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Mercury 66 MK4 - Fairchild 660 Style Mono Limiter (240V Version)

by Mercury
£8,998.99 inc. vat
£7,499.16 ex. vat
Please contact us for availability.

Mercury 66 MK4 - Fairchild 660 Style Mono Limiter (240V Version)

The Mercury 66 Studio Limiting Amplifier [Mk. III] 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.

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.


  • 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"