That’s the same thing.
Your typical amp head is composed of both a preamp and a power amp. The preamp pre amplifies the signal to line level, the power amp amplifies it for the cabinet.
- Your instrument signal goes in the preamp in or usually said the “input”.
- When the signal goes out of the preamp, you can insert an effect using the “send” output, also called the “preamp out”.
- Once you’re done with your effects, you plug your signal back to your head into the “return” jack or “Power amp IN” to go in the power amp section of your head.
I made this diagram (sorry if some words are in French) but it may help you visualize how a head is built. ("Préampli" means preamp, and "sortie baffle” means Cab output as you can guess)
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