Grace Design m906 Reference Monitor Controller

  • $ 6,265.00
  • Save $ 330

At the core, the m906 is a purist level control for monitoring surround (or stereo) audio sources. But a closer look reveals a highly intelligent feature set that makes it a vital nerve center for any recording, mastering, or post facility centered around a digital audio workstation. It is configured as a 2U rack mount mainframe controlled by a sleek, powerful desktop remote control, with all audio kept in the mainframe and all control via the remote control.

The m906 offers a full complement of balanced and unbalanced analog 5.1 and digital 5.1 and stereo inputs, the latter featuring our latest generation reference 24bit/192kHz DAC technology with our proprietary s-Lock™ PLL for rock solid digital stability. All inputs and outputs on the m906 can be user calibrated for seamless integration into any playback environment with all types of playback equipment.

The m906’s signal path is designed to deliver nothing short of the best performing, transparent audio available. All components are chosen for audiophile performance and long term reliability. Level controls, the heart of a monitor controller, are low distortion precision devices which provide a 100dB range in silent .5dB steps.

Included as a standard feature is our acclaimed reference headphone amplifier circuitry (from our m902), with one output jack on the mainframe and one additional output on the remote. This unique circuitry provides precision headphone amplification for critical monitoring, mixing and mastering.

This m906 can be equipped with an optional DOWNMIX module that creates a stereo L+R mix of a 6 channel surround source. All standard Dolby mix ratios can be calibrated by the user for both the center and surround channels.

While the m906 boasts a remarkably full set of features, the real achievement for us is to offer this while maintaining the impeccable, transparent audio performance for which all of our products are famous.


  • multiple 5.1 and stereo analog inputs
  • 24bit/192kHz digital 5.1 and stereo inputs- AES3, S/PDIF, ADAT and TOSLINK
  • s-Lock™ phase lock loop sample clock regeneration for ultra-low jitter and rock solid digital stability
  • precision speaker and headphone level controls with a 100dB range in 0.5dB steps
  • every electrical and mechanical design element maximized for absolute purist audiophile performance
  • all controls are built into an elegant, convenient desktop remote control unit
  • all I/O and audio are routed in a 2U rack mount mainframe powered by an external 1U 1/2 rack power supply
  • control up to three speaker systems - two 5.1 or up to three stereo
  • m902 style high-current audiophile headphone amplifier built in with one output on remote control unit and one on the mainframe unit
  • complete system level calibration (inputs, outputs, inter-channel balance, dim) and individual channel solo/mute
  • balanced talkback microphone input and activation switch with additional external foot switch control jack
  • fixed level 5.1 DAC output for direct audio transfers
  • optional downmix module supports all standard Dolby mix ratios
  • optional AES Loop-thru feature provides four AES digital outputs for passing signals to other devices downstream
  • 5 year transferable warranty on parts and labor
    ANALOG INPUT THD+N @ 0dB gain, 1kHz
    +20dBu out <0.001% (0.00075% typical)
    +10dBu out <0.003% (0.001% typical)
    0dBu out <0.009% (0.005% typical)
    Intermodulation Distortion SMTPE/DIN 4:1 50Hz, 7kHz
    @+20dBu out <0.002% (0.0015% typical)
    @ 0dBu out <0.008% (0.006% typical)
    Frequency Response
    +/-3dB 3Hz - 250Khz
    Dynamic Range
    20-22kHz bandwidth 112dB
    20-22kHz bandwidth and A weighting filter 115dB
    Output Noise 20-22kHz bandwidth, -20dB gain
    High gain mode -89dBu
    Low gain mode -98dBu
    20-22kHz bandwidth and A weighting filter, -20dB gain
    High gain mode -91dBu
    Low gain mode -99dBu
    Phase Deviation
    20Hz to 20kHz < 4
    10Hz to 100kHz < 15
    Crosstalk any channel
    100Hz < 100dB
    1kHz < 100dB
    20kHz < 85dB
    Balanced Input CMRR
    60Hz > 65dB
    1kHz >65dB
    10kHz >60dB
    Gain Range
    Low gain mode (0.5dB steps) -105.5dB to +20dB
    High gain mode (0.5dB steps) -95.5dB to +30dB
    Channel Tracking Accuracy
    Any channel +/-0.05dB
    Maximum Output Level
    Low gain mode (balanced) +15dBu
    High gain mode (balanced) +27dBu
    Maximum Input Level
    Balanced inputs +30dBu
    Unbalanced inputs +20dBu
    Balanced inputs 30k Ohms
    Unbalanced inputs 50k Ohms
    Balanced outputs 300 Ohms
    Minimum load impedance 300 Ohms
    Output Levels
    User selectable (0dBFS) +16dBu / +24dBu
    Fixed output trim range (0.5dB steps) -95.5dB to +30dB
    1kHz, -1dBFS, 20-22kHz bandwidth (44.1kHz) 0.00%
    Dynamic Range
    20-22kHz bandwidth >111dB
    Input Lock Range
    AES3/SPDIF 32kHz to 192kHz
    TOSLINK 32kHz to 96kHz
    ADAT LIGHTPIPE 30kHz 55kHz
    S-Lock Sample Clock Intrinsic Jitter
    20-22kHz bandwidth <25ps
    S-Lock Sample Clock Jitter Rejection  
    1kHz sine jitter -40dB
    S-Lock Supported Sample Rates
    AES3, SPDIF 44.1, 48, 88.2, 96, 176.4, 192kHz
    TOSLINK 44.1, 48, 88.2, 96kHz
    ADAT LIGHTPIPE 44.1, 48kHz
    s-Lock™ Capture Range
    44.1, 48kHz +/- 10Hz
    88.2, 96kHz +/- 20Hz
    176.4, 192kHz +/- 40Hz
    Word Clock / Superclock Input
    Impedance (switchable) 75 Ohms / 1M Ohms
    Minimum Voltage 3V peak to peak
    Maximum Voltage 5V peak to peak
    Word clock frequencies supported 44.1, 48, 88.2, 96, 176.4, 192kHz
    Superclock frequencies supported 11.2896MHz, 12.288MHz (256x fs)
    Power consumption 60W
    Input Voltage 50-60Hz 100, 120, 220, 230-240VAC
    Main chassis IEC 2U 3.5" x 10.5" x 17"
    Remot control unit 1.6" x 8" x 5.25"
    Power supply unit 1.7" x 8.5" x 8.5"
    Main chassis 14.1lbs / 6.4kg
    Remote control unit 2.3lbs / 1kg
    Power supply unit 6.5lbs / 2.9kg
    All specifications are subject to change without notice

    m906 DOWNMIX Operation

    This m906 can be equipped with an optional DOWNMIX module that creates a stereo L+R mix of a 6 channel surround source. All standard Dolby mix ratios can be calibrated by the user for both the center and surround channels. If installed, operation is as followes:

    To toggle the DOWNMIX mode, press and hold the MUTE/SOLO button. Once enabled, the top line of the System LCD will display “DOWNMIX ACTIVE” (the display will toggle between this and the current input setup). Press and hold the MUTE/SOLO button again to exit DOWNMIX mode.

    Once DOWNMIX is enabled, the composite stereo mix is routed to the corresponding Left and Right Control Room Outputs and the surround outputs are muted. Additionally, the downmixed signal is present as the Headphone Left and Right source and the MON->CUE source. The DOWNMIX ratios are variable and adjusted in CAL mode. The factory default settings are as follows:

    CENTER Channel DOWNMIX Ratio = -3.0dB

    LEFT and RIGHT Surround channel DOWNMIX ratio = -6.0dB

    To Adjust the DOWNMIX Ratios:

    1. Enter CAL mode by pressing the CAL switch. The switch LED will begin to flash, indicating that you’re now in calibration mode.
    2. Press the MUTE/SOLO switch. The switch LED will begin to flash.
    3. DOWNMIX will be engaged and the LCD will display “DOWNMIX RATIO – CENTER LEVEL”.
    4. “CAL” will be displayed in the headphone level LED display while the current ratio is shown in the main level LED display.
    5. Rotate the ‘main level/edit’ rotary encoder in a counter-clockwise direction to increase the amount of attenuation. Rotate the encoder in a clockwise motion to decrease the value. Available ratios are --- (mute), -6.0dB, -4.5dB, -3.0dB, -1.5dB, 0.0dB, 1.5dB and 3.0dB.
    6. Press the MUTE/SOLO button again to access the DOWNMIX ratio for the LS and RS surround channels. The LCD will display “DOWNMIX RATIO – LS AND RS LEVEL”.
    7. Once you’re satisfied with the new DOWNMIX ratios, you can select a new function to edit or exit. Exit CAL mode and return to the normal operating state by pressing the flashing CAL switch.

    MUTE/SOLO Functionality with DOWNMIX:

    When DOWNMIX mode is enabled, the SOLO/MUTE buttons function in an alternate fashion. This functionality is very useful for quickly referencing each surround channel’s contribution to a downmix.

    When DOWNMIX is enabled the LEFT, RIGHT and SUB MUTE/SOLO buttons are disabled and the LEFT and RIGHT channels are always ON. The SUB channel is always OFF.

    The CENTER, LS and RS MUTE/SOLO buttons function as follows:

    • When SOLO mode is active, soloing a channel will cause non-soloed channels to be muted (not added to the downmix).
    • When MUTE mode is active, muting a channel removes it from the downmix.

    Our DA and AD converters employ our propriatery s-Lock™ circuit, a two stage PLL (phase lock loop) system to provide practically jitter-free recovered clocks with extremely high incoming jitter attenuation. The first stage is a wide lock range ultra low noise analog PLL, which can lock to incoming word clocks and Digidesign® Loop Sync signals with a +/-8% lock range. Rather than using standard CMOS based PLL chips for the first stage PLL, we use an extremely quiet, discrete VCO (voltage controlled oscillator). When using a quality external clock source, this PLL alone will provide a nearly crystal quality clock. The incoming jitter rejection of this PLL begins at 500Hz and increases at 12dB/octave with rising frequency. The wide lock range allows for the converter to actually operate in vari-speed applications without a sacrifice in audio performance, provided that the external clock source is relatively low jitter.

    When the incoming sample rate is within +/-200 ppm of the selected sample rate, the secondary (our proprietary s-Lock™) crystal based PLL will lock to the first stage PLL, providing the quietest possible recovered sample clock to the converters. The s-Lock™ PLL is capable of extreme rejection of incoming jitter, which begins at less than 0.1Hz and is better than 60dB at 1kHz.

    While it is very easy (and economical) to provide “jitter free” sample clocks by routing the audio data through an ASRC (asynchronous sample rate converter), we believe that the convenience of these circuits does not outweigh the potential sonic degradation caused by additional signal processing. The performance of the s-Lock™ PLL renders even the worst case interface jitter artifacts to a level well below the noise floor of the converter.