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Old 10-15-2009, 11:38 PM
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Join Date: Aug 2009
Location: Terre Haute IN
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Lightbulb How To Test Ouput of MP3 Players

How To Test Ouput of MP3 Players:
Thought people might find this handy.

What you'll need:
  1. 1 3.5mm cable (one you don't want to use for anything else after we're done with it)
  2. 2 16ohm resistors (preferably 1 Watt or more with 1% or lower tolerance) NOTE: You can use any resistance you would like to calculate the output at that load, most players spec sheets show the output at 16ohms.
  3. 1 Multimeter (AC Voltage and Resistance measurement required)
  4. 1 Pair of Wire Cutters
  5. Electrical Tape
  6. 1 Utility Knife

Lets get started:

First you will want to cut the 3.5mm cable to approximately 12 inches. Then using the utility knife carefully strip off the outer insulation about 1 inch. You will find 3 or 4 wires, 2 hot wires with insulation and either 1 or two ground wire(s). Using extreme care strip the insulation off of the two wires. They are very small and easy to cut through the wire, if you do cut it just cut the entire cable and start over(thats why we have 12inches of cable). If there are 2 ground(uninsulated) wires twist them together. Now take the resistors and twist one side of each and the ground(s) together. Next twist one hot wire to the opposite end of one resistor and repeat for the other hot wire. Now using the electrical tape, tape one hot wire to prevent it from shorting out the other hot wire or the ground. Align the uninsulated hot wire and the ground(s) so they will not touch. If you striped too much of the hot that is not taped that it could contact the ground easily you can apply a small amount of tape to prevent it shorting out. Don't completely tape the hot wire or you will not be able to connect the meter.

You are almost ready to measure the output of your player. Set your multimeter to OHMS and Connect the leads to the ground and one hot wire(I use alligator clips on my meter leads, but you can just touch the wires). Make note of the reading if you used 16ohm resistors it should be 16ohms +/-.

Now put the mp3 file I uploaded on your player and connect the 3.5mm jack. Set your multimeter to AC voltage(if it does not select the range for you set it to best display 0.01-1 volts) and connect the leads to the hot and ground wire like you did above. Start playing the mp3 file mentioned above and make note of the reading(after it levels off) on the multimeter(ie: The Zune HD had an output of 0.6 volts). After you get a reading stop the player and turn off the multimeter to save the batteries.

Now to the math YAY!

The equation we will be using is as follows:
P = (V^2) / R where P is power output in watts, V is voltage in volts, and R is resistance in ohms. Get your scientific calculator out or a piece of paper and square the voltage and then divide by the resistance. If we use the Zune HD as an example we would square 0.6 volts to get 0.36 then we divide by 16 ohms to get P=0.0225 watts. If you want to convert to milliwatts just multiply by 1000 and we get 22.5 mw.

Now I'm sure you're thinking thats a bit of work just to know what a spec sheet can tell you, but do we really believe everything we read? I hope you enjoyed reading this how to, I enjoyed doing it. I'm sorry I don't have any pictures at the time of posting, I left my camera at work and I know my cellphone won't do this justice. I will submit pictures this weekend. Feel free to ask questions.

On a side note you can use the same process to test the output of any amplifier, you will need a resistor to handle the output of the amplifier(ie don't use a resistor rated at 10watts for a 100watt amplifer).

-Cory
Attached Files
File Type: zip 440hz_60s.zip (939.3 KB, 1 views)
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