The fP 3400 is a lightweight and space-saving power amplifier, ideal for use in high quality touring sound systems as well as in demanding permanent installations. Heat and cooling are fundamental problems in many extreme high power amplifiers similar to the fP 3400. In 1990, Lab.gruppen patented a high efficiency amplifier called fP 3400. This development was an evolutionary step past the Class D amplifier. Lab.gruppen call this unique step forward: Class TD. This stands for: Tracking Class D. Class TD obtains the same high efficiency as Class D, while avoiding the main drawbacks. Class D has a power-amplifier topology using Pulse Width Modulation (PWM) to achieve high efficiency, but it needs a recovery filter between the output stage and the loudspeaker. Lab.gruppen’s Class TD amplifiers do not need this filter and this is one reason why the Lab.gruppen Class TD obtains the same sonic quality as a traditional Class AB amplifier. To meet the demands for a flexible gain structure in the system, Lab.gruppen offers a multiple position gain switch. The maximum amplifier gain can be set to all industry standards: 20, 23, 26, 29, 32, 35, 38 and 41 dB. The regulated power supply easily deals with a very high variation in the AC mains voltage:it can drop by up to 20% below its nominal level – e.g. to 180 V instead of 230 V – without any problem.