The engl_rb100 is a preamp mainly used in the guitar enthusiast community. If you own this product then you might find its schematics and other detailed information useful. However, if you are just looking for guitar amplifiers or guitar accessories in general then there are many options out there.
The amplifier is a key to a good music setup especially if you wish to perform in a concert however, another important accessory is the guitar straps. Pick the best guitar straps to have the most confident guitar setup.