Utra Simple Headphone Box
By John Fisher
Here is a very simple passive headphone box that I have made that works really good. I have used this headphone box in several recording studios that I have worked in and have made them for different people. Because there are no active components, there is very little that can go wrong with it and it is very quick to make. I have used this headphone box where I had to record backup vocals with several people at a time.
Because there are no potentiometers, you are not able to adjust the individual volumes of each headphone. It is also recommended that you use headphones that are similar to each other, especially the impedance. If not some headphones will be louder than others.
You have to rely on the power of your power amp or your headphone out of your amp or your mixer headphone out to power it. Each channel of each headphone has a resistor in series that acts as a buffer . This is so that the load of each headphone will not effect each other or at most, very little. This is the same principal as how audio mixers work. Depending on if you are using a power amplifier or a signal from a headphone out on a mixing board you will have to experiment with the resistor values. If the signal came from a headphone out on a mixer I would normally use 180 ohm resistors. I wouldn't go too much lower as you will start to notice volume cuts on the headphones as more headphones are plugged in. This is not a terrible thing, but this means that the load of the headphones are starting to effect each other. If I was using the speaker out of a solid state studio power amp (100 watts or so), I usually use 280 to 330 ohm resistors. In either case, your volume is controlled from your power amp volume or your mixer headphone out volume.
Here is the circuit diagram. Al resistors are 1/2 watt. Carbon resistors are ok. All jacks are stereo 1/4" headphone jacks.
I built it in an old plastic box that I had in my junk box. Plastic is ok as you don't need any special metal shielding for this project. Even the cable that runs to your mixer or your amp does not need to be shielded as in most audio input cables.
For getting your signal from an amplifier, the most convenient way to use the headphone box is if you have a "A, B," switch for the speakers on your amp. For example you can use position "A" for your speakers and when you want to record without hearing the speakers you can connect the headphone box on speaker out "B". If you do not have an "A, B" switch on your amp, you will have to make one like I had to do.
Here is a diagram how to hook up an "A,B" switch. The switch is a DPDT switch. (double pole, double throw). All ground wires are hooked together. For my headphone box I used a 3 wire cable to run to the amp.
Here is the outside of the plastic box where you plug in the headphones. You could add more headphones if desired but then the more headphones that are plugged in the weaker the volume will be.
I have actually rigged up these things for meetings where someone was doing a running translation for a small group of people. Another "home" use could be when you and others want to watch TV late at night and you don't want to disturb anyone.
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