Quarter Inch Cables are Devious
post by jefftk (jkaufman) · 2025-04-05T02:40:05.054Z · LW · GW · 2 commentsContents
2 comments
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:
| 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.
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comment by cousin_it · 2025-04-05T15:46:07.433Z · LW(p) · GW(p)
ideally the only 1/4″ cables onstage are short runs to DIs
And all the pedalboard stuff that happens before the DI. But mostly I agree.
Btw, do you already know that a piezo signal is much improved by a preamp with >1 meg ohm input impedance? I figured that out with my electric cello.