Sapphire FBA-800

The Sugden Sapphire FBA-800 is a Pure Class A stereo power amplifier, designed and manufactured by Sugden at its premises in West Yorkshire, England. Its development focused on musical performance, a practical user interface, pride of possession and product longevity, while also taking account of current technology trends.

The FBA-800 is a floating bridge power amplifier operating in Pure Class A output mode, with an output of 40 watts per channel and a 350VA toroidal transformer. It has balanced and phono/RCA asymmetric inputs, each provided as a stereo pair, with output through a stereo pair of speaker binding posts. The amplifier can operate in full balanced mode from input to output, using 2 amplifiers per channel in balanced configuration.

Input sensitivity can be reduced by 6dB in 1 step, allowing adjustment of the balance and matching between the audio chain, preamplifier, power amplifier and loudspeakers. This setting is selected using a push button on the front panel. A second front-panel push button selects between the balanced and phono/RCA inputs.

Each channel contains 2 amplifiers working as voltage amplifiers, driving an output stage of bridged power transistors. With the output earth floating, the bridged configuration provides a low noise floor, increased power output relative to the voltage rails by a factor of 2, low output impedance through the fixed current of Class A operation, and improved load tolerance. The amplifier has been designed for modern high-efficiency loudspeakers.

The power amplifier is DC coupled and uses a servo lock to maintain low-frequency detail. A DC protection circuit is included for safety. It uses extremely low-impedance MOSFET switching devices and statically switches the protection circuit, which also soft-switches the power amplifier on and off.

The low-impedance power supply uses 1 custom-made bifilar-wound transformer with 4 separate windings. The main smoothing capacitors for the output stage were developed for professional audio applications and provide suitable ripple characteristics and long life. Each channel has 4 multi-emitter power transistors in its output stage, with an output capability of 26 amps per device.

Sugden has extensive experience in Class A amplification and uses through-hole components instead of surface-mount components where possible, supporting product life, performance and reliability. The FBA-800 has gold-plated circuit boards and high-quality internal silver wiring, alongside its carefully developed electronic circuitry, components and casework.

The amplifier underwent thousands of hours of tuning and development before reaching production, with the completed FBA-800 intended as a link to Simply More Music.