Reference headphone amplifier, DAC, monitor controller



As of September 2014, the m903 has been discontinued. Its replacement, the m920, can be found here.

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.

Optional m903 Infrared Remote Control

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.



  • features
  • specs
  • computer setup help
  • video
  • 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




Headphone output, volume at max, trim at +9.5
Balanced Line output, volume at max, trim at +9.5
Unbalanced Line output, volume at max, trim at +9.5
Frequency Response
@ 0dBu out +/- .25dB
22Hz 120kHz
@ 0dBu out +/- .5dB
12Hz 260kHz
@ 0dBu out +/-3dB
4Hz 600kHz
Maximum Input Level
Balanced Input
Unbalanced Input
Maximum Output Level
Unbalanced output @1kHz, 100k Ohm
Balanced output @1kHz, 100k Ohm
Headphone output @1kHz, 50 Ohm load
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
@ -10dB gain
Headphone +10dBu out, 50 Ohm load, SMPTE 4:1
Headphone +10dBu out, 50 Ohm load
Unbalanced Line Out +10dBu out
Balanced Line Out +10dBu out
Channel matching
Attenuator Range
Input Sample Rate
32, 44.1, 48, 88.2, 96, 176.4, 192kHz
44.1kHz, 24bit, 1kHz, +20dBu out
Noise Floor
0dB gain, 22-22kHz
0dB gain, A-weighted
Output level
Unbalanced Output @ 0dBFS
Balanced Output @ 0dBFS
Power Requirements
Dimensions and Weight
H1.7 x W8.5 x D8.25
5 lbs (2.2kg)

Regardless of the type of computer you will use to playback audio from, it must have at least one available USB port. The m903 ships with a standard USB type A to type B mini cable. The type A connector plugs in to the computer and the type B mini connector to the USB m903 input.

The m903's asynchronous mode USB DAC supports standard driverless operation on MAC to 192kHz and on PC to 96kHz. For sampling rates above 96kHz, PC users will need to download and install a free driver on their computer. This driver can be found here Windows USB 2 Driver v1.26. Driverless operation basically means 'plug and play'. The m903 will automatically show up in your computer's list of supported audio devices as 'Grace Audio Device'. In most cases, simply choose that as your audio playback device and the system will work.

Different operating systems and audio players will pose their own set of complications in setting up the m903 as the audio playback device. In the event that 'plug and play' operation does not occur, you will need to look at some specific setup variables for your player and OS. In this case, we will direct you to a very well written and comprehensive document by our friend and colleague Charles Hanson from Ayre Acoustics.

This is an invaluable resource for computer/USB audio setup information for most current operating systems, and we strongly urge you to familiarize yourself with the information pertaining to your specific OS.

Another resource is Wavelength Audio's website:
In the event that you have any setup issues which aren't addressed by these resources, feel from to contact us directly at 303.443.7454 Monday through Friday 9 – 5, MST.