Grace Design M903

Reference Headphone Amplifier, DA Converter and Preamplifier The m903 is a stereo headphone amplifier, D/A converter incl. USB interface and preamplifier in a 1U case with half 19" rack width. The m903 provides professional and excellent sounding headphone and stereo monitoring for music, post production and mastering, whether from analog or digital stereo sources, as well as directly from Mac/PC. It can also serve as an excellent reference D/A converter and system preamp, as well as an excellent headphone amplifier for audiophiles.

Specifications

General

• Manufacturer: Grace Design
• Model: m903
• Year built: 2011 onwards (predecessor model m902).
• Made in: USA
• Color: Stainless steel (natural and black)
• Weight: 2,2 kg
• New price approx.: € 1900,-.

Connections The m903 offers balanced as well as unbalanced analog inputs in stereo via XLR and RCA jacks, for +4dBu as well as -10dBV analog sources. The front panel 6.3mm stereo jacks are wired in parallel and can be used with two headphones simultaneously. In addition, the m903 has two stereo line outputs (balanced & unbalanced) on the rear panel that allow the m903 to be used as a high-end monitor controller. These two line-out pairs are separately adjustable in level. Grace Design's signature high-current, transimpedance output amplifiers are optimized to perfectly drive even the lowest impedance headphones. The precise volume controller controls both headphone outputs as well as line out levels in exact 0.5dB steps within a 95dB range.

Digital sources are connected at the rear as AES3, S/PDIF or optical inputs via XLR, Cinch and Toslink. An ingenious additional feature is the USB input which provides a high quality direct connection to the computer as a digital input source. A front panel rotary switch selects between analog, digital and USB sources, a 4-LED display shows the detected sample rate of digital sources between 44.1 and 192kHz. An up-to-date, high quality 24bit DAC, with Grace Design's own s-Lock(™) dual stage PLL (Phase Lock Loop) performs the D/A conversion with amazing sonic results and extremely low jitter.

Special Features The m903 also incorporates the crossfeed circuit, or x-feed, known from its predecessor, which simulates the natural acoustic environment of loudspeaker listening and the effect of HRTF (Head Related Transfer Functions). This circuit, designed by Dr. Jan Meier, improves stereo imaging and reduces fatigue when listening through headphones.

Compared to its predecessor, the m902, some significant sonic improvements have been realized in the m903, these include:

• A new USB interface with asynchronous transfer mode for bit-transparent playback without additional jitter through the interface - driverless operation on Mac up to 24bit/192kHz (Windows computers require drivers for 192kHz operation).

• Latest generation D/A converter with reworked analog signal path achieves even more musical performance, with 10dB improved dynamic range.

• A newly developed volume controller with greater headroom, improved signal-to-noise ratio and even lower distortion levels.

• Improved headphone output protection circuitry and gold-contact relays for silent on/off switching.

• Balanced and unbalanced analog line outputs with individual level control.

• Improved s-Lock PLL circuitry with lower phase noise and jitter.

• Improved X-feed circuitry that eliminates the perception of lower low frequency content.

• Improved power supply architecture isolates headphone amplifier, line amplifier, DAC and digital logic circuitry.

Reviews

On the Audio Import product page (see link below) you will find the test reports from STEREO (April 2011) as well as HiFi DIGITAL (March 2011) for download.

Links

• [[1]] Audio Import product page

• [[2]] Grace Design manufacturer page