The Electro-Harmonix LPB-1 - Linear Power Booster - is an exact recreation of the original LPB-1 circuit that ushered in the age of overdrive in 1968. You can put the LPB-1 in line with any effect to provide boost and definition, and improve the gain and saturation of your amp.
Electro-Harmonix LPB-1
Electro-Harmonix LPB-1