Tech Talk would like to briefly assess the ins and outs of inputs and outputs, because the two terms are often interchanged mistakenly, in reference to both instruments and amps.
Plugging things in is where the terminology can get confusing. For example, the jack on your guitar or bass is where you plug in the cable, so it’s common to refer to it as the instrument’s input jack. That, however, is incorrect.
That jack on your guitar or bass where you plug the cable in—the one you’ve been calling an input jack all this time—is actually an output jack. The key to knowing the difference is understanding the signal path, or the direction in which the signal is traveling. Where is the signal going? Follow the signal path—the signal is traveling out of your guitar or bass to the amp.
And the jack on your amp where you plug in the other end of that cable? That is an input. It’s where the signal comes in from the instrument.
Does your amp have a headphone input? No, it doesn’t. If you can connect headphones to your amp, then your amp has a headphone output. A signal is traveling out of the amp and into the headphones.
The “aux in” jack on your amp, however, is just that—an input. The signal from your mp3 player, CD player or other outboard devices is traveling in to the amp.
Similarly, the “line out” jack on the back of your amp is just that—an output. The signal is traveling out of your amp to some other destination, such as a PA system or recording gear.
For those of you who have a head/cab rig, the speaker jacks on the back of the head are outputs; they send the amplified signal out to the cabinet. The speaker jacks on the back of the cabinet are inputs, as they receive the signal coming from the amp head.
If your amp has an effects loop, the effects send jack is a preamp output that routes the signal to your effects. The effects return jack is a power amp input that receives the signal from your effects coming back into the amp.