Grace Design m502 Single-Channel 500 Series Optical Compressor

Grace Design m502 Single-Channel 500 Series Optical Compressor

Grace Design m502 Single-Channel 500 Series Optical Compressor

B&H # GRAM502 MFR # AM502
Grace Design m502 Single-Channel 500 Series Optical Compressor

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Product Highlights

  • Single-Channel Operation
  • Optical Feedback Circuit
  • 3-Position Input Trim Selector
  • 20 dB Range of Makeup Gain
  • Adjustable Attack and Release Times
  • Threshold and Ratio Controls
  • 10-Segment LED Gain Reduction Meter
  • Stereo Linking / External Sidechain In
  • Requires 500 Series Power Supply
  • Made in the USA
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Grace Design m502 overview

  • 1Description

Sporting an optical circuit to accomplish the gain reduction of sonic material, the m502 from Grace Design is a compressor designed for 500 series racks, commonly referred to as “lunchboxes.” It utilizes a balanced, line-level input and output stage, running a signal through threshold, attack, release, and ratio controls, which can all be tweaked to give you subtle and heavy gain reduction, all while preserving the inherent character of the material fed through its circuit.

Routing is possible to link two units, thereby achieving stereo functionality over dual-channel sources. When activating an internal DIP switch on the circuit board, you can also use this input to feed a sidechain signal into the compressor. However, you would need a lunchbox with auxiliary-connection capabilities built into the unit, such as the Radial Workhorse or the Purple Sweet Ten.

A bright 10-segment LED meter provides clear visual readouts of the gain reduction you are introducing into the signal. With its optical feedback circuit, the unit achieves an inherently neutral and open character, and thus, is quite suitable for tracking instruments, including bass, snares, vocals, guitars, brass instruments, and more.

Controls and Features Explained
Input Trim: This switch selects between three input levels: -10, 0, and +10 dB. Select the setting which best suits the level of the incoming line signal and how much compression you require. This setting is interactive with the threshold control, as a higher input level setting will result in a relatively higher threshold setting to achieve the same amount of gain reduction. This control effectively sets how hard you drive the compressor circuit.

Output: This control provides 20 dB of variable level control at the output of the m502. After setting your desired input and threshold levels, you can set the overall output of the m502 with this control. Use it to properly match to the input of your converter, interface, or whatever is next in your signal path. Also, your signal level may have been reduced by heavy compression settings, so this control can also be used to provide makeup gain.

Threshold: The threshold is the level at which the compressor begins to attenuate the incoming signal. A high threshold setting (counterclockwise) will result in only the dynamically highest passages of the signal being attenuated, while everything below that threshold will remained unaffected by the circuit. Conversely, a lower threshold means more of the signal at the input of the circuit will be attenuated, resulting in more compression.

Attack: This controls the rate at which you want the compressor to start the attenuation of the signal.

Release: This controls the rate at which you want the circuit to release its attenuation of the signal.

Ratio: The compressor’s ratio control is used to set input/output ratio of signals above the threshold. For instance, a setting of 3:1 means that if the incoming signal is 3 dB over the threshold level, that signal will leave the compressor around 1 dB over the threshold level. The highest setting of this control is 12:1, meaning that signals far over the threshold setting are reduced by a much higher ratio; this results in more compression. Lower ratio settings will tend to result in lighter compression amounts.

GR Meter: This meter shows the amount of gain reduction being applied by the compressor. The LED’s illuminate top to bottom, with one LED representing 1 dB of gain reduction and ten LED’s representing 10 dB of gain reduction or more.

Link: This feature is used to link two m502 compressors together for stereo bus compression. In this mode, the sidechain signals of both units are summed together into one. To operate in stereo link mode, both modules need to be connected and both set to Link mode. With two units linked, one is the master and the other the slave, with the master’s controls setting the compression threshold, attack, and release of both units. The slaved unit’s threshold control must be set to the highest, full counterclockwise position. Please note, you must set the ratio manually on both units.

Sidechain Control: For connecting a sidechain signal to the m502, you need a 500 series rack which has a provision for an auxiliary input to the module via pin 7, such as the Radial Engineering Workhorse or the Purple Audio Sweet Ten. Connect an unbalanced sidechain signal via the tip of a 1/4” TRS cable to the auxiliary input. This signal will be available for sidechain input via pin 7. This pin must also be switched on at the m502’s PC board DIP switch location S5 SW2, and the S4 SW1 must be switched off, which will disconnect the linked internal audio path from the sidechain input. Normally, the compressor’s sidechain circuit uses the internal audio signal to trigger its response. But in sidechain mode, the sidechain circuit uses the external signal input to determine how the compressor responds. Examples of using an external sidechain signal include ducking and de-essing.

In the Box
Grace Design m502 Single-Channel 500 Series Optical Compressor
  • Limited 5-Year Transferable Warranty
  • Table of Contents
    • 1Description

    Grace Design m502 specs

    Gain Range Input Trim: -10, 0, +10 dB
    Output Trim: -10 to +10 dB
    Compression Threshold Range: -15 to +15 dBu
    Attack Range: 3 to 200 ms
    Release Range: 0.03 to 3 s
    Ratio Range: 1:1 to 12:1
    Gain Reduction: 0 to 20 dB
    THD + N At 0 dB Gain +10 dBu out: <0.002% (1 kHz, 22 Hz to 22 kHz BW)
    Intermodulation Distortion At 0 dB Gain +20 dBu out: <0.007% (SMPTE/DIN 4:1 7 kHz/50 Hz)
    Output Noise At 0 dB Gain: <-84 dB (22 Hz to 22 kHz BW)
    CMRR At 0 dB Gain, 3.5 Vcm: 100 Hz/1 kHz/10 kHz: >75 dB
    Frequency Response At 0 dB, Gain -3 dB: 0.016 Hz to 150 kHz
    Impedance Line In: 24 kOhms
    Main Out balanced: 350 Ohms
    Main Out unbalanced: 150 Ohms
    Link In - sidechain mode: 100 kOhms
    Level Meters Output Peak Indicator: Green: -15 dBu, Red: +20 dBu
    Gain Reduction Meter: 0 to 10 dB Gain Reduction
    Maximum Output Level At 100 kOhm-load, 0.1% THD: +26 dBu
    Power Consumption 120 mA maximum, current required from +16 V and -16 V power supplies
    Dimensions (H x W x D) 5.3 x 1.5 x 6.6" / 13.3 x 3.8 x 16.7 cm
    Weight 0.7 lb / 0.3 kg
    Packaging Info
    Package Weight 1.85 lb
    Box Dimensions (LxWxH) 12.2 x 10.3 x 4.7"

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