Mercury Recording Equipment / M66 MK 4.0 (120V)

The Mercury Audio/M66 MK 4.0 (120V) uses currently available circuits, vacuum tubes, custom transformers and design ideas to recreate the sonic characteristics, performance and character of the Fairchild 66. [LF]

The Ultimate Limiting Machine
The Mercury 66 is a variable bias style “All Tube & All Transformer Compressor”.

It is very similar to the Fairchild 660, but due to a lack of original tubes and transformers, it is nearly impossible to reproduce its circuit exactly. However, the Mercury 66 uses similar circuits, tubes, custom transformers, and design ideas to reproduce the sonic characteristics, performance, and features.

This product is based on the Fairchild 660 limiting amplifier. It meets the original specifications using currently available parts, but the most important thing is that the Mercury 66 sounds like a Fairchild.

Main Features

- Outstanding tone and musical focus

- No harshness, distortion or noise

- Extremely fast attack time that allows full limiting in 1/5000th of a second

- Variable release time from 0.3 to 25 seconds

- Useful as a limiter or compressor, depending on the program material and control settings

- Reliable and stable (all components operate below their rated maximum)

- All tube, fully balanced (push-pull) transformer-coupled circuitry

- Simple and easy-to-use controls

Circuit Design

Transformer-coupled inputs and outputs (XLR) with no capacitors in the signal path, a single push-pull stage amplifier with high control voltage, never harsh. It performs best as both a limiter and a straight-through amplifier. The control amplifier is fully transformer-balanced.

The attack time is very fast, capturing short transients. The release time operates from 0.3 to 25 seconds. . Three of the six positions have a release time as a function of the program, with quick recovery for short peaks and maintaining the reduction level if the program level remains high.

DC Adjust Control
Notable in the Mercury 66 is the addition of the DC Adjust Control. On the original Fairchild 660, this control was called DC Threshold and was located on the rear of the unit. We have placed this control on the front panel and named it DC Adjust to avoid confusion with the threshold function.

DC Adjust controls the DC (direct current) in part of the circuit, allowing deeper tuning of the functionality and level of compression. It allows you to control how the amplifier responds to the audio signal and how much the compression tubes ""work"", allowing you to process the signal more aggressively or add a softer touch. Turning the DC Adjust on the M66 all the way to the left (counterclockwise) increases the DC and increases the compression (or saturation), while turning it all the way to the right (clockwise) reduces the amount of DC.
The best thing about this feature is that it lets you find that sweet spot in between. We call it the ""Magic Knob."" This knob is what sets the Mercury 66 apart from the original and other compressor and limiter amps.

Attack and Release Times
Position 1 - Attack [ Fast - 0.2 ] Release, in Seconds [ 0.3 ]
Position 2 - Attack [ Fast - 0.2 ] Release, in Seconds [ 0.8 ]
Position 3 - Attack [ Med. - 0.4 ] Release, in Seconds [ 2.0 ]
Position 4 - Attack [ Slow - 0.8 ] Release, in Seconds [ 5.0 ]
Position 5 - Attack [ Med. - 0.4 ] Release, in Seconds [ Auto: 2.0 peaks, 10.0 program ]
Position 6 - Attack [ Fast - 0.2 ] Release, in Seconds [ Auto: 0.3 peaks, 25.0 program ]

■Specs
・Transformers 600 ohm input and Output
・Gain 7 db (no limiting)
・Frequency Response 40 Hz- 15 kHz +/- 1 db
・Noise = -74 dB below OdBm
・THD: = < 1%
・Compression Ratio 1:1 to 1:20
・Attack Time [1] 0.2 ms, [2] 0.2 ms, [3] 0.4 ms, [4] 0.8 ms, [5] 0.4 ms, [6] 0.2 ms
・Release Time [1] 0.3 ms, [2] 0.8 ms, [3] 2 sec, [4] 5 sec, [5] auto 1, [6] auto 2
・Tubes (1) 6BC8, (2) 6V6, 12BH7, 12AX7, EL34, 5AR4 or GZ34, 5751

Rack Size 3U