LINE-LEVEL SOURCES Anything which provides an audio signal of at least three-quarters of a volt (775 millivolts) can be considered a line-level source. Such a tiny amount of electricity is still several times greater than anything a microphone can generate and greater again than the output of the average guitar pickup. However, line-level signals are much less powerful than the output of an amplifier, even the tiny variety which powers headphones.
It is important to keep these facts in mind because you may be connecting a wide variety of sources to the mixer and all of them will require specific input gain adjustments. "Speaker" outputs however, should not be connected to a mixer at all unless first put through a "direct box" with a speaker-level input and a line-level output. "Headphone" outputs have two problems; first they are speaker-level which means that they may distort the mixer input, but the signal is much weaker than the output of a regular amplifier so you may find that a direct box attenuates (reduces) the signal too much. The other problem is that headphone outputs are usually stereo so you will either need a stereo direct box and a mixer with stereo inputs or a stereo-to-dual-mono adaptor so that the signal can be split into left and right mono signals and fed to separate mono direct boxes and then to separate mixer channels (or you may decide not to use the headphone jack as a line output - a wise choice).
Here is a list of line-level sources and the outputs to use:
For information regarding line-level connections, see "LINE" under MIXER INPUTS.
