main PA amplifiers

PA Services
-large system
-small system
-musician info

12v PA info
-bike generators
-power control & batts
-gtr & bass amplifiers
-misc kit

domestic 12v info

lower voltages
-6v systems
-USB/phone power
-wind-up devices



A preferred way of providing power amplication for audio is using amplifiers designed for car use - these run from 12v DC (often a wide range, say 10-16v), are robust, often have usefully low output impedance, and are readily available. It's difficult to know what you're buying, though - power ratings are largely meaningless, normally given in 'PMPO', a fairly random multiple of the true, 'rms' value. It's difficult to generalise, but the smaller 'booster' amps are OK for smaller systems, say on one bike, and the bigger, long ones are more likely to cope with a band, such as the one below (rated 1200W across two channels, actually 200W RMS before clipping). Inputs are normally on phono connectors, outputs on screw terminals; it's best to mount these as part of a larger unit and bring the connections out as standard sockets.

[pic of car amp]

The lower panel above is the visible part of the main amplifier; it's an 17" long large car audio amplifier by SPLX. The amplifier consists of a step-up inverter section that provides power supply rails of approximately +/-45v; these are connected to a socket at the far end of the amplifier via high power rating 100Ohm resistors, to provide a dual rail supply for the mixing desk. Ideally this should be regulated down to +/-20v internally; at the moment the resistors drop sufficient voltage to allow the mixer's regulators to handle the input; inelegant, but it works.

Originally this was modified with power & speaker sockets replacing the screw terminals, but a second modification has it mounted on the rear of a 19" rack mount panel, with the inputs and ouputs brouoght out to the front; the power input is now on a socket on the rear of the unit. The large cast heatsink of the unit remains; that and the additional front panel seem to disspate the heat enough, although small computer fans could be usefully added.

The inputs are on the left (if no plug in the right channel socket, this channel is fed from the left input), and speaker outputs on the right; the centre socket is the bridged, mono output. A useful addition would be an input level control; one day.

A second, smaller amplifier is generally available to be used in bridge monde to drive one or two monitor speakers, when required. This is largely unmodified; the inputs remain on phono sockets, and the power in and speaker out connectors on flying leads. The ideal would be to mount this in the main 'crate' at some point.

(we also have a spare amplifier, actually a four channel unit wired into two bridged pairs. This is a spare for the main amplifier, and can also be used to drive the monitor speakers where necessary.)