Grace Design M903
Reference Headphone Amplifier, DAC, monitor control

The m903 from Grace Design - the most refined and feature rich headphone amp, DAC and compact monitor controller available.

The m903 keeps everything great about its predecessors, adds some useful new features, and ups the ante with even more audio performance. A new volume control provides higher headroom and lower distortion and noise. New generation DAC's and ultra-low noise balanced current to voltage converter yields even more musical performance compared to the m902. Improved s-lock PLL circuitry delivers even lower phase noise and jitter. An improved power supply isolates headphone amplifiers, line amplifiers, DAC's and digital logic, resulting in lower noise and distortion.

Perhaps the most exciting improvement is the all new high speed USB interface. This cutting edge technology provides a completely asynchronous data transfer mode which allows for bit-perfect USB playback with zero interface induced jitter. This new interface affords standard driverless USB Class 1 operation on Windows and Mac up to 24bit/96kHz and USB Class 2 audio for 24bit/192kHz operation on Windows and Mac (drivers needed for 192kHz operation under Windows). This is computer-based audiophile playback, perfected.

New crossfeed circuitry is even more useful and includes a gentle compensation to eliminate the perceived loss of low frequency content. Both balanced and unbalanced line outputs are now standard, with individual volume controls for each. Grace Design even included a mono mode for checking a mix for phase issues or simply monitoring in mono. These improvements cement the m903 as the perfect compact, audiophile grade monitor controller, even for larger scale production environments with more than one set on monitors.

A full complement of analog and digital inputs are provided (balanced, unbalanced, AES3, S/PDIF, TOSLINK and USB), which are selectable via a precision rotary front panel switch. And Grace Design offers an updated optional infrared remote control, which provides essential control for anyone working out of reach of their m903. The m903 - setting the standard for compact, precision playback tools.

Features:

• Balanced and unbalanced analog inputs
• 24bit/192kHz digital stereo inputs- AES3, S/PDIF, TOSLINK and USB
• High speed USB interface - completely asynchronous transfer mode allows for bit-perfect playback with zero interface induced jitter
• Driverless operation on Windows & Mac up to 96kHz/24bit
• Supports USB Class 2 audio specification for 192kHz/24bit operation on Windows & Mac (drivers needed for 192kHz operation under Windows)
• New generation DAC’s and ultra low noise balanced current to voltage converter yields more musical performance compared to the m902
• Mono mode for checking mix phase issues (or listening to Pet Sounds)
• s-Lock™ phase lock loop sample clock regeneration for ultra-low jitter and rock solid digital stability
• High-current transimpedance headphone amplifier circuitry built to effortlessly drive low impedance headphones
• Balanced and unbalanced variable level analog line outputs
• Improved power supply architecture isolates headphone power amplifiers, line amplifiers, DAC’s and digital logic
• Precision level control with a 99.5dB range in 0.5 dB steps
• Channel level matching accuracy of 0.05dB
• Improved x-feed circuit eliminates perceived loss of low frequency content
• Optional infrared remote control available
• Internal linear power supply with custom wound toroidal transformer
• Sealed gold contact relays used for all signal switching
• Five year transferable warranty on parts and labor

Specifications:
ANALOG IN

• Gain:
    -  Headphone output, volume at max, trim at +9.5: +15dB
    -  Balanced Line output, volume at max, trim at +9.5: +14dB
    -  Unbalanced Line output, volume at max, trim at +9.5: +11dB
• Frequency Response:
    -  @ 0dBu out +/- .25dB: 22Hz – 120kHz
    -  @ 0dBu out +/- .5dB: 12Hz – 260kHz
    -  @ 0dBu out +/-3dB: 4Hz – 600kHz
• Maximum Input Level:
    -  Balanced Input: +22dBu
    -  Unbalanced Input: +22dBu
• Maximum Output Level:
    -  Unbalanced output @1kHz, 100k Ohm load: +22.5dBu
    -  Balanced output @1kHz, 100k Ohm load: +27dBu
    -  Headphone output @1kHz, 50 Ohm load: +20.4dBu
• Impedance:
    -  Balanced Input: 106K Ohms
    -  Unbalanced Input: 53K Ohms
    -  Balanced Output: 95 Ohms
    -  Unbalanced Output: 47.5 Ohms
    -  Headphone Output: 1.2 Ohm
• THD+N:
    -  Headphone +10dBu out, 50 Ohm load, SMPTE 4:1 <0.01%
    -  Headphone +10dBu out, 50 Ohm load <0.008%
    -  Unbalanced Line Out +10dBu out TBD
    -  Balanced Line Out +10dBu out <0.002%
• Attenuator:
    -  Channel matching <0.05dB
    -  Attenuator Range 99.5dB

D/A CONVERTER

• Input Sample Rate: 32, 44.1, 48, 88.2, 96, 176.4, 192kHz
• THD+N:
    -  44.1kHz, 24bit, 1kHz, +20dBu out <0.002%
• Noise Floor:
    -  0dB gain, 22-22kHz -94dBu
    -  0dB gain, A-weighted -97dBu
• Power Requirements:
    -  120VAC .16A
    -  230VAC .08A
• Dimensions and Weight:
    -  Dimensions H1.7” x W8.5” x D8.25”
    -  Weight 5 lbs (2.2kg)