Current consumption. All electrical equipment uses current. Most audio devices dont use much (a few milliamps - a few thousandths of an amp - in many cases), so you can generally run a bank of processors and effects units without overloading a single 13A power point. Power amplifiers - the things that do the physical work - are the part of the audio chain that use the most current, although their current demands are usually less than you might expect. All the same, it is important to ensure that any load on the mains supply is less than the supplys rated current capacity. Where several amplifiers are used at the same time (e.g. tops, subs and monitors), their total current consumption should not exceed 13A if they are supplied through a single power point, or the current rating of the mains circuit - often 20A in domestic or village hall circuits - if they are supplied through multiple sockets on the same ring. Larger touring systems usually use dedicated supplies of 32A or more. Power is the product of voltage and current: Power (P) = Voltage (V) × Current (I). In theory, therefore, your 3kW system needs: P (3,000) = V (230) x I I = 3,000 ÷ 230 ≈ 13A. In practice, however, amplifiers driving a musical signal never run at full power. If you tried to get them to run at full power with a musical signal, the signal would be badly distorted, and any amplifier with thermal or current overload protection would shut down within a few minutes. Any amplifier without protection would fail fairly soon. Most amplifier specifications will give information about power or current consumption under some or all of the following conditions: •Idle - also called No Load or Quiescent - Current. The current consumed with no signal present. •1/8 power (sometimes 1/6 power is given instead). The current consumed under normal operating conditions. 1/8 power represents the average power of a musical signal driven to occasional clipping. •1/3 power. This represents the power used by a system that is being driven very hard (with severe clipping). It would already sound poor at this stage, and any further increase in level would make it worse. •Full power. This is what would be required to drive a continuous sine wave at maximum level. Thermal or over-current protection - otherwise failure - would happen fairly quickly if you tried this, but why would you? If you are designing a PA system, you should generally base your expected total current consumption on 1/3 power (and at least 1/8 power). Note that power or current consumption at 1/8 power is greater than 1/8 of the amplifiers output power. Some of the power drawn from the mains is converted into output power, and the rest of it is converted into heat. Useful extra features include: •Thermal overload protection. If the amp gets too hot, temporary shut-down is a lot less inconvenient than component failure or fire. •Over-current protection. If the amplifier tries to draw too much current, it will limit or shut down. •Short-circuit protection. If the loudspeaker + and − leads are shorted together, the amp will overheat and either shut down or burn out. Short-circuit protection prevents the amplifier from trying to drive a short circuit (over-current protection will also protect against shorted outputs). •D.C. protection. If D.C. is detected on the output terminals the amplifier either disconnects them (usually using a relay), or shuts down the power supply. If a fault develops in the amplifier, it stops there. Without D.C. protection, you might lose speakers as well.
Posted on: Mon, 01 Sep 2014 12:20:40 +0000
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