The word “re-amp” (or at least the un-hyphenated “reamp”) may be a trademark of Radial Engineering, in which case, please don’t sue me. This isn’t for sale, and no one would confuse it with anything good. I think “re-amper” is like Kleenex or Band-Aid—a genericized trademark where the brand name is so well known that it can take the place of the general name of the object. Although, I can easily come up with “tissue” or “adhesive bandage,” whereas I have no idea what I’d generally call a re-amper.
I guess it would be something like “a line-level to instrument level signal converter,” which is too much to say, and certainly too much to write in purple Sharpie (which is also a trademark). My really quick and probably not-exactly-correct explanation is that an electric guitar puts out an “instrument level signal.” The pickups convert energy from the moving strings to a high-impedance, unbalanced electrical signal. Things that guitars are supposed to plug into, like amplifiers or effect pedals, are designed to expect this sort of signal. Instrument level signals aren’t good for much else though, so most other things in the audio world work on a “line level signal,” which is a low impedance, often balanced, more robust sort of signal that is better for moving audio information longer distances without degradation, etc.
So, what if you already had something recorded or it came from an entirely line-level world and you wanted to run it through an amp or an effect pedal? That’s when you use a re-amper, which converts a line level signal to an instrument level signal. I think it was originally invented to allow someone to record a raw, direct guitar track, focus solely on the performance, then run it through whatever amps/amp settings/effects they wanted later, but there are a bunch of uses for this sort of thing. I mostly wanted one so that I could do dumb stuff like make fake drums from my computer go through fuzz pedals.
This is a really simple device, cobbled together from several similar schematics that I found online. It’s completely passive, and is mostly just a transformer plus a ground lift switch and a level control. I’m not even 100% sure that it works correctly, since I’ve never owned a real one, but in practice, it’s better than just blasting a pedal with a line level signal. Most of my pedal building focuses on pretty trashy circuits, where a little chaos and noise is to be expected. This is a different sort of beast, and probably an area where I’d be better off just buying something off the shelf that underwent actual engineering, but it was an interesting experiment for under $20 in parts.
This definitely didn’t work correctly. I redid it, and it’s better now—it was mostly how the potentiometer was wired (and not wired). I’m still not sure that it’s doing much more than it would if it were just a volume knob, but at least it works as a functional volume knob now. In the process of updating it, I also replaced the speed knob with a chicken head knob. The speed knob was a little too “metal” for me, and I find that the chicken head knob imparts a certain vintage tone and warmth, evocative of old tube amps and gas stoves.