The BasX A4 is a four-channel Class A/B power amplifier from Emotiva’s entry-level BasX range, designed to add clean multi-channel amplification to home cinema systems where the front channels are handled separately. It is rated at 100 watts RMS per channel into 8 ohms with all four channels driven simultaneously across the full 20 Hz to 20 kHz audio band, a figure Emotiva quotes under continuous, all-channels-driven conditions rather than single-channel or burst measurements, which is a more demanding and more honest benchmark.
Power Supply and Construction
The A4’s power supply is built around an oversized toroidal transformer in a linear topology. Toroidal transformers produce lower radiated magnetic flux than conventional EI-core designs, reducing interference with the amplifier’s own signal circuits. The linear supply avoids the high-frequency switching artefacts associated with switch-mode designs, which can degrade signal-to-noise performance in sensitive audio stages.
The output stage uses a Class A/B circuit laid out on double-sided FR4 PCBs with plated-through holes, a construction method that improves thermal and mechanical reliability compared to single-sided boards. The chassis is fabricated from heavy-gauge steel for rigidity and electromagnetic shielding, with a milled aluminium faceplate. Per-channel blue status LEDs indicate active operation; a front-panel switch can disable them for darkened listening environments.
Performance
THD+N is specified at less than 0.02% at rated power (A-weighted), and the signal-to-noise ratio exceeds 115 dB A-weighted referred to rated output into 8 ohms. The damping factor is greater than 500 at 8 ohms, which reflects a very low output impedance; a high damping factor gives the amplifier effective control over woofer excursion, improving bass definition and reducing port-tuning overhang. Frequency response extends from 10 Hz to 80 kHz at +0/–1.8 dB, with the power bandwidth flat to within ±0.02 dB across the 20 Hz to 20 kHz audio range.
The minimum recommended load impedance is 4 ohms per channel, accommodating one 4-ohm speaker or two 8-ohm speakers wired in parallel. Into 4 ohms with two channels driven, the A4 delivers 175 watts RMS per channel, giving useful headroom for lower-impedance surround or height speakers.
Connectivity
Each of the four channels has a dedicated unbalanced RCA input. Speaker outputs use audiophile-grade five-way binding posts, accepting banana plugs, spade lugs, or bare wire. A trigger input accepts 5–12 V AC or DC, allowing the amplifier to be powered on and off automatically by an AV processor or preamplifier; a push-button standby is also available. The unit operates on universal mains voltage, requiring no modification for UK use.