The Purple Audio MC77 is a compressor that faithfully recreates the audio circuitry of the revision E 1176, utilizing modern components matched to the original design. The MC77 is designed with a focus on quality, longevity, and flexibility, making it a versatile tool for compression in various audio applications.
Discrete Transistor Audio Path Electronics: The MC77 employs a discrete transistor audio path, ensuring a high-quality signal flow.
Single Element Class A Output Amplifier: The unit features a single-element Class A output amplifier, contributing to its overall performance.
Transformer Balanced XLR Inputs and Outputs: The inputs and outputs are transformer-balanced XLR connections, providing reliable and high-quality signal transmission.
Zener Shunt Regulated Audio Power Supply: The audio power supply is regulated using Zener shunt technology, contributing to stable and clean power delivery.
Compression Ratios: The MC77 offers multiple compression ratios, including 4:1, 8:1, 12:1, and 20:1, providing flexibility for different compression scenarios.
Fast Attack Time: The compressor features a fast attack time ranging from 20 to 800 microseconds, allowing for precise control over the compression envelope.
Release Time: The release time is adjustable, ranging from 50 milliseconds to 1.1 second, enabling customization of the compression characteristics.
Gain of 45dB: The MC77 provides a gain of 45dB, allowing for significant signal amplification without limiting.
Ruggedized Design: The design includes features such as a PCB stiffener and chassis mounts, ensuring durability and robustness.
Purple Anodized Aluminum Front Panel: The front panel is made of purple anodized aluminum, providing an aesthetically pleasing and durable interface.
True Bypass: The unit includes a true bypass function via a sealed relay with a front panel switch, allowing for unaltered signal flow when bypassed.
Improved Stereo Linking: The MC77 includes a front panel switch for improved stereo linking, enhancing its capabilities in stereo applications.
Sidechain Insert Loop or Key Input: The compressor features a front panel switch for selecting between a sidechain insert loop or key input, adding versatility to its functionality.
Buffered VU Meter: The buffered VU meter can monitor either input or output levels at +4dBu, providing visual feedback on signal levels.
LED Meter Lights: The unit includes LED meter lights designed for longevity, ensuring reliable metering over time.
Heavy Gauge Black Cold Rolled Steel Enclosure: The enclosure is constructed from heavy-gauge black cold-rolled steel, providing durability and protection for the internal components.
155V/230V Operation: The MC77 is switchable between 155V and 230V operation, offering flexibility for different power requirements.
Constant Impedance Input Attenuator
Transformer Balanced and Floating
600 ohms at all input gain settings
Maximum Input Level:
+30dBu with limiting active and input cranked up full
(Prolonged exposure to signal levels in excess of +30dBu may burn up the input attenuator)
45dB ±1dB (with limit action switched off)
15Hz to 80KHz ±1dB typical
Floating Transformer Balanced
150 ohms or higher
The Output Level as measured while driving into a bridging load will
drop by no more than 1/2 dB when a load of 600 ohms is added there will be a loss in
Maximum Output Level:
+24 dBm into 600 ohm load (12-1/4 volts RMS)
+30 dBu into bridging load (24-1/2 volts RMS)
Less than 0.5% THD+noise 22Hz-22KHz with limiting activeRelease time set to
1.1sec (fast release times will increase distortion at low frequencies) - NOTE: The VU meter
is now buffered from the audio and adds no appreciable distortion.
>81dB at threshold of limiting 22Hz - 22KHz unweighted
Less than 20µsec for full limiting action
adjustable to 800µsec with front panel control
Minimum 50msec adjustable to 1.1sec maximum (for 63% recovery) with
front panel control
Threshold and Ratio:
With the input control fully clockwise and the output gain control
set 10dB below maximum (at about 6 on the dial)
The overall gain (before limiting) should be 35dB (±1dB)
The threshold of limiting is defined here as 1dB of limiting
at 20:1 the threshold of limiting will occur with an input of -24dBu (±2dB) and yield an
output level of +10dBu
at 12:1 the threshold of limiting will occur with an input of -25dBu (±2dB) and yield an
output level of +9dBu
at 8:1 the threshold of limiting will occur with an input of -26dBu (±2dB) and yield an
output level of +8dBu
at 4:1 the threshold of limiting will occur with an input of -30dBu (±2dB) and yield an
output level of +7dBu
Note: lower ratios make the limiting action kick in sooner
2U 19" rack mounting enclosure (19" wide 3-1/2" high)
Depth behind front panel is 8" (not including connectors)
Front Panel is 1/8" thick aluminium purple anodized
with some variation in color - this can be viewed as a feature and lends a certain
individuality to each unit - Case finish is black powder coat. Legends are silk screened in
12 pounds – loose, 15 pounds – shipping weight.
Start with the customer – find out what they want and give it to them.