Wizard High-End Audio Blog: August 2018

A1.5 will be released in November 2018.

Meet the A1 successor. Featuring a huge new power supply design, the A1.5 power amplifier effortlessly delivers up to 150W / 8 Ohms per channel in Stereo mode or 1200W / 2 ohms in Bridge mode. The A1's flexibility of use and future-proof modularity have been kept untouched allowing the amplifier to be reconfigured from Stereo to Bi-amplification, Monaural or to Bridge at the push of a button. CH Precision’s unique ExactBias circuitry as well as the critically acclaimed loudspeaker matching topology forge the heart of the A1.5.

Further refined, taller, more powerful, the A1.5 is in every way an A1... and a half!

What’s more, every A1 ever produced can be upgraded to an A1.5 amplifier.

Features:

Modularity
The A1.5 power amplifier has been developed with modularity in mind. It can be equipped with a single analog input board in case the A1.5 is used as a single channel but a second analog input board can also be fitted from factory for stereo operation. This modularity ensures the following operation modes:

Stereo mode
Single channel 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.

Power Supply
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 tremendeous current capabilities for controlling the most demanding speakers.

Analog stages
All analog 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.

Gain
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 low-sensitvity loudspeakers.

This gain adjustment can also be useful with multi-amplified loudspeakers to fine-tune the various drivers level.

Output stage feedback
Like with the A1, the A1.5 output stage features the 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. Each step is 20%, going from 0% - local feedback only - to 100%.

A different feedback ratio can be set for each channel in bi-amplification mode allowing an even finer tuning of the connected loudspeaker.

ExactBias
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.

Protections
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.