The BasX A4 sits within Emotiva's BasX range — a series designed to bring the company's engineering principles to a lower price point without compromising core performance. The A4 is a four-channel Class A/B power amplifier intended primarily for home cinema use, providing clean, capable amplification for surround, height, or zone speakers in systems where the front channels are already served by a dedicated stereo or AV amplifier. Rated at 100 watts RMS per channel into 8 ohms with all four channels driven simultaneously, it is one of the more honest measurements in its class, as many manufacturers quote single-channel figures at 1 kHz only.
Construction
The A4 is built around a heavy-duty linear power supply centred on an oversized toroidal transformer. This topology is deliberately chosen over a switched-mode supply: toroidal transformers offer lower radiated magnetic flux, which reduces interference with sensitive audio circuitry, and a linear supply avoids the high-frequency switching noise that can affect signal quality. The amplifier section uses a carefully designed, short signal-path Class A/B output stage on double-sided FR4 circuit boards with plated-through holes — a construction method that improves solder joint reliability and trace integrity compared to single-sided boards.
The chassis is fabricated from heavy steel for rigidity and shielding, with a milled aluminium faceplate that lends a clean, purposeful appearance suited to rack mounting. The overall build follows a philosophy of allocating budget to electrical performance rather than cosmetic elaboration.
Performance
Total harmonic distortion plus noise (THD+N) is specified at less than 0.02% at rated power, and the signal-to-noise ratio exceeds 115 dB A-weighted — figures that reflect the benefit of the linear power supply and the short signal path. The damping factor is greater than 500 at 8 ohms, which indicates a very low output impedance relative to the speaker load; a high damping factor gives the amplifier greater control over woofer cone movement, reducing overhang and improving bass definition.
Frequency response extends from 10 Hz to 80 kHz (–1.8 dB), with power bandwidth flat to within ±0.02 dB across the full 20 Hz–20 kHz audio band. The amplifier accepts an input sensitivity of 1.2 V for rated output, with a gain of 29 dB and an input impedance of 27 kilohms — compatible with the output stages of standard AV processors and preamplifiers.
Connectivity and Integration
Each channel is provided with an unbalanced RCA input. Speaker connections are made via five-way binding posts that accept banana plugs, spade lugs, or bare wire. A 12 V trigger input allows the amplifier to be switched on and off automatically by an AV processor or preamplifier, with a corresponding trigger output to chain further components. The unit operates on universal voltage (115 V or 230 V, 50/60 Hz), making it straightforward to deploy in the UK without modification.
Specifications
| Channels | 4 |
| Power output (all channels, 8 Ω) | 100 W RMS per channel (20 Hz–20 kHz, THD < 0.1%) |
| Power output (all channels, 4 Ω) | 130 W RMS per channel (1 kHz, THD < 1%) |
| Power output (two channels, 8 Ω) | 100 W RMS per channel |
| Power output (two channels, 4 Ω) | 175 W RMS per channel |
| THD+N | < 0.02% (A-weighted, ref. rated power) |
| Signal-to-noise ratio | > 115 dB (A-weighted, 8 Ω, ref. rated power) |
| Frequency response | 10 Hz–80 kHz (+0/–1.8 dB) |
| Power bandwidth (8 Ω) | 20 Hz–20 kHz (±0.02 dB) |
| Damping factor (8 Ω) | > 500 |
| Input sensitivity | 1.2 V |
| Gain | 29 dB |
| Input impedance | 27 kΩ |
| Inputs | 4 × unbalanced RCA |
| Speaker outputs | 4 × five-way binding posts |
| Trigger | 12 V trigger input and output |
| Amplifier class | Class A/B |
| Power supply | Linear, toroidal transformer |
| Mains voltage | Universal (115 V / 230 V, 50/60 Hz) |
| Dimensions (W × H × D) | 432 mm × 102 mm × 394 mm (17″ × 4″ × 15½″) |
| Weight | 11.8 kg (26 lb) |
| Warranty | 3 years |
