This range of four-channel power amplifiers is intended for commercial and industrial public-address and sound-reinforcement applications where unquestionable long-term reliability is the primary consideration. The three models in the range, offer four channels of 120W, 240W and 400W output; pairs of channels may be operated in bridge mode. The steel 2U chassis has variable-speed, forced-air cooling while the protection circuitry includes clip-limiting and switch-on delay, together with DC, thermal, short-circuit and reactive load protection. The inputs are line-level and electronically balanced, VCA circuitry is provided for remote level control and an optional web monitor card permits monitoring of the amplifier's performance, via a standard Ethernet connection, and if connected to the internet, world-wide, even on a mobile phone.
The amplifiers are designed to deliver their full rated power into loads down to 4 ohms for long periods of time, while bridge mode uses a pair of channels to provide double the normal power into a load of 8 ohms. As well as theatres, leisure centres and other major venues, they are also aimed at applications in airport terminals, railways stations and similar large public spaces.
The substantial front panel, constructed from a cast aluminium facia sandwiched with a steel backing-plate, is dominated by two air-intakes for the variable-speed DC cooling fans. In the centre an inset panel houses LED indicators showing power status, signal presence, signal peak and protection system active for each of the four channels. A large rocker switch turns the amplifier on and off. Two protruding lugs provide protection should the amplifier be placed on the front panel, perhaps during installation.
The rear panel also has two grilles, for air to flow out past the internal heat-sinks. Power is connected by an IEC inlet, which has an adjacent circuit breaker. There are four areas, each for a single channel, each having controls and connectors as follows. The input is a 3-pole, detachable, terminal connectors; Euroblock or 'Phoenix' style. The level control is recessed and screwdriver-operated. A larger 3-pole Euroblock connector provides the connection for remote level control. A switch switches the hi-pass filter in and out of circuit. The controls for channel 2 and channel 4 also have bridge switches, connecting channels 2 and four to channels 1 and 3 respectively. Channels 2 and 3 also have a switch to select the input from channel 1, rather than channels 2 and 3, so that all three could be driven from a single input. Channel four offers the choice of the channel-2 input or the channel-4 input. Two 4-pole Euroblock connectors provide the loudspeaker connections. A blanking panel covers the aperture where the optional VTX-WM1 Web Monitor Card may be fitted.
Specifications
Included accessories: AC power lead, Set of mating screw-terminal connectors, push-in feet, manual.
Optional accessories: VTX-WM1 surveillance card, RL-1 remote control, CXL-100T line driver transformer.
This may be retro-fitted to Cloud VTX Series power amplifiers, making it possible for a remote user to monitor the performance and settings of the amplifier over a local network or the internet using any personal computer, PDA or smartphone and a normal internet browser application. No dedicated software application or hardware is necessary. The system can also be configured to generate an email report, optionally formatted for SMS text forwarding, if the monitor card detects a fault condition. As well as checking the integrity of the amplifier, the VTX-WM1 generates a test signal for the load impedance test, at one or more user-definable frequencies.
The card simply slots into the pre-prepared aperture on the rear of the amplifier and some internal jumpers are changed. After powering up the amplifier, the installer must log on to the web-server in the amplifier, much in the way that one logs into the configuration page on a router, to set the required IP address. These can either be on the local internal subnet, which will give access to the amplifier by local computers, or fixed IP addresses provided by the user's ISP, thus giving access anywhere from anywhere on the internet. Alternatively remote access may be engineered by forwarding different ports to the different amplifiers, using a local machine as an intermediary with a Remote Terminal Services session or by use of a VPN. The card does not support DHCP. Up to 254 VTZ-WM1 cards may be deployed in one subnet.
Network connection status, the settings of all amplifier rear-panel switches and gain controls, protection circuitry activity, internal temperature, power status and input signal level for each channel are monitored by the card. Fan operation and remote volume control settings (if fitted) are also confirmed. It confirms all user-definable control settings and checks load impedance on demand, or at scheduled times using user-defined frequency. A real-time clock provides for event logging, at a user-definable polling interval, with automatic email or SMS text alert on pre-defined fault conditions. Battery back up provides for messaging should the amplifier power down or even expire, in which case it will e-mail the final settings and events.
A load impedance test is available to check the integrity of each channel's loudspeaker(s) and cabling. This test may be run either manually, initiated from the GUI as required, or automatically at pre-determined times and intervals, usually during periods of non-occupancy. The frequency used for the impedance test is also programmable between 60kHz and 20kHz to allow the installer to select a frequency that is suitable for the different drivers and to avoid speaker resonances, causing inaccurate readings.
The web browser GUI has a set of tabbed pages, which report the details and performance of all the amplifiers on the network. A password protected 'Housekeeping' page is provided which allows site-wide details of the installation to be entered. This page also allows the load impedance test parameters, IP addresses and other system settings to be configured. A real-time clock runs independently of the amplifier power supply and an event log is maintained, which can be inspected as required for investigative purposes in the event of system problems.
Tone generator: 40dB below maximum amplifier output, injected post level-controls, other channels muted. Frequency range: 60Hz - 20kHz, 1/3-octave steps. Signal detector: -30 to +10dBu sensitivity, 20Hz - 20kHz. Ethernet connection: 100 Base T.