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Highly Capable: The Evolution Of Outboard Power Amplifier Platforms

A look into the latest advancements, along with some benefits of rack-mount amps over powered loudspeakers.

By Craig Leerman October 9, 2017

Many predicted that digital technology would completely replace analog in professional audio, and I’ve heard just about as many also predict that powered loudspeakers would replace passive models driven by outboard power amplifiers.

Well, it seems that analog is here to stay, and so are power amplifiers independent of loudspeakers.

Benefits of passive loudspeaker/outboard amplifier approach include:

— Only needing to run a single cable per loudspeaker, particularly handy with stage monitors because it can reduce the clutter on deck.

— A distributed power scheme is not required. A power cable to each amplifier rack is usually all that’s required instead of running a power cord (and often an extension cord) to every loudspeaker.

— Hum and buzz problems can be reduced or eliminated by running power to an amplifier rack as opposed to plugging powered loudspeakers into various power outlets around a venue.

— The ability to put multiple loudspeakers on a single amplifier channel. If an amplifier (or channel) goes down during a show, a second (or more) loudspeaker(s) can often be driven by a single amplifier channel as long as the impedance is within the amplifier’s limit. If the amp in a powered loudspeaker dies during a show, that loudspeaker is out of commission.

— Passive loudspeakers weighs less than the same cabinets, so moving, stacking and arraying may be easier. A flown array weighs less as well.

— Depending on the system and approach, the operator can have quicker/easier access to the amplifiers and their controllers/crossovers for adjustment and “tweaking.” gives the operator a little more control over parameters.

— Passive loudspeakers don’t contribute fan noise.

— Do-it-yourselfers who like to design and build their own loudspeakers aren’t limited to only the available amplifiers for powered platforms, and/or they don’t have to design and build amplifiers for their boxes.

My company exclusively utilizes passive stage monitors for many of the reasons above, and as a DIYer, I like to design loudspeaker cabinets without factoring in, and perhaps being limited by, the relatively few production amplifier models available for powered loudspeakers.

We also prefer the built-in backup available in going with the outboard approach. In 40-plus years in the business, I’ve seen electronic failures happen with all kinds of gear (including amplifiers), and like that we can simply swap a loudspeaker over to another amp channel in case of failure.

Then To Now

Back in the day, power amplifiers were very large, heavy and relatively (by today’s standards) low-wattage mono or stereo units. Today’s models are far smaller and lighter in weight powerhouses that can also offer up to eight channels.

It’s not uncommon to see modern amplifiers rated at thousands of watts per channel. In contrast, our first amp rack consisted of three amplifiers that weighed more than 150 pounds (including rack and crossover) and offered a whopping total rated output of 900 watts, while the most recent amplifier we purchased delivers more than 1,000 watts per channel in a package that weighs less than 15 pounds.

Many manufacturers also offer processing capabilities in their amplifiers. This ranges from basic crossover function to advanced digital controllers with adjustable slopes, roll-offs and limiters with factory presets, storage of user settings, and networking that allows remote configuring of settings and monitoring performance.

A facet of amplifiers that I’ve found is confusing for a lot of folks are topology classes – class A, AB, D, H and other variations. Each topology has its own way of amplifying low-level signal as well as strengths and weaknesses. Some are more efficient, some produce less distortion, and so on. (For more information on topologies, go to ProSoundWeb, which provides several reference articles on the topic.)

Older designs may only be about 30 percent efficient in converting electricity into loudspeaker movement. The wasted energy generates heat, which was removed with heavy heatsinks and fans.

Newer switch-mode power supplies and amplifiers (a.k.a., Pulse Width Modulated or PWM for short) are 75 percent and more efficient in turning electricity into loudspeaker movement while producing less heat, which translates to smaller heatsinks and smaller fans or even no fans at all.

It all adds up to modern amplifiers that offer tons of power in compact units that produce little heat while being significantly lighter (and usually smaller) than previous models. With that in mind, let’s take a look around pro audio at the latest in audio power options.


Most recent from QSC are CXD-Q Series 8-channel network processing amplifiers designed specifically for integration with the company’s Q-SYS platform while also offering proprietary Flexible Amplifier Summing Technology (FAST), which enables the ability to combine up to four channels for higher output power.

They’re housed in a 2RU package and capable of providing up to 8,000 watts peak and 5,000 watts continuous with low-Z, with 70/100-volt direct drive available on all channels. They also include eight bi-directional GPIO connections that can be used for analog or digital inputs or outputs to/from the Q-SYS platform.

Earlier, QSC unveiled the GXD Series with a class D design as well as DSP that includes high- and low-pass filters (24 dB LR), 4-band parametric equalizer, signal alignment delay, and RMS/peak loudspeaker protection limiting.

Twenty preset “starting points” for select systems are also provided. A digital limiter prevents clipping, while protection is set by selecting the loudspeaker’s continuous power and impedance (4 ohms and 8 ohms), and then choosing a mild, medium or aggressive protection mode. The GXD 8 is specified as providing 800 watts per channel at 8 ohms (1,200 watts per channel at 4 ohms), and max total peak power of 4,500 watts.

Powersoft has long been an innovator in amplification, and the Ottocanali Series presents a range of 2RU, 8-channel models stated as capable of delivering up to 12,000 watts.

They implement two redundant universal switch mode power supplies with PFC (Power Factor Correction) and patented SRM (Smart Rails Management) technology that is designed to maximize efficiency and reduces power consumption.

The new Ottocanali DSP+D versions feature digital processing and support two redundant Dante streams. The DSP offers input and output delays, Butterworth, Linkwitz-Riley, and Bessel crossovers, high and low bandpass and bandstop filters, parametric EQ and limiters.

All versions in the series have switchable main and aux signal inputs per channel, alarms, and lo-Z and hi-Z output connections as well as mono-bridgeable channel pairs.

A recent release from Lab.gruppen, another long-time leader in the field, is the E Series, comprised of 1RU models available in both 2 and 4-channel versions with output of up to 600 watts per channel. E Series amplifiers also incorporate a new high-headroom universal power supply accepting any mains voltage from 70 to 265 volts at 50 or 60 Hz.

Lab.gruppen PLM+

A high storage capacity in the power supply prevents excessive draw on the mains inlet during repeated peak bursts, maintaining extra headroom on the supply rails for sustained maximum output with minimal distortion. The class D output stage is highly efficient (above 90 percent), with 2, 4, 8, 16-ohm operation as well as 70-volt output.

Meanwhile, the company’s flagship line, the PLM+ Series, demonstrates just how far amplifier technology has evolved.

For example, the PLM 20K44 combines a 4-input/4-output configuration and power output of up to 4,400 watts per channel at 4 ohms with a new Lake processing core module and Dante networked signal distribution.

Ashly Audio nXp

Ashly Audio has also pushed the envelop with the NX Series, made up of 36 different models, including 2 and 4-channel units with output ranging from 75 watts to 3,000 watts per channel to fit any application.

Meanwhile, nXe models add Ethernet control and can be specified with Dante, CobraNet and AES digital signal options to fit into existing networks. Even further, nXp models offer all nXe features plus Protea digital processing.

Protea software can remotely disable power and level controls for tamper-proof installations, and it hosts FIR filters and Voicing files provided by various loudspeaker manufacturers for further optimization.

The software also includes an auto mixer and feedback suppressor, EQ and crossover functions, dynamics processing with auto-ducker, time alignment, variable noise masking with RTC, and swept-load analysis with baseline logging function.

Crown Audio continues to develop and evolve several platforms, including the recent addition of two Dante-enabled amplifiers to the DCi Series.

Crown Audio DCi

The DCi 8|600DA offers 8 channels at up to 600 watts each, while the DCi 4|1250DA provides 4 channels, each capable of supplying up to 1,250 watts per channel.

Both models also support AES76 audio networking in addition to analog and Dante, while outputs can be configured for 2, 4 and 8 ohms as well as 70/100-volt operation.

Onboard processing includes an input router, input and output delay, input and output EQ, crossover, LevelMAX limiter, loudspeaker tunings, continuous load monitoring, and 20 user presets.

Linea Research 44M

Linea Research has unveiled the 48M (8 channels) and 44M Series (4 channels), all with built-in DSP and networked control. The 44M Series is available in models that develop between 1,500 and 5,000 watts per channel (up to 10,000 watts for a bridged pair), and they’re also specified as capable of delivering the same rated power into 2, 4, or 8-ohm loads or into 70/100-volt lines, configurable on a channel-by-channel basis.

All models include analog inputs and a built-in AES3 interface or an optional Dante module. DSP includes crossovers, limiters, bandpass filters and up to 12 layers of parameter overlays and groupings.

Crest Audio Pro-LITE

Long a noted name in amplification, Crest Audio has 8 recent models of lightweight amplifiers that comprise the Pro-LITE Series. All weigh in at under 15 pounds, with the most powerful stated as capable of delivering up to 9,600 watts.

Four of the models include DSP that includes Butterworth or Linkwitz-Riley crossovers, high and low bandpass filters, 5-band parametric EQ, horn EQ, Maxx Bass enhancement, driver or distance delay, and limiting. Users have the ability to store up to four presets.



About Craig

Craig Leerman
Craig Leerman

Senior Contributing Editor, ProSoundWeb & Live Sound International
Craig has worked in a wide range of roles in professional audio for more than 30 years in a dynamic career that encompasses touring, theater, live televised broadcast events and even concerts at the White House. Currently he owns and operates Tech Works, a regional production company that focuses on corporate events based in Reno.

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