M903 Reference headphone amplifier, DAC, monitor controller
Ten years ago, we launched the model 901 headphone amplifier. 4 years later, the m902, which set the standard for a new category of compact, precision playback tools. Today, we proudly unveil the m903, which is simply 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 breathtaking 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. We have 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 we offer an updated optional infrared remote control, which provides essential control for anyone working out of reach of their m903.

Advancing the tradition of unmatched audio performance and functionality, the m903 is now the ultimate solution for high resolution audio playback. From the very top mastering engineers to the most discerning audiophiles – it is a must for anyone searching to discover new depths in music and sound.

applications
>    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 play  back 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

specs
PRELIMINARY 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     +22.5dBu
Balanced output @1kHz, 100k Ohm     +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

Dynamic Range     

@ 0dB gain     TBD
@ -10dB gain     TBD

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     TBA
Balanced Line Out +10dBu out     <0.002%

Attenuator     

Channel matching     <0.05dB
Attenuator Range     99.5dB

SPECIFICATIONS 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

Output level     

Unbalanced Output @ 0dBFS     TBD
Blanced Output @ 0dBFS     TBD

Power Requirements     

120VAC     .16A
230VAC     .08A

Dimensions and Weight     

Dimensions     H1.7 x W8.5 x D8.25
Weight     5 lbs (2.2kg)