Lehmann Audio Linear D MKII silver

Since 2004, Lehmann Audio’s Linear range has given headphones a second life by freeing them from the mediocre outputs of conventional amplifiers. The Linear D added an integrated digital-to-analog converter. This MKII version uses the same compact chassis, but features a completely redesigned analog board and more selectively chosen components. Made in Cologne, it combines three functions: headphone amplifier, converter, and preamplifier.

Three devices in a 28 cm enclosure

The Linear D MKII is a hybrid device. It amplifies the headphone signal with a discrete Class A output stage. It converts digital streams via an ESS Sabre K2M chip. And it can serve as a preamplifier to drive active speakers or a power amplifier, thanks to its RCA line output.

This versatility makes it a natural companion for CD players, network players, and turntables (via an upstream phono preamp). Connected digitally to a network player, it allows listening through headphones and speakers without multiplying boxes. When the gain is set to 0 dB and no headphones are connected, it works as a full-fledged preamplifier.

An analog board thoroughly reworked

The most significant change compared with the first version of the Linear D lies in the analog board. Lehmann Audio has adopted the so-called “Low-Z Copper” technology: a low-impedance manufacturing process that increases the cost of the bare printed circuit boards by about ten times, according to the manufacturer. The copper traces are six times thicker than on the previous model, which reduces the electrical resistance of the signal path.

The capacitors in the audio path are Mundorf MLytic units, whereas the first version used standard-grade components. The internal wiring is now OFC (oxygen-free copper). These component choices come in part from the Linear SE, the range’s purely analog high-end model. The measured result: better dynamic figures, and more faithful transient reproduction.

Digital conversion and source management

The digital section is based on an ESS Sabre K2M chip mounted on a four-layer printed circuit board protected against high-frequency interference. Mica capacitors (low-loss) filter the analog signal at the converter output, and fast amplification stages on the converter board preserve transient quality.

Two digital inputs are available: one optical (Toslink) and one coaxial (S/PDIF). The device handles streams up to 24 bits / 192 kHz. Source selection is automatic: if a digital signal is detected, it takes priority (the optical input taking priority over the coaxial one). In the absence of a digital signal, the Linear D MKII switches to the RCA analog input. There is no input selector on the front panel, which contributes to the device’s minimalism, but also means that the switching logic cannot be controlled manually.

Headphone outputs and gain adjustment

Two 6.35 mm jack sockets equipped with Neutrik connectors with gold-plated contacts are located on the front panel. Both outputs operate in parallel and can simultaneously power two headphones of the same impedance, without noticeable signal degradation. The left output automatically cuts the rear RCA line output when headphones are plugged into it: a useful feature for switching silently between headphone listening and speaker listening.

With 400 mW at 60 Ω and 200 mW at 300 Ω, the Class A output stage is sized to power high-impedance headphones as well as current-hungry planar magnetic models. The output impedance is 5 Ω, low enough not to alter the frequency response curve of most dynamic headphones.

Four gain levels are available (0 dB, 10 dB, 18 dB, 20 dB), adjustable via micro-switches located under the chassis. This placement avoids any accidental operation, but requires turning the device over to change the setting. Lehmann Audio had the good idea of printing the setup instructions directly under the enclosure.

Mechanical isolation and construction

The aluminum chassis measures 11 × 28 × 5 cm and weighs about 1.5 kg. Its front panel is understated: a single large, damped volume knob, and the two headphone outputs. Nothing else. Three finishes are offered: black, silver, and chrome.

Under the enclosure, three 3S absorber feet (formerly SSC) provide mechanical decoupling. These feet use a string suspension system (String Suspension Concept) developed by Manfred Diestertich, chief engineer at Audio Physic. The principle: micro-vibrations picked up by the chassis are converted into heat by a three-part suspension element incorporating a technical textile. The same type of technology equips Audio Physic speakers. On a headphone amplifier, the benefit mainly concerns the reduction of parasitic mechanical noise transmitted by the furniture.

What changes compared with the Linear D (first generation)

For owners of the original Linear D, the MKII is not just a simple cosmetic refresh. The analog board is fundamentally different: Low-Z copper, Mundorf MLytic capacitors, OFC wiring. The 3S absorber feet replace the standard feet. Lehmann Audio also offers an upgrade from the old to the new board for owners of previous models, all Linear generations combined, with installation of the 3S feet as an option.

Total harmonic distortion remains below 0.001% (at 6 mW / 300 Ω), the signal-to-noise ratio exceeds 100 dB at zero gain, and the frequency response extends from 10 Hz to 35 kHz. The measured specifications are comparable, but the gains lie in the realm of micro-dynamics and spatial reproduction, parameters that raw figures capture only imperfectly.

Technical Specifications

Architecture

• Class A design
• Double-sided printed circuit boards with optimized routing, high-purity copper
• Mundorf MLytic audiophile capacitors
• High-performance OFC copper internal wiring

Performance

• Output power
  • 400 mW at 60 Ω
  • 200 mW at 300 Ω
• Frequency response: 10 Hz (± 0.3 dB) to 35 kHz (± 1 dB)
• Signal-to-noise ratio: greater than 100 dB (0 dB gain)
• Total harmonic distortion (THD): less than 0.001% (6 mW / 300 Ω)
• Output impedance: 5 Ω

Settings

• Adjustable gain: 0 dB, 10 dB, 18 dB, 20 dB (switches located on the underside of the chassis)

Digital Conversion

• Latest-generation ESS Sabre converter
• Maximum resolution: up to 24-bit / 192 kHz
• Precise and natural reproduction, close to an analog signature
• Source management: automatic detection with priority given to analog input

Connectivity

• Inputs
  • 1 stereo analog input (RCA)
  • 1 coaxial digital input (SPDIF)
  • 1 optical digital input (Toslink)
• Outputs
  • 2 x 6.35 mm jack outputs (Neutrik connectors, gold-plated contacts)
  • 1 pre-out output (RCA) for active speakers or power amplifier

Mechanical Isolation

• Integrated SSC (String Suspension Concept) feet for effective vibration reduction

General Specifications

• Dimensions: 11 x 28 x 5 cm
• Weight: approximately 1.5 kg
• Power consumption: approximately 15 W
• Available finishes: black, silver, chrome

Improvements Over the Previous Version

• Printed circuit board: double-sided high-purity copper (vs. standard on the V1)
• Capacitors: Mundorf MLytic (vs. standard audiophile on the V1)
• Internal wiring: high-performance OFC copper (vs. standard on the V1)
• Isolation: SSC feet included (vs. standard feet on the V1)
• Sound reproduction: more detailed, with improved micro-dynamics