Lehmann Audio LINEAR USB II

The Linear USB II is a headphone amplifier with an integrated digital-to-analogue converter, designed to transform headphone listening from digital sources such as a computer, a Mac or a mobile phone. It also serves as a preamplifier, with a pre-out output capable of powering active speakers.

The unit features an analogue board using Low-Z Copper technology and an ESS Sabre K2M chipset, with an analogue filter using Silver Mica capacitors. The converter accepts streams up to 384 kHz at 32 bits, in PCM, DOP 128, FLAC, MP3 and WAV formats, with a maximum DAC output level of 1.8 V RMS. The USB-B input automatically detects the incoming audio stream, with no need for a manual input selector.

Gain can be set to four positions (0 dB, 10 dB, 18 dB or 20 dB) via DIP switches, allowing the amplifier to be matched to headphones with very different sensitivities. Output power reaches 400 mW at 60 ohms and 200 mW at 300 ohms, with an input impedance of 47 kOhms and an output impedance of 5 ohms for the headphone output and 50 ohms for the pre-out output. The signal-to-noise ratio exceeds 100 dB at 0 dB gain, harmonic distortion remains below 0.001% at 6 mW at 300 ohms, and channel separation exceeds 80 dB at 10 kHz. Frequency response spans from 10 Hz to 35 kHz.

Two headphone outputs allow simultaneous listening for two people, each connected via Neutrik connectors with gold-plated contacts. Gold-plated RCA outputs, with Teflon insulation, complete the connectivity. 3S damping feet decouple the unit from its support to limit vibrations.

This type of amplifier is aimed at a music lover equipped with demanding hi-fi headphones, who wants to make use of digital sources (PC, Mac, mobile) without going through the limited headphone output of a computer or a conventional hi-fi amplifier. The ability to connect two headphones and drive active speakers via the pre-out output also makes it a central hub for a desk or a small listening system.