The Carl Martin Dual Injection combines two transparent boosts, each with its own Level control and true-bypass footswitch. A toggle switches between Serial and Parallel modes. Serial engages an Input/Output 1, which places the boost anywhere in the signal chain. Parallel mode connects Output 1 before a drive or other preamp, and uses Input/Output 2 to connect to the effects loop of an amplifier. This allows for four boost settings. The Dual Injection operates on a 9-volt battery or a regulated power supply and is housed in a die-cast case with large  knobs and LED indicators. For more, go to http://carlmartin.com.