Trilogy 931 Headphone Amplifier
The way we listen constantly moves and evolves. With more of us interested in quality headphone listening than ever before, we decided to make a headphone amplifier with a wider reach. The brief for the 931 project was to keep all of the essential elements that once made the highly acclaimed 933 so successful but at a significantly lower cost. The 931i (improved) may be affordable, but its performance and quality is still pure Trilogy.
The 931i is a fully discrete design, no generic integrated circuits are used, so designer Nic Poulson can control all the active circuit’s crucial parameters, optimising performance for its intended application only. The small, light drivers found in headphones are very closely coupled to the ear and as a result are ruthlessly revealing.
Like its illustrious kin the 933, the audio circuit operates in pure single ended Class A with active constant current sources. Each channel has a single continuously biased output device. The main benefits of this topology are that the output is free from crossover distortion, and the device is held at a constant temperature. An oversized linear power supply gives good operating headroom for the active circuitry. All these elements combine to give excellent small signal resolution while maintaining good drive capability.
There are two stereo line inputs, audio grade ALPS volume control and quality components from branded sources used throughout. Assembly is totally by hand in our UK workshops. The output devices dissipate enough heat to need heatsinking. An extruded off the shelf heatsink would serve here but we chose to employ a custom CNC machined part. Semiconductors are sensitive to mechanical vibration and their operating characteristics vary with temperature. The sound quality benefits of attaching the output devices to a high mass with low resonant signature and large thermal inertia more than offset the increased costs.
The standard finish is a soft natural silver, enhancing the quality of the beautifully finished casework. Our lustrous paint finishes are a luxurious option for those wishing to add their own individual touch.
Intelligent design can overcome the constraints of finite resources. The 931i carries all the traits that make its bigger brethren such involving musical performers. Detailed, spacious, communicative, the 931i is indisputably Trilogy through and through.
