The Arcam Radia A25+ amplifier offers the best performance and sound in the Arcam Radia line, surpassing the Arcam A5+ and Arcam A15+. Unlike its smaller brethren, which operate in Class A/B amplification, the A25+ is a Class G amplifier with 100 watts per channel. This design allows the amplifier to operate in pure Class A until it reaches 20 watts per channel, then transitions to Class AB. Massive, backlit knobs add a touch of luxury to the anodized aluminum enclosure, and a compact remote control is included. A headphone output (mini-jack) is located on the front panel.
Class G is a derivative of class A/B, but before we explain, let's first look at other amplifier classes. Class A is used for low-power systems. Many valve amplifiers are class A, with a single output device. This amplifies the entire audio waveform. Class A sounds the best, but it is very inefficient and requires a large power supply. As a result, class B was developed, which uses two or more output devices. Each output transistor processes half of the audio waveform. This makes it more efficient, but can suffer from crossover distortion. This led to the development of class A/B, where class A is used at low power levels, and class B gradually switches on at higher volumes.
Class G is similar to Class A/B, except it improves amplifier efficiency by using multiple power rails, thereby optimizing the power supply. Class G uses at least two different rails, and each higher-voltage rail is activated as the volume increases. The advantage is increased efficiency with higher output power. You'll experience a smoother, more dynamic, and overall much more musical sound than other amplifier designs.
The Arcam A25+ amplifier features integrated two-way Bluetooth, which utilizes the latest 24-bit HD aptX 5.4 codec for the best possible sound. This allows you to stream music from your smartphone, tablet, or other Bluetooth-enabled device. You can also connect to Bluetooth headphones, a useful feature for attentive evening listening.
The built-in DAC features a high-quality ESS ES9018 DAC chipset, one of the best-sounding DACs available today. Three digital inputs are included alongside three standard line-level inputs, allowing you to enjoy the best sound from a wide range of music sources using your chosen input—either directly at line level or taking advantage of the excellent built-in DAC via the digital input.
Arcam hasn't forgotten vinyl lovers, and the Arcam A25+ integrated amplifier features a high-quality phono preamplifier designed for millimeter-amplifier cartridges. There are two types of cartridges: moving magnet (MM) and moving coil (MC). The latter has less power and requires a separate phono stage, which is a possible upgrade.
Differences between the Arcam A and A+ amplifier models:
New from ARCAM are the A5+, A15+, and A25+—a trio of integrated amplifiers based on the previous A5, A15, and A25 models, featuring improved circuitry, upgraded components, and intelligent power management, delivering enhanced performance. Each amplifier utilizes ARCAM's latest Bluetooth 5.4 platform, with support for Snapdragon Sound (AptX Lossless) for bit-perfect CD-quality streaming, LE Audio, and Auracast, enabling one-to-many wireless playback without the need for pairing.
Both the A15+ and A25+ now feature HDMI eARC, an improvement over their predecessors. The Class-G-based A25+ also features a precision-crafted glass front panel for a sharper, brighter image, complementing the ST25's streaming capabilities. It receives the most significant upgrade of the trio: a new transformer with separate windings for the digital and DAC circuits, dual linear regulation in the analog power supplies, and further improvements to power and line filtering for lower impedance and improved overall audio clarity.
Upgraded transformers in the A15+ and A25+ further reduce unwanted currents within the chassis, while the A5+ benefits from component improvements that reduce PCB interference and lower power supply impedance. The A25+ also incorporates an ESS9018 DAC dedicated to the SPDIF inputs, further enhancing audio quality.
Noise reduction remains a key focus of the engineering. By selectively disabling unused components, overall noise levels are significantly reduced. For example, the DAC board is powered down when the analog input is used; Bluetooth and HDMI modules are powered down when auto-sensing is disabled; and the trigger input is disabled when no cable is connected—all of these measures contribute to a cleaner power supply environment.
Arcam A25+ Specifications
- Continuous output power: (0.5% THD), per channel into 8 ohms 100W
- Harmonic distortion, 80% power, 8 ohms at 1 kHz 0.002%
- Signal-to-noise ratio 110 dB
- Analogue inputs: 3 (RCA pairs), Phono (MM) input
- Digital inputs: USB-C, Coaxial (RCA), Optical (Toslink), HDMI ARC
- Bluetooth 5.4 with adaptive aptX™ technology and AAC
- Only DSD supported on USB-C: 1024, 512, 256, 128, 64
- Headphone output – Maximum output level (RMS) into 32 ohms/300 ohms: 2.5V/5V – Load
- range: 16 ohms – 2 kOhms
- Mains voltage: 100V or 110-120V or 220-240V, 50-60Hz
- Power consumption (maximum): 500W
- Power consumption (standby): <0.5W
- Dimensions W x D (including speaker terminals) x H (including feet): 431 x 344 x 83mm
- Weight (net): 9kg