Technology Showcase: Networked Power Amplifiers
Mar 1, 2007 12:00 PM, By Bennett Liles
Advances in networking unlock amplifier feature potential.
One day, commercial sound distribution moved beyond analog audio DAs and expanded into AES/EBU. That was, at the time, considered revolutionary. Now that uncompressed digital audio has followed packetized computer data into Ethernet networks, a new era in power amplifiers has emerged.
In the past, power amps were often necessarily big, heavy, and hot. They demanded a huge amount of rack space, and their output lines suffered high losses, requiring the shortest possible cable runs to speakers. These simple brutes normally had a power switch, a couple of level knobs, and a stereo/mono bridging switch. They either shook the speakers or smoked and stopped. Any more sophisticated audio signal refinements were performed elsewhere.
Then, wonderful things began to happen. Along with the emergence of Ethernet audio distribution came new amplifier circuit classes, mixed high- and low-impedance outputs, digital signal processing, and multichannel designs that allowed power amps to shrink in size while growing in feature sets. Still, some of the basic properties involved in power amplifier operation suggest that they should ideally be located at a distance from the central sound control point. This necessity and the new range of internal processing options have driven the development of networked power amps. In this new arena, there are a few models that allow Ethernet audio to input directly, but most of the features presently available require networked monitoring and control.
Along with responding to power on and off, multichannel level control, equalization, delay, and a plethora of other DSP commands from operators, networked power amps can now report temperature, power glitches, fan speed, output circuit interruptions, and a host of other conditions, all while returning the audio signal seen at their inputs over the same networked cable. Some manufacturers offer this distribution and control built-in, while others market these features as optional with the installation of a plug-in module with RJ-45 or sub-D connectors.
Since many installations will see multiple amplifiers mounted into the same rack, there are also products that accept the network audio via CobraNet or a proprietary protocol. These products terminate the Ethernet line in a rack module that carries analog line level signals to the amp inputs and runs control signals the short distance from that unit to the amplifiers by way of RS-485 on a sub-D connection. Other designs use Ethernet lines for the audio and run the bidirectional control and monitoring lines on serial connections all the way to the control point. This article will examine those products that either combine control and monitoring functions on network lines, or use a separate serial remote feature for all or part of the cable run. Some of these units mount directly into the amplifier chassis and others occupy separate enclosures but are marketed specifically as amplifier control units.
STATE OF DEVELOPMENT
Control and monitoring are typically set up through a software application on a computer connected to the nearest networked unit by serial or USB, and carried along the network by means of a proprietary protocol specialized for the physical scheme used by the amplifier manufacturer. A testament to the young stage of development in this field lies in the number of different names and feature sets for the control applications and for the transmission protocols used. Euroblock connectors are also common, and a few companies have even combined the control and multichannel audio on DB-25 connectors in an effort to save panel space. Many models also incorporate local front-panel LEDs for anything from simple power indication to a range of multi-colored indicators for more sophisticated parameter display and diagnostics. This examination offers a good opportunity to snapshot the current state of development in this rapidly evolving field.
The PE Series (Protea Enabled) amplifiers from Ashly are a prime example of control and monitoring over Ethernet while using analog inputs for program sound. These signals use Neutrik XLR/TRS combo and six-pin Euroblock connectors with male XLR loop-through connections for additional amps. Locking Neutrik Speakon connectors attach output lines and share the rear panel with switches for clip limiter, high-pass filters, input signal ground lifter, input gain setting, and operating mode.
Protection features include Safe Operating Area for power transistors, over-current protection, DC current protection, thermal protection, mains failure, and fuse protection. The front panel sports several LEDs that provide a range of performance monitoring functions, including status indicators for power, standby, operating mode, and COM link. Also indicated are output voltage, clipping, and fault warnings.
Using the Protea software, remote control of input attenuation, power on/off, channel mute, and polarity, along with monitoring output voltage and current, clipping, and temperature is easy. The PE-3800 offers 1900W into 4V in stereo mode and 3800W into 8V running in bridged mono. An optional Protea DSP card can provide 32-bit/96kHz processing with analog and AES3 inputs and two additional processed output channels. The current list price for the PE-3800 is $3,100.
Camco's Tecton series amplifiers typify the range of control and networking options available with add-on UCA (UniversalControllerAmp) modules. The Tecton 38.4, for instance, can use the Camco UCA-ES module to provide 48kHz EtherSound inputs on Neutrik EtherCon RJ-45 connectors with configuration and control through the free WinCai software application. The module enables users to operate 30 parametric EQs, delays up to two seconds in 21 µsec intervals, shelving filters with visual settings, crossovers, and two independent limiters on each channel with adjustable threshold, ratio, attack, hold and release, and dynamic resource management.
The Ethernet audio input modules enable control and audio input on the same Cat-5 cable. The Tecton series amplifiers offer three operating modes — stereo, bridged mono, and parallel mono — output current monitoring, input sensitivity selector, switchable peak limiter, selectable subsonic filter, ground lifter, DC protection, over-voltage protection, and front-panel LEDs for operating mode, clipping, signal and output current indications. The Tecton 38.4 pumps 1136W into 8V in stereo mode, 3000W into 4V in mono bridged, and 3000W into 1V in parallel mono.
The Ci series power amplifiers from Crest Audio provide output from 4V to 70V, and with the addition of the Nx CobraNet-8 module, can be monitored and controlled in a network using the NexSys 4, MediaMatrix MWare, or NWare software applications for multiple points of control.
These amps also feature a gain control voltage connection on each channel for remote gain adjustments. Local level controls are on the rear panel, and all the inputs and outputs are on Phoenix connectors. The Ci 30×4 and Ci 20×8 models contain a rear bay into which the Nx CobraNet-8 module slides to enable the amplifier to perform all NexSys and DSP functions, along with CobraNet I/O, on a single Cat-5 line. Speaker management and channel routing, EQ, delay, compression/limiting, and crossover control are all available, and monitoring includes active clip limiting, instantaneous gain modulation, input/output gain levels, DC, thermal protection, fault, mute, and Ethernet status. The Ci 20×8 is rated at 150W into 4V for eight output channels, 220W per channel into 8V, 200W at 70V, 300W per channel at 8V bridged and 400W per channel at 140V bridged.
The Crown CTs 4200USP/CN and 8200USP/CN amplifiers with PIP (Programmable Input Processor) input modules can connect to Crown's HiQnet for network monitoring and control with System Architect software, along with a CobraNet audio distribution network for sound input, all over the same Ethernet Cat-5 cable.
The input processor's DSP capabilities include audio routing, faders, meters, polarity and mute, input compressors, filters, delays, multimode output limiters, error reporting, and load monitoring. Built-in noise and sine wave generators aid the acoustic calibration tests. The aux connector is configurable to function in aux input, aux output, and listen bus for monitoring. The RJ-45 network connectors are duplicated for automatically switched backup in case of a network connection problem. Ten user-selectable presets store a multi-parameter setup for instant recall with a reset/preset switch. The CTs 8200USP/CN outputs 175W per channel into 4V with eight channels driven, 230W per channel into 4V with one channel driven and 350W per channel into 8V in bridged mono mode with four channel pairs driven. The CTs 8200 without options can be found for slightly more than $2,000.
The Precision series P3000RL from Electro-Voice can be accessed through one or more PCs running IRIS-Net software (Intelligent Remote and Integrated Supervision Network) for central control of up to 100 amplifiers via the Can-Bus, a balanced serial interface for command and data transmission. The same bus or line network cabling also carries the balanced return audio signal for monitoring the power amp inputs and outputs.
Each P3000RL features a Can-Bus LED indicator to note any network signal activity and the hexadecimal address of each amplifier in the network is set with two rotary switches. The amp is rated at 1800W continuous power into 2V and 850W into 8V. Internal protection circuits include thermal overload, short circuit, DC/HF protection, and inrush current limiter. Remote-controlled signal processing includes 24 filters, five delays, two compressors, and two limiters. Speakers connect with Neutrik Speakon NL4 connectors. Network control includes parameters such as operation mode, temperature, pilot tone, protection mode status, impedance of connected speaker system, output current, and output voltage. The MSRP for the P3000RL is $3,250.
The new Lab.gruppen FP+ series is billed as a line of tough, touring-power amplifiers with high power density through Class TD output stages in 2- and 4-channel versions with NomadLink network monitoring and control modules included as standard hardware. The FP 13000 delivers 6500W per channel into two channels at 2V and stands only 2RU high.
Adjustments include selectable gain from 23dB to 44dB, scalable voltage peak limiter, and bridge-mode selection. Once the NLB 60E NomadLink Bridge and network controller is connected, the amplifier DeviceControl software may be used to monitor key amplifier parameters and control power on/off, mute, and solo channels. Rear-panel connections include input XLRs, output binding posts, NomadLink RJ-45s, power on/off, and remote enable on/off. The front panel bears level indicators for each channel, bridge mode and clipping indicators, VHF and temperature warning lights, power indicator, and NomadLink light.
The NLB 60E NomadLink/Ethernet Bridge enables networked control and monitoring of dozens of FP+ series amplifiers in a closed-loop, daisy-chained network topology in which amplifiers may be grouped into subnets and operated in groups. Both voltage and contact closure-sensing general-purpose inputs are available. The MSRP on the FP 13000 is $6,645.
The MC1250 from MC2 represents a serial control method with Class AB bipolar program signal outputs with a floating drive stage. The bidirectional remote control uses a standard RS-485 protocol with attachment by a nine-pin D-sub on the rear panel, which also features the linked input XLRs on each channel, a stereo/mono bridged mode switch, a 2V/4V load selector switch, and 4mm binding posts for the output connections.
The attractive front panel has an inset area with peak level meters indicating headroom, which double as level control indicators while adjustments are being made; power rocker switch with power light; bridged-mode indicator; DC and short-circuit indicators; user-selectable clip limiter; and mute switches that initiate a gentle fade-up when pushed and released to avoid sudden sound blasts to the speakers. This inrush protection is also evident in the normal power-up sequence, which then fades up the gain to the previous setting. If a short occurs on the output, the short protection kicks in and then clears itself automatically when the short is eliminated.
In stereo mode, the MC1250 can put 1800W into 2V, and in mono bridged operation is rated at 3600W into 4V. The MC1250 can be found for less than $4,000.
The Digam L series from Powersoft was introduced in 2- and 4-channel versions to offer sophisticated features in the lightest and smallest possible package. This line of amplifiers has shrunk the depth and reduced the height to 1RU. The serial remote control and monitoring option is implemented through RS-485 on a rear-panel RJ-45 connector.
The remote/monitoring system is composed of the PowerControl Manager software, the PowerControl Hub unit, and the PowerControl amplifier internal board for control of up to 99 units from a single PC. Input signals, output voltages, internal temperature, clip and fault warnings, and total working hours can be monitored. Presets enable level changes and mutes to be made in groups, and email notices can be programmed to warn of anomalies. All such occurrences may be stored on PCM memory.
Another option enables onboard DSP functions. Safety features include clip limiters, DC, VHF, and thermal protection, along with AC voltage sensing and auto shutdown. The front panel includes LED level indicator, temperature and ready lights, and gain control knobs. The LQ2804 can provide 700W into 4V, 360W into 8V, and 1400W into 8V in bridged mono mode.
Among the wide range of amplifiers offered by QSC Audio is the CX 8-channel series, which features four HD-15 rear-panel data ports (one per channel pair) for remote amplifier management and diagnostics or DSP by computer through the company's QSControl system. Control signals are sent through an Ethernet switch to the QSC16a amplifier network monitor and then to the HD-15 ports on the amplifiers.
Typical of this line is the CX168, which provides 90W per channel at 8V and 130W at 4V in a 2RU frame only 14in. deep. The bridgeable channel pairs allow configuration as a 5-, 6-, 7-, or 8-channel unit. One interesting and useful feature on these amps is an integrated security cover over detented gain controls to prevent tampering with volume levels. With the cover installed, the front indicators are still visible, but the level controls are hidden.
Protection features include DC current, thermal overload, infrasonic/ultrasonic, short circuits, and active AC inrush limiting. Inputs and outputs interface on detachable Phoenix-style connectors. Front-panel LED indicators show signal level, clip status, and bridged or parallel operation mode, while the rear panel has one connector block per channel pair with clip limiter enable, LF on/off, and bridged/parallel mode selection. Fan speeds vary automatically with temperature sensing and run at the lowest safe speed to minimize noise. At press time, the MSRP for the CX168 was $1,760.
One notable example of an Ethernet network amplifier controller is the Yamaha ACU16-C amp control unit with 24-bit D/A conversion of up to 16 CobraNet audio channels for up to eight 2-channel power amplifiers at a dynamic range up to 110dB.
The analog output is run to the amplifier inputs on 2-channel Euroblock connectors while the monitoring and control is interfaced through RS-485 on a rear-panel RJ-45 terminal. The control computer attaches to the unit with either USB or RS-232C ports. Up to 16 ACU16-Cs can be used on a single CobraNet network. Monitoring and control for up to 32 PC-N series amplifiers per control unit is possible with the Yamaha NetworkAmp Manager software included with the product and running on a Windows PC.
Conditions including protection circuit on, heat sink temperature, power on, standby, attenuation, phase, muting, and speaker failure are noted, time-stamped, and written to a log file. For dependable network connection, primary and secondary Ethernet ports are provided. The front panel includes a USB mini port and a unit ID rotary switch, along with link and error lights. A conductor light indicates if the unit is functioning as the CobraNet wordclock master and conductor for the network. Also displayed is the power switch. The ACU16-C can be found for less than $3,000.
At this stage of the technology, the specific layout for amplifier monitoring, control, and audio distribution can take any form, from direct Ethernet distribution and control or separate network audio distribution, to serial control/monitoring directly from a central location or an intermediate amplifier distribution and/or control unit. The exact plan used will be determined by careful consideration about the physical venue, the budget, and the necessary capacity for expansion.
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Bennett Liles is a freelance television production engineer and AV technician in the Atlanta area. He specializes in government video production, distance learning, and videoconferencing.
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