UK-based Linea Research, for years a designer and manufacturer of OEM power amplifiers with sophisticated digital signal processing for several top pro audio companies, has now launched products under its own name. The Linea line includes 8- and 4-channel DSP amplifiers for both touring and installation applications, as well as a digital system controller.
Here we’re going to take a look at the 44M20, a 4-channel DSP amplifier for live sound/touring. It’s housed in a 2RU package specified as delivering (per channel) 1,500 watts at 8 ohms, 3,000 watts at 4 ohms, and 5,000 watts at 2 ohms, all channels driven. The class D amplifier designed has a stated frequency response of 7 Hz – 30 kHz (-2.5 dB) at 4 ohms, low inter-channel crosstalk (better than -85 dB at 1 kHz), and a low total harmonic distortion rating of <0.05 percent (typical at 4 ohms with a 1 kHz signal). Analog and AES inputs are standard, with Dante inputs an option. (The unit provided for this evaluation had all three.) It's only 14 inches deep behind the rack ears and weighs in at a scant 27.5 pounds. Note that while light in weight, if the amp is mounted in a mobile rack, it's important that the rear is supported with the rear rack mounting kit. The front panel offers input and output meters as well as individual channel output mute buttons. A nicely sized LCD screen occupies the middle, flanked by six menu buttons and two rotary encoders. The bottom is dominated by a large air inlet covered with an intake filter that's easily removed for cleaning. The rear panel provides all I/O, including Neutrik SpeakON connectors for loudspeaker outputs. Each amplifier channel has an XLR input and output, and there's also AES I/O. Dante primary and secondary ports and a RJ45 port for computer control are located next to a recessed software reset button and Phoenix connector that can relay fault information. For power, a 32A Neutrik PowerCon-type locking AC connector is provided. All Linea models are designed to operate on 50/60 Hz AC power, and the power supply automatically configures itself for either 115- or 230-volt nominal voltage at turn on.
The processing offers a new way of ordering and grouping channels called Drive Modules that provide a more loudspeaker-centric approach to controlling, designing and recalling configurations. A Drive Module consists of different “blocks” of DSP, one for the input and several for the outputs that are used for control and monitoring of the associated loudspeakers.
Further, presets can be broken apart into components, allowing any output to be used for any loudspeaker or even specific transducer in a system. For ease of use, Overlay Groups allow various input parameters to be adjusted in all modules in a group while maintaining independent parameter values across each group. For example, EQ could be adjusted for every group without having to access each channel’s Drive Module.
In addition to gain, EQ, and delay parameters, the software also provides access to a new type of crossover filtering called LIR. This response filtering results in a linear phase crossover that has a constant delay regardless of frequency. The shape of the LIR filter is quite similar to a 4th order or 24 dB/octave Linkwitz-Riley filter, and the factory states it maintains zero phase difference between the adjacent bands across the crossover region to keep the polar response “rock steady.”
Control of the 44M20 is provided by the System Engineer PC application that offers features such as flexible management of presets and overlay grouping of mutes, gains, delays, and EQ across an entire sound system. In addition to the DSP, each output can be optimized to drive either a low impedance load (8, 4 or 2 ohms) or a constant voltage setting (25-, 70- and 100-volt line) in the output menu.