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Power Packed: Multi-channel Amplifiers Move Up
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Lab.gruppen C Series amplifiers at Venture Christian Church, with Ben Dixon, Worship and Media Arts Engineer
Until the late 1950s, nearly all audio systems were mono and, of course, so were the amplifiers. Then along came stereo, and soon most amplifiers had channels in pairs. That certainly makes sense when you have two channels going to two speakers! Therefore, “stereo” became the format for nearly all power amplifiers.
But then more installations – churches included – moved to bi-amped and tri-amped speaker clusters, multi-way line arrays, subwoofers, front- and side-fills, delay systems, and auxiliary systems for adjacent rooms. To meet a demand for multiple channels, new power amplifiers for PA systems…well, until recently, they pretty much stayed stereo.
Why was that? Force of habit? To some extent, yes. But it’s also because technology was playing catch-up. Certainly the idea of putting four or eight channels into a single chassis was appealing, but there were practical limitations—particularly when high power output was needed. More channels would make the amplifier bigger and heavier, while more output stages would generate more heat. And, for the most part, high-power amplifiers were already big enough, heavy enough, and hot enough when the volume was pumped up.
However, over the last ten years or so, new technologies have kicked in to rearrange the playing field.
New Output Stages and Power Supplies
One key development has been the steady introduction of new, lightweight, and highly efficient output stages. The two best-known “generic” types are Class D and Class H, both of which might be termed “quasi-digital.” Also, several companies have developed (and patented) hybrid variants that incorporate some aspects of the newer designs while still, they claim, maintaining the sonic purity of Class AB circuits. In all cases, however, the bottom line is the same: more audio power coming out for the same electricity going in, and with less heat generated in the process.
The other big breakthrough, pioneered in the 1970s and now approaching near-universal adoption, is the switching power supply. This technology greatly reduces the size and weight of the transformers and capacitors needed to change the AC input current into DC supply voltages for the output stages.
Then we have the general miniaturization of electronics in general. Everything else needed in the amplifier, from LED displays to plug-in processing cards, simply got smaller and lighter. The time was ripe for packing more channels into a chassis.
Why Go Multi?
So, let’s assume you need at least four channels of audio power. Why go multichannel? There are four credible advantages: less space, more configuration flexibility, “greener operation” and – all other things equal – lower cost.
First, less space is a no-brainer. Although a few older, eight-channel models occupy a 3U rack space, most multichannel amps are 2U and a few even squeeze into 1U. The operative industry term here is “power density”. Multi-channel amplifiers simply offer more of it -- in one case packing four 2200 W channels (at 2 ohms) into a 2U space!
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Bruce Borgerson networks around the industry via Wavelength Communications while monitoring technologies at the First United Methodist Church of Ashland, Ore.
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