The way we listen constantly moves andevolves. With more of us interested in quality headphone listening than everbefore, we decided to make a headphone amplifier with a wider reach. The brieffor the 931 project was to keep all of the essential elements that once madethe highly acclaimed 933 so successful but at a significantly lower cost. The931i (improved) may be affordable, but its performance and quality is stillpure Trilogy.

The 931i is a fully discrete design, nogeneric integrated circuits are used, so designer Nic Poulson can control allthe active circuit's crucial parameters, optimising performance for itsintended application only. The small, light drivers found in headphones arevery closely coupled to the ear and as a result are ruthlessly revealing.

Like its illustrious kin the 933, the audiocircuit operates in pure single ended Class A with active constant currentsources. Each channel has a single continuously biased output device. The mainbenefits of this topology are that the output is free from crossoverdistortion, and the device is held at a constant temperature. An oversizedlinear power supply gives good operating headroom for the active circuitry. Allthese elements combine to give excellent small signal resolution whilemaintaining good drive capability.

There are two stereo line inputs, audiograde ALPS volume control and quality components from branded sources usedthroughout. Assembly is totally by hand in our UK workshops. The output devicesdissipate enough heat to need heatsinking. An extruded off the shelf heatsinkwould serve here but we chose to employ a custom CNC machined part.Semiconductors are sensitive to mechanical vibration and their operatingcharacteristics vary with temperature. The sound quality benefits of attachingthe output devices to a high mass with low resonant signature and large thermalinertia more than offset the increased costs.

The standard finish is a soft naturalsilver, enhancing the quality of the beautifully finished casework. Ourlustrous paint finishes are a luxurious option for those wishing to add theirown individual touch.

Intelligent design can overcome theconstraints of finite resources. The 931i carries all the traits that make itsbigger brethren such involving musical performers. Detailed, spacious,communicative, the 931i is indisputably Trilogy through and through.