Fairchild 660 Mono Compressor/Limiter #274 (Vintage)

The Fairchild 660 is the mono version of the legendary Fairchild 670, a variable-mu type compressor, using vacuum tubes for reduction of gain right in the audio signal path, (no re-routing to a compression circuit).

Controls include a stepped Input Gain and continuously variable Threshold control, as well as a stepped 6-position switch for Attack and Release, that allow for four different combinations and two program-dependent settings. Set-screws on the back of the unit control the ratio; anywhere from 2:1 as a compressor to 30:1 as a limiter.

Controls

• Input Impedance: 600
• Output Impedance: 600
• Input Levels: Normal line levels (+4 or +8 VU)
• Output Level: +4 or +8 dbm line (+27 dbm after clipping point)
• Gain:16db
• Frequency Response: 20 cycles to 20kc
• Noise Level: 70 db below +4dbm
• Limiting Noises: No audible thumps produced
• Intermodulation or Harmonic Distortion: less than 1% at any level up to +18dbm output (no limiting); less than 1% at 10db limiting and +12dbm output

Attack time (adjustable)

• .2 milliseconds in positions 1, 2 and 6
• .4 milliseconds in positions 3 and 5
• .8 milliseconds in position 4

Release time (from 10db of limiting)

• Position 1: .3 seconds
• Position 2: .8 seconds
• Position 3: 2 seconds for multiple peaks
• Position 4: 5 seconds
• Position 5: Automatic function of program material: 2 seconds for individual peaks, 10 seconds for multiple peaks
• Position 6:

Automatic function of program material:

• .3 seconds for individual peaks
• 10 seconds for multiple peaks
• 25 seconds for consistently high program level.

Compression Ratio:

• A function of the amount of limiting as well as setting of the two threshold controls which can be set to operate at ratios from 1:1 to 1:20

Controls:

• Input Gain control Step attenuator; 1 db per step
• Threshold Control continuously variable
• Time Constant Switch 6 positions, so as to provide fixed and variable time constants for any type of program material.
• Metering Switch 3 positions, so as to measure plate current of each of the control tubes, or as a limiting indicator
• On-Off switch

The Fairchild 670 is the grandaddy of all analog compressors. Used on too many famous recordings to list, this was a studio mainstay throughout the heyday of vacuum tube equipment in the 1950s and 60s. Its use in Bill Putnam's United Western Recorders alone accounted for numerous hit records. The single channel 660 model was used extensively at Abbey Road during the Beatles tenure.

Visit our Fairchild 660/670 page for more information.

VARIABLE-MU® is a registered trademark of Manley Laboratories, Inc.