Audio Splitter
I needed a way to feed audio out from my HF receiver to several different inputs.  I decode HF digital signals, so I wanted to feed audio out from the radio to the input of a computer sound card.  I also wanted to feed audio to the sound card of a second computer that I use for both digital decoding and digital recording.   On top of that, I also needed another output from the radio for my headphones. 

I had tried those cheap headphone splitters but was not happy with the results.  They always seemed to not work very well, giving intermittent audio, and the worst part was I had one fed into the other, and all of this stuck into the external speaker jack of my Icom R75.  I didn't want to put a lot of strain on the external speaker jack.  I also had problems with ground loops among several radios & audio devices, which manifested itself in the form of a 60 Hertz hum in the speakers or headphones.

I had already built both an
audio isolation transformer and an antenna splitter, so I knew it would be an easy job to build a similar device to split audio out from a radio to several different inputs.  The device I came up with was very similar to the antenna splitter I had previously built, only I added two more outputs.  The end result was a passive four-way audio splitter that I could feed audio from my HF radio to various inputs.  The bonus is that this device also works as an audio isolation transformer, so that you can hook one of the outputs directly to a computer soundcard without any danger of blowing the soundcard that there would be if the audio was connected directly to the soundcard input.
The audio splitter was constructed by winding five pieces of magnet wire around a toroid that I had salvaged from an old PC board.  All five lengths of wire were wound together making a 1:1 transformer between the input and the outputs.  I made about 10 turns or so around the toroid, filling the entire toroid with wire.  Once that was done, I removed the enamel from the ends of the wire, and using a continuity checker found both ends of each wire. 

I drilled holes in the sides of an Altoids box and installed five mono 3.5" phone jacks.  I then soldered both ends of a winding to each jack, one on the audio side and one on the ground side. Once that was done, the splitter was complete.  The stiffness of the wire holds the toroid in place, and since it is inside a metal Altoids box I don't have to worry too much about RF getting into the audio chain. 

Since all windings are wound the same way and provide a 1:1 impedance match across all the audio jacks, it doesn't matter which jack is used as the input and which are outputs.  As long as audio is fed into just one side of the transformer, the other windings will act as outputs.  On the other hand, if someone wanted to mix two audio sources into one output, this design would work for that as well.
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