Four channels amplifiers: MPA4-80 and MPA4-150/400 Both four-channel models offer the same operating possibilities but differ substantially in two basic aspects apart from their output power. The MPA4-150/400 uses SPM Technology, while the MPA4-80 and MPA6-80 both use conventional technology. Additionally, the MPA4-150/400 includes active high-pass and low-pass filters for bi-amplification systems. These are the basic operating modes for these two models: Four mono amplifiers for four different mono inputs When setup this way, the MPA is able to amplify four different audio signals, each one having a dedicated volume control. Four mono amplifiers for one common mono input The amplifier operates now with just one input signal for all amplifiers, but preserves the ability to control each channels volume independently. This setup is useful when distributing signals to different zones. Four mono amplifiers for one common stereo input This setup is similar to the previous example but the input is now a stereo signal. The amplifier adds both stereo channels together converting them into a mono signal. Two stereo amplifiers for two different stereo inputs Each stereo channel offers a dedicated volume control. Useful for addressing two zones with two different stereo signals. One stereo amplifier and one bridged amplifier for one common stereo input Useful for bi-amplified setups, with two amplifiers for mid-range speakers and tweeters and a third (bridged) amplifier for a subwoofer. MPA Most remarkable features - Individual input sensibility for each channel with sealing possibility to avoid unwanted manipulation - Signal presence and clipping indicators for each channel - Balanced inputs via XLR connectors - Standarized out-put connectors - Convection cooling featured in MPA4-80 and MPA6-80 models - Low noise forced ventilation featured in MPA4-150/400. Dual Slope Controlled Fan System (see graphic). - Totally protected against shorting, DC at the output and overheating