The Anthem STR Power Amplifier is built for systems that need more than a conventional stereo power stage. Its combination of two toroidal transformers, a fully dual-mono circuit layout, sixteen bipolar output devices per channel, and output ratings extending to 800 watts per channel into two ohms points to an amplifier designed around demanding loudspeakers and wide variations in load. Yet raw output is only part of its appeal. Anthem has also addressed protection, automation, setup, and system integration—areas that become increasingly important when a large power amplifier is used as the foundation of a serious stereo or combined music-and-cinema installation.
A fully dual-mono power architecture
At the center of the STR Power Amplifier are two substantial toroidal transformers supporting a fully dual-mono design. In practical terms, the left and right channels have dedicated power resources rather than relying on a single shared transformer. This approach is particularly appropriate for a high-output stereo amplifier because it gives each channel a more independent electrical foundation.
The architecture also reflects the STR’s intended role as a long-term system component rather than a compact convenience amplifier. It measures 17.2 x 43.2 x 47 centimeters and weighs 27.3 kilograms without packaging. Those figures should be considered when selecting furniture, rack space, ventilation, and shelf support. The size and weight are directly relevant to installation, especially in systems where the amplifier will be placed near other heat-producing electronics.
Class AB output for challenging loudspeaker loads
The STR is specified to produce 400 watts per channel into eight ohms, 600 watts into four ohms, and as much as 800 watts into two ohms across the 20 Hz to 20 kHz range at less than 1% total harmonic distortion. The increasing output into progressively lower impedances is an important part of the amplifier’s identity. Loudspeaker impedance can vary substantially with frequency, and models presenting low-impedance sections place greater current demands on an amplifier.
Each channel uses sixteen bipolar output devices in a Class AB configuration. Distributing the output stage across multiple devices is intended to support high current delivery while maintaining linear operation and dependable performance. Prospective owners planning to exploit the amplifier’s two-ohm capability should ensure that speaker terminals, cables, power provision, ventilation, and the loudspeakers themselves are suitable for the potential current and output involved.
Other published figures provide further context. Anthem specifies 0.0007% total harmonic distortion at 400 watts and 1 kHz, a frequency-response deviation of ±0.1 dB from 20 Hz to 20 kHz, a slew rate of 30 V/µs, and a damping factor of 360 from 20 Hz to 1 kHz. These are laboratory specifications rather than listening conclusions, but they clarify the engineering priorities behind the design: wide bandwidth, low measured distortion, and controlled high-power operation.
An unconventional low-noise input stage
Anthem’s input and output topology departs from a traditional differential input-stage arrangement. The circuit employs eight low-noise bipolar input devices in a cascaded-feedback configuration with an active load. The stated goals are lower distortion, improved linearity, and greater bandwidth.
Critical transistors are hand-selected and matched, a production choice intended to reduce variation between devices in sensitive parts of the circuit. Combined with the extensive bipolar output stage, this indicates that the STR’s performance targets depend not only on large transformers and headline power ratings, but also on close control of small-signal behavior before the signal reaches the output section.
The specifications account for both unbalanced RCA and balanced XLR connections, with respective input impedances of 10 kilohms and 15 kilohms. Input sensitivity is listed as 2.1 volts RMS for 400 watts into eight ohms. That information is useful when matching the STR with a preamplifier or processor, since the upstream component needs to supply an appropriate output level and operate comfortably into the stated input impedance.
Advanced monitoring without conventional onboard fuses
High-output amplification requires protection, but protective systems must also avoid intruding unnecessarily during normal use. The STR operates without onboard fuses and instead employs Anthem’s proprietary Advanced Load Monitoring, or ALM, technology. ALM continuously observes internal temperature, current, and voltage to help preserve system integrity.
This active approach allows the amplifier to monitor several operating conditions rather than depending only on a conventional fuse. For an owner, the attraction is not simply protection in isolation; it is protection designed as an integrated part of the amplifier’s operation. That is especially relevant when driving low-impedance loudspeakers or using the amplifier at elevated levels, where thermal and current conditions can change quickly.
Power consumption is specified at 0.31 watts in standby and 65 watts at idle. Anthem lists consumption of 150 to 300 watts at typical levels and 600 to 1,100 watts at high levels. These figures help owners plan placement and electrical requirements while setting realistic expectations for a large Class AB design.
A front display that makes status visible
Large power amplifiers are often intentionally minimal, but the STR adds a front-panel graphic display. It presents power levels and status indicators, making basic operating information visible without requiring access to the rear panel or another component.
That feature is useful in more complex systems because it gives the owner immediate confirmation of amplifier status. It also helps with setup and navigation. While the display does not alter the underlying amplification, it makes a technically ambitious component easier to live with and distinguishes the STR from power amplifiers that provide little more than a standby light.
Flexible power control for stereo and cinema systems
The STR includes a soft-start mechanism and four options for controlling power-on and power-off behavior. Soft start is a sensible inclusion in an amplifier with two substantial transformers because it manages the transition from standby rather than applying the full startup demand abruptly.
Its control options include trigger operation and input-signal sensing, which can be combined so that routine switching does not require manual use of the front panel. In a straightforward stereo system, this allows the amplifier to follow the operation of a compatible preamplifier. It is even more relevant in an integrated music and home theater installation, where several components may need to wake and shut down together.
Anthem specifically positions the STR for use with a preamplifier operating in bypass mode alongside a surround processor. In such a configuration, the same power amplifier and front loudspeakers can serve a dedicated two-channel signal path and the front channels of a cinema system. Automated trigger and signal controls reduce friction when moving between those roles. The STR can naturally be paired with Anthem’s matching STR Preamplifier, but its RCA and XLR input provisions also make broader system matching possible, provided electrical compatibility is observed.
Who the Anthem STR Power Amplifier is for
The STR is most suitable for an owner assembling a high-output separates system around a dedicated preamplifier, particularly when the loudspeakers have low-impedance regions or benefit from substantial amplifier headroom. Its dual-mono construction, two-ohm rating, active monitoring, and extensive output stage also make it relevant to listeners who want one amplifier to remain useful through future loudspeaker changes.
It is equally well suited to a hybrid stereo and home theater installation. Bypass-based integration, trigger control, and signal-sensitive operation allow it to support music playback and cinema duties without requiring repeated manual switching.
It will be less appropriate where space, weight, heat, or electricity consumption are primary constraints. At 27.3 kilograms and nearly 47 centimeters deep, it requires a suitably strong, ventilated location. Owners of efficient loudspeakers in smaller rooms may not need its available output, while anyone seeking a single-box integrated amplifier will still need a separate preamplifier or processor. The STR’s strengths are therefore most relevant when power, load capability, system flexibility, and separates-based construction take priority over compactness.
Conclusion
The Anthem STR Power Amplifier combines several documented qualities that matter in an ambitious separates system: fully dual-mono construction with two toroidal transformers, a sixteen-device-per-channel Class AB output stage, ratings from 400 watts into eight ohms to 800 watts into two ohms, and continuously operating ALM protection. Its graphic display, soft start, multiple power-control options, and support for both stereo and home theater integration make the substantial hardware more manageable in daily use. Designed and crafted in Canada, it is aimed most clearly at owners of demanding loudspeakers and those building a powerful two-channel system that may also serve as the front end of a modern cinema installation.