The quarter inch jack ("phone
connector") is probably the oldest connector still in use today,
and it's picked up a very wide range of applications. Which also
means it's a huge mess in a live sound context, where a 1/4" jack
could be any of:
Unbalanced or balanced line level (~1V). Ex: a
mixer to a powered speaker.
Unbalanced instrument level (~200mV), high impedance. Ex:
electric guitar.
Unbalanced piezo level (~50mV), high impedance. Ex: contact
pickup on a fiddle.
Unbalanced speaker level (~30V). Ex: powered amplifier to
passive speaker.
Stereo line level (2x ~1V). Ex: output of keyboard.
Send and return line level (~2x 1V). Ex: input to and output
from an external compressor.
Switch (non-audio). Ex: damper pedal on a keyboard, which would
be normally open or normally closed.
1V per octave (~5V). Ex: older modular synth.
Here's a compatibility matrix with a bunch of these:
If you plug _____
balanced line level output
electric guitar output
powered amplifier output
stereo line level output
effects loop (mixer side)
Into ____
balanced line level input
✓
too low, bad timbre
boom!
left - right
no audio
DI input
distortion w/o pad
✓
boom!
distortion w/o pad, right channel dropped
no audio
speaker input
nearly inaudible
no audio
✓
nearly inaudible, right channel dropped
no audio
stereo line level input
✓
too low, bad timbre, right channel no audio
boom!
✓
no audio
effects loop (mixer side)
no audio, possible damage
no audio, possible damage
boom!
no audio, possible damage
no audio, possible damage
Note how few "✓" cells there are.
As much as possible, set things up to avoid 1/4" connectors. If you
use Speakon to
connect amplifier outputs to passive speaker inputs and XLR for
balanced line level signals you'll avoid all the "boom!" outcomes,
along with most of the ways of connecting an output to an output. You
can't get away from them entirely, but ideally the only 1/4" cables on
stage are short runs to DIs.
The quarter inch jack (" phone connector") is probably the oldest connector still in use today, and it's picked up a very wide range of applications. Which also means it's a huge mess in a live sound context, where a 1/4" jack could be any of:
Unbalanced or balanced line level (~1V). Ex: a mixer to a powered speaker.
Unbalanced instrument level (~200mV), high impedance. Ex: electric guitar.
Unbalanced piezo level (~50mV), high impedance. Ex: contact pickup on a fiddle.
Unbalanced speaker level (~30V). Ex: powered amplifier to passive speaker.
Stereo line level (2x ~1V). Ex: output of keyboard.
Stereo headphone level (2x ~3v). Ex: headphone jack.
Send and return line level (~2x 1V). Ex: input to and output from an external compressor.
Switch (non-audio). Ex: damper pedal on a keyboard, which would be normally open or normally closed.
1V per octave (~5V). Ex: older modular synth.
Here's a compatibility matrix with a bunch of these:
Note how few "✓" cells there are.
As much as possible, set things up to avoid 1/4" connectors. If you use Speakon to connect amplifier outputs to passive speaker inputs and XLR for balanced line level signals you'll avoid all the "boom!" outcomes, along with most of the ways of connecting an output to an output. You can't get away from them entirely, but ideally the only 1/4" cables on stage are short runs to DIs.