Mercury Recording Equipment Company

Mercury 66

All Tube, All Transformer Mono (linkable for stereo) Studio Limiting Amplifier

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 buy 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:

  • 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.

MERCURY 66 BACK PANELThe 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.

MERCURY 66 DC ADJUSTOne notable change on the Mercury 66 is the addition of the DC Adjust Control. 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

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"

The Mercury 66 is my go-to compressor for getting a huge sounding track. I run tracks through the Mercury 66 Every Day because it can bring tracks back to life back that others have cut and left lifeless. With the Mercury 66 I get All of “the Sound,” there's no skimping here, for less than one third the price of an original Fairchild.

Matt Knobel (Lenny Kravitz, Mika, Lauren Hill)

The Mercury 66 has that thick, glommy quality that you just can't get with any other device. It's killer at taming kick drums, beefing up vocals, squashing room mics, giving that magical shimmery sustain to acoustic guitars, etc.

Pete Weiss, TapeOp Magazine

The Mercury 66 has quickly become a favorite of mine at Swamp Raga Studios. Whether its for tracking huge sounding overdubs, making a stripped down song sound full or making any track step through a full mix, the Mercury 66 delivers with amazing smoothness and tone.

In my opinion, the Mercury 66 is the real deal, and can be heard on many of the lead vocal tracks on the new Tedeschi Trucks Band album "Let Me Get By," as well as some lead guitars, flute and upright bass tracks too. The Mercury 66 is the new must have limiting amplifier in our collection, and we rarely consider anything "must have."

Bobby Tis, Engineer (Derek Trucks and Susan Tedeschi)

Mercury 66 Studio Limiting Amplifier MKIV (MKIV Coming Fall 2021)
LIST PRICE: $9,998

240V Version LIST PRICE: $10,998
240V Version US STREET PRICE: $9,898

Mercury M66 Users include: Joe Chiccarelli, Billy Corgan (Smashing Pumpkins), Rhett Lawrence (Kelly Clarkson, Christina Aguilera), Devin Powers (Devin Powers Music, Movie and TV Scores), Scott Humphrey (Rob Zombie, Motley Crue, Bon Jovi), John McBride (Black Bird Studios and Rentals, Martina McBride) and Manny Marroquin, who has used his M66 on mixes for many Gold and Platinum artists including: Alicia Keys, Brandy, Janet Jackson, Monica, Nikka Costa and many others!

Mercury 66 Data Sheet
Mercury 66 Recall Sheet