turn it on and...

MAJOR PROBLEM

When you have units powered from different outlets you have the chance of HUMMMMMMMMMMMMMMMM!

It is awful, you will hate life when you hear this hum from your audio.  So if you don't know this already....

You have two possibilities in US houses to get 120ish Volts on an outlet and they are out of phase with each other.  These two possibilities exist because being out of phase allows a third configuration which is used for getting 240ish volts.  If you get power to your audio system from both of the possibilities you will probably get a hum.  If you setup a system that spans your entire house you increase your chances of this occurring.

So, how to solve the problem?   Plug everything into the same outlet (power strip) or at least the same wall.  You may have to try various outlets but you will find one that makes the hum go away... probably.  This is where the extension cord comes in.

Enjoy!  Sorry no video as baby is sleeping and this really gets loud... I shouldn't have waited until the last minute for this contest.  I figure I can reach 200ish watts but will probably be more around 75-100 watts when I use it because it is so loud.

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