How to Choose a PA Mixer AmplifierHow to Choose a PA Mixer Amplifier

This is the only calculation that must be done before anything else, and it is straightforward. Add up the tap setting of every speaker that will be connected, then add 20 to 30 percent headroom.

A small office with eight 10W ceiling speakers needs 80W of load, so a 100W amplifier is comfortable. A school corridor and classroom system with thirty speakers at 10W is 300W, which points at a 350W or 500W model. Under-sizing means distortion on peaks; over-sizing costs a little more and gives room to expand later.

A zone is an area whose level can be controlled independently. If the whole building should always hear the same thing at the same volume, one zone is enough and a single-channel model such as the MP-7070 is the economical choice.

Most real buildings are not like that. A school wants the corridor loud and the staff room quiet. A hotel wants music in the lobby and nothing in the meeting rooms. Once that is true, a zone controller amplifier is worth the extra cost — the SA series gives five zones with independent adjustable knobs, and the USB-800F gives eight zones with switches.

Count zones by asking how many areas need a different level, not how many rooms exist. Six classrooms that always run together are one zone.

Count your microphones and your playback sources, then check them against the amplifier's I/O. The MP-7070 provides one MIC and two AUX inputs, which suits a single paging microphone plus background music. The SA-100VCM, SA-150VCM, SA-350VCM and SA-500VCM each provide three MIC and three AUX inputs plus an AUX output, which covers a lectern microphone, a roving wireless receiver, an emergency microphone and a music source at the same time.

Most models in the range also include Bluetooth, FM radio and USB or SD playback built in, which removes the need for a separate media player. Several add a remote controller or an LCD screen, and the SA series includes a CHIME button for announcement pre-tones.

Class AB is the traditional design — reliable, well understood and used across most of the SA series. Class D is a switching design that is far more efficient, which means less heat and a much smaller chassis for the same output; the AMP-100 uses it to fit 100W into a 220 x 200 x 44 mm case. Class H is a variant used at high power for efficiency, as in the USB-800F which runs Class AB at 800–1000W and Class H at 1500–2000W.

For most installations this is not a decision you need to agonise over. It matters when rack space or ventilation is tight, in which case a Class D model is the easier fit.

Look at the protection specification, particularly for systems that will be left running unattended. Some models list simple protection; the AMP-100 and USB-800F specify full protection covering short circuit, overload, over current and DC fault.

For a system that runs all day in a school or a factory, that difference is worth paying for. It is the feature that turns a wiring fault into a tripped protection circuit rather than a failed amplifier.