Question: Will anything bad happen if I use a Y-cable on my CD player or laptop to hook its two outputs into one input on my mixer? I’m running out of channels.
Answer: The answer is yes, probably. If not immediately, then some time in the future. What happens is that most modern audio gear has a very low output impedance, typically under 100 ohms. This is great in that it can drive audio over very long cable runs while ignoring interference from light dimmer buzz and cell phones, but bad in that a short circuit will cause its output transistors to put out too much current and overheat, eventually killing them.
But here’s the crazy thing…if you’re running the exact same signal out both the left and right outputs of your CD player, laptop, or iPod, say from a mono sound track, then there will be no current flow between the left and right output stages and all will be well.
However, if you then play a music track with a lot of dissimilar info on the left and right channels, say from a split-track song with music on the left channel and guide vocals on the right channel, then there will be essentially a short circuit current between the left and right output stages. This is very hard on the CD player’s and iPod’s electronics, and they will begin to overheat internally.
So if you only play these backing tracks once in a while or for only a few minutes at a time, then the output stages may never overheat enough to burn out. However, play these same backing tracks for an extended period of time (perhaps 30 minutes) and you’ll probably find that one of the outputs of your CD player, laptop, or iPod has been burned out. Not a good day for your gear.
The best way to combine two outputs into a common input is by using a box with special build-out resistors that limit this current. Whirlwind makes a box called the podDI that not only safely combines the two output signals from the sound source into a common input on the console/mixer, it also gives provides separate volume knobs so you can turn the left and right channels up and down in volume independently. (The podDI is pictured above with a Y-splitter.)
In addition, it provides a balanced XLR output transformer that’s perfect for isolating the ground of your gear from the PA system and stopping that nasty power supply buzz that often occurs when using a laptop as a sound source that’s powered from its own 120-volt transformer.
You can buy one for about $75 from Full Compass Systems here.