The A1.5 delivers power and drive in stereo, mono, bi-amped or bridged modes, with supreme composure and clarity. With its highly customisable global feedback and gain settings, the A1.5 gives its owner the power to integrate the speaker of their choice into almost any listening room. Coupled with the flexibility in its basic configuration, allowing stereo, mono, bi-amp or bridged setup, the A1.5 stands out from its competition as a unique, highly innovative product in its class.
A1.5 Two-channel Power Amplifier
Like its bigger brother, the M1.1 Reference power amplifier, there’s a lot more to the A1.5 than meets the eye – just in a more compact and more affordable form…
Faced with exactly the same challenges as the M1.1, the A1.5 embodies the same sophisticated, modular and scalable approach. It might be (slightly) smaller than the M1.1 and around two-thirds of its weight, but it’s still four amplifiers in one. It still offers the same adaptable, software controlled topology, adjustable input configuration and gain, user selectable global feedback ratio and cost-effective upgrade path. It offers exactly the same, incredibly short signal path, fully discrete, fully balanced and fully complementary circuit, built with the same carefully selected components to the same exacting standards. Even the casework, although shorter, has the same footprint, uses the same construction and includes the same mechanical grounding/stacking system. In fact, in every important way, the A1.5 is, quite literally, an M1.1 writ small – or, in Hollywood terms, “Honey, I shrank the amp…”
But in this case, loss of weight doesn’t mean a loss of quality. The power transformer and reservoir capacitance are identical in type and design to those in the M1.1. The A1.5 inevitably delivers less power than the M1.1 Reference amplifier but with a conservatively rated output of 150 watts/channel, it’s definitely no lightweight, performing with real dynamic range and authority – and it does it all at a considerable saving in cost. It might not match the awesome headroom capabilities of the M1.1 under the most demanding loads, or do it in the largest of large rooms, but in many systems and with many speakers you simply don’t need or can’t use that capacity. Combine the A1.5’s impressive real-world performance and increased affordability with its adaptable, configurable topology and suddenly you have a serious slice of M1.1 performance – but in a much more manageable package.
With the same transparency, resolution and engaging, communicative musical qualities as the M1.1, the A1.5 is an incredibly capable and convincing performer, the perfect partner for a whole host of high-quality speakers. In any other range it would be the flagship model and it delivers performance to match. But what happens when the upgrade urge strikes, you can accommodate bigger speakers or you want more from your system? As impressive as a single A1.5 undoubtedly is, adding a second A1.5 to your system unleashes the monster within, because, just like the M1.1, the configurable input/output topology of the A1.5 makes it an amplifier that, once doubled up, becomes considerably more than the sum of its parts. User configurable, via the front-panel buttons or the CH-Control App, the A1.5 is not only a conventional stereo amplifier: it is a high-current mono-bloc: it is a high- power bridged mono-bloc and perhaps most important of all, it can be adapted for bi-amping, a single input being routed to both channels. That not only saves on the need for additional interconnects, the gain and global feedback ratio can be set independently for each channel, allowing further control over bass output and room matching. But most critically of all, vertical bi-amping maximises dynamic range and system headroom, allowing the A1.5 to grow with your speakers’ demands and your musical and system ambitions.
The A1.5 – the not so ‘little’ power amp that punches well above its weight!
The A1.5 power amplifier has been developed with modularity in mind. It can be equipped with a single analogue input board in case the A1.5 is used as a single channel but a second analogue input board can also be fitted from factory for stereo operation. This modularity ensures the following operation modes:
- stereo mode
- single channel (mono) mode
- bi-amplification modes, both passive and active
- bridge mode
Changing the A1.5 operating mode is easy and can be done on-the-fly from the front panel user interface and our tablet app. Only the available options are visible depending of the hardware configuration.
The central power supply is taking most of the internal space of the chassis. The huge 1’700VA transformer is mounted on silent-blocks to avoid at maximum its vibrations to be fed-back into the sensitive part of the circuitry. It is shielded both with a magnetic screen and an electrostatic one. The transformer plate is also secured for transportation.
For optimum thermal performances, the output stage diode bridges are mounted directly onto the amplifiers heatsinks and are of hyper-fast soft-recovery type.
The A1.5 features extremely low-ESR filtering capacitors ensuring tremendous current capabilities for controlling the most demanding speakers.
All analogue stages inside the A1.5 are built only with discrete components, no operational amplifier have been used into these sections. This deliberate choice warranties the shortest audio signal path and allows the use of custom-made building blocks.
No capacitors have been used in the signal path, nor any output relay to ensure maximum transparency.
A gain range of 24dB – with steps of 0.5dB – is embedded into each channel, for a perfect match with the loudspeakers sensitivity and room size. A lower gain is typically preferred for high-sensitivity speakers into a small room while a bigger gain is sometimes needed for large rooms with sensitivity loudspeakers.
This gain adjustment can also be useful with multi-amplified loudspeakers to fine-tune the various drivers level.
Output Stage Feedback
The A1.5 output stage features the renown CH loudspeaker matching circuitry. The ratio between the global and local feedbacks is adjustable on-the-fly from the front panel user interface or through our tablet app. Like the A1, the A1.5 has 6 feedback ratio positions. But finer tuning is available at low global feedback, so global/local feedback ratios of 0/100, 10/90, 20/80, 40/60, 70/30 and 100/0 are available.
A different feedback ratio can be set for each channel in bi-amplification mode allowing an even finer tuning of the connected loudspeaker.
Keeping the output stage bias current constant ensures the amplifier to remain as linear as possible. The bias current is highly sensitive to temperature changes.
ExactBias has been designed to maintain the output stage bias current constant, by monitoring both the amplifier heatsink and output transistors temperatures, irrespectively of the musical program and room temperature.
In terms of performance, the A1.5 class-AB designed with ExactBias technology outperforms a pure class-A design with usual bias compensation.
The voltage and current delivered to the loudspeakers is permanently monitored thanks to a non-intrusive circuitry. A digital signal processor not only works out in real-time the effective output power, but also protects the amplifier in case of a short-circuit across the loudspeaker binding posts.
“Importantly, the improvements result in a more musically engaging delivery. The A1.5 is nothing short of a giant killer amp. Yup: miracles do exist! Even at 3 minutes into the listening session, I already knew that there was no way back!” – CHRISTIAN PUNTER, HIFI-ADVICE.COM (read in full here)
|Inputs type||Balanced (XLR), one connector per board
Single-Ended (RCA & BNC), one connector per board
|Input impedance||Balanced: 94kΩ
Single-Ended: 47kΩ or 300Ω
|Input stage||JFET input stage
Ultra-low noise, discrete fully differential stage
24dB range adjustable gain in 0.5dB steps
|Amplification stage||Ultra-low noise full discrete class AB design
5 pairs of complementary output transistors
|Output Power||2x 150W / 8Ω, 2x 275W / 4Ω, 2x 450W / 2Ω in stereo and bi-amp modes
1x 275W / 4Ω, 1x 450W / 2Ω, 1x 700W / 1Ω in monaural mode
1x 550W / 8Ω, 1x 800W / 4Ω, 1x 1200W / 2Ω in bridge mode
|Bias||Patent-pending bias circuitry for constant bias operation|
|Feedback||Unique user programmable local/global feedback ratio of the amplification stage|
|Bandwidth||DC to 450kHz (-3dB) at 1W into an 8Ω resistive load|
|Signal to Noise Ratio||Better than 115dB in stereo and bi-amp modes
Better than 118dB in bridge mode
|Total Harmonic Distortion + Noise||Less than 0.1% with 0% global feedback
Less than 0.01% with 100% global feedback
|Binding posts||Two pairs of Argento binding posts for loudspeakers connection|
|Monitoring||Non-intrusive DSP-based protection of the amplifier
Instantaneous voltage & current values are permanently monitored for each channel
Disconnected loudspeaker detected
Over-temperature of the heatsink
Over-temperature of the output transistors
|Transformer||1’700VA single transformer, oversized for low-noise operation|
|Power capacitors||2x 82’000uF/63V capacitors with ultra-low ESR/ESL|
|Regulators||Non-regulated symmetrical power supply for the power stages
Eight local regulation stages for input/driver stages
Seven local regulation stages for the logic/display
|Display||480×272 pixels, 24bits colour, AMOLED|
|Mains operation||Selectable 100V, 115, 230V AC, 47-63Hz|
|Fuses value||Standby fuse (diameter 5mm): 250mA T (230V AC), 500mA T (100V AC, 115V AC)
Power fuse (diameter 6.3mm): 10A T (230V AC), 20A T (100V AC, 115V AC)
|Power supply consumption||<1W (standby), 1200W max in operation|
|Dimensions (L x D x H)||440mm x 440mm x 186mm (main body)
440mm x 492mm x 198mm (overall including connectors and feet)
|Remote control||Ethernet based system control via the Android CH Control App|