Mixer amplifier selection: power, zones and headroom

A mixer amplifier combines source selection, preamplification, zone routing and power amplification in one chassis. It may include a paging microphone input, a chime, a mute contact and a fire override input.

For a small building, one mixer amplifier can drive several zones. For a larger building, the mixer and the amplifiers may be separate units, or the system may use a network audio head end.

A zone is an operating area. Two adjacent rooms with the same schedule and the same source may be one zone; a corridor and a classroom are usually different zones.

The mixer amplifier needs enough zone outputs or a zone matrix that can route the sources. If the building needs all-call plus individual zone control, confirm that the model supports both.

Add the tap wattage of every loudspeaker on each circuit. A 3W ceiling speaker and a 15W horn speaker are not interchangeable in the load calculation.

If the connected load is close to the amplifier rating, the system has no headroom for a future speaker or a higher tap setting. Leave room in the schedule.

Use the connected load plus 25–50% as a starting range. The exact figure depends on the programme material, the protection circuit and the standby policy.

For a 100V line, check the current and the voltage drop. A long cable run can lose more level than the amplifier gain can recover.

List the sources: paging microphone, music player, tuner, auxiliary input and fire alarm. Confirm the priority: fire over paging, paging over music.

A mixer amplifier with a fixed priority may be enough for a small system. A larger system needs a matrix or a control layer that can route sources to zones.

If the system carries evacuation messages, the fire override must be a hard-wired input and must work without the network. Confirm the interface with the fire alarm supplier.

Monitoring may include pilot tone, circuit impedance or amplifier fault contacts. The requirement comes from the standard and the building, not from the amplifier brochure.

Use the table to check the model against the project. A mixer amplifier that meets the power but not the zone or priority requirement is the wrong model.

Send the zone schedule, the loudspeaker count, the tap settings, the source list and the fire strategy. Add the existing amplifier model if the project is a replacement.

We will return a load calculation, a model shortlist and the interface list. The final model is confirmed after the room data is checked.