Mercury M66 – MK IV


Mercury Recording Equipment MERCURY 66 MKIV

The new Mercury 66 Studio Limiting Amplifier is an all tube, all transformer, fully balanced, variable-bias limiter based on the most sought after product in this genre, the legendary Fairchild 660. This limiting amplifier is recognized as an essential tool for making great recordings. Many manufacturers have tried to copy the Fairchild circuit but have failed to capture the sonic essence and overall tone of the original. Until now.

Mercury Recording Equipment has gone to great lengths to recreate the pride and passion of the past, both sonically and aesthetically, while offering the reliability of a modern build. The choices made in looks, layout, functionality, features and build quality all answer back to one question: How would “they” have done it today? So, the Mercury 66, like all Mercury products, has no ICs (chips), and is proudly hand built and assembled in the USA using no-compromise parts/components and has transformer balanced inputs and outputs. With the vintage style VU meter, large bakelite knobs and powder coated chassis and front panel, the Mercury 66 has a very distinctive 1950s aesthetic so that they look as good as they sound!

The Mercury 66 Studio Limiting Amplifier is based on the classic Fairchild 660 limiting amplifier because we were inspired by the unique sound that only this circuit delivers to your audio signal path. Using parts that are available today, we have met all the original specifications, but most importantly, the Mercury 66 sounds like a Fairchild. Its performance features include:

Key Features:

  • Vintage Tone and Craftsmanship, in a Modern, Improved 3U Designed Package… 34lbs. Mono.
  • Exceptional tone and musical focus
  • Absence of audible thumps, distortion or noise
  • Extremely fast attack time that can produce full limiting in 1/5000th of a second
  • Variable release time from .3 seconds to 25 seconds
  • Useful as a limiter or a compressor depending on the program material and control settings
  • Reliability and stability (All components operate well below their rated maximums)
  • All tube, fully balanced (push-pull) transformer coupled circuitry
  • Simple, easy to use controls.

The Mercury 66 Studio Limiting Amplifier uses a single push-pull stage of amplification which are transformer coupled input and output (XLRs) with no capacitors in the signal path, with a high control voltage. The result: the unit never produces any audible thumps, and has low distortion and noise under all conditions (either as a limiter or straight-through amplifier). The control amplifier is also fully balanced, transformer coupled in/out. The unit makes use of a very stable high current vacuum tube voltage regulator. It has ample and accessible input, threshold, attack, release time and metering controls allowing for convenience in the control room when making adjustments. The attack time is very fast and catches short transients. The release time of .3 to 25 seconds provides real flexibility: Three positions of the six available make the release time a function of program material, with fast recovery for short duration peaks and overall reduction of program level should the program level remain high. It can be used as a limiter or compressor. For example, use it as a 2 to 1 ratio compressor with a threshold 5 dB below average level, or as a peak limiter with a 20 to 1 ratio with threshold 10 dB above normal program level, or anywhere between these extremes.

One notable change on the Mercury 66 is the addition of the DC Adjust Control. The Mercury 66 was the first 660 Style Limiter to have this modified feature. On an original Fairchild 660 this was called DC Threshold and was on the rear of the unit (not accessible from front panel). We put that control on the front panel and labeled it DC Adjust to not confuse the Threshold function. The DC Adjust lets you control DC (Direct Current) in part of the circuit to give the user more control of the functionality and level of compression. This gives you the control how the amplifier reacts to the audio signal and basically how hard the compression tube ‘works’, allowing you to smash the signal or just add a soft touch of compression. This is possible by turning the DC Adjust to the far left (counter clockwise) on the M66 to add more DC and more compression [or saturation] — turn to the far right (clockwise) to decrease the amount of DC and the amount compression [or saturation, for a lack of a better term and to make things easier to understand]. The best thing about this feature is you can find that sweet spot in-between. We like to think of this as the ‘magic knob’ as do most of our users and this sets the Mercury 66 apart from the original and other compressors and limiting amplifiers available today.

Front Panel Controls

  • Input Gain
  • AC Threshold
  • Attack/Release
  • DC Adjust
  • Meter Zero (Trim)
  • Stereo Link **
  • Power on/off Switch

** You can connect 2 M66 Limiting Amplifiers together for stereo operation! (special link cable needed)

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 ]
  • 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
  • Weight: 38 lbs.
  • Shipping Size: 25″ x 19″ x 10″