Fairchild 660 Mono Compressor/Limiter #567 (Vintage)

The Fairchild 660 is a mono version of the 670 variable-mu type compressor, using the vacuum tubes for reduction of gain right in the audio signal path, (no re-routing to a compression circuit). The original design was built around a series of RCA 6386 tubes. Approximately 800 of these were manufactured. The first unit was sold to fellow New Jersey resident Rudy Van Gelder, who made great use of the compressor when cutting lacquer masters for Blue Note jazz records and Vox classical records. The second unit went to Olmsted Sound Studios in New York, where Jimi Hendrix would record a decade later. The third unit went to guitar legend Les Paul, another Jersey neighbor and audio pioneer.

The essence of the Fairchild 660/670 is very fast attack and slow release times. The fast attack was necessary in its role as a broadcast limiter, protecting the transmission tower from explosive transients that could burn up a transformer. This character was also well suited for mastering mono records.

Check out our Pro Audio Hall of Fame to learn more about this legendary piece of gear.

SETTINGS AND CONTROLS

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.

ATTACK TIME

• 0.2 milliseconds in positions 1, 2 and 6
• 0.4 milliseconds in positions 3 and 5
• 0.8 milliseconds in position 4

RELEASE TIME (FROM 10 DB OF LIMITING)

• Position 1: 0.3 seconds
• Position 2: 0.8 seconds
• Position 3: 2 seconds for multiple peaks
• Position 4: 5 seconds
• Position 5: 2 sec, 10 sec for multiple peaks
• Position 6: 0.3 sec, 10 sec for multiple peaks, 25 sec across similar levels

AUTOMATIC FUNCTION OF PROGRAM MATERIAL

• 0.3 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

SPECS

• Input impedance: 600 ohms
• Output impedance: 600 ohms
• Input levels: Normal line levels (+4 or +8 VU)
• Output level: +4 or +8 dBm line (+27 dBm after clipping point)
• Gain: 16 dB
• Frequency response: 20 cycles to 20kc
• Noise Level: 70 dB below +4 dBm
• Limiting Noises: No audible thumps produced
• Intermodulation or harmonic distortion: less than 1% at any level up to +18 dBm output (no limiting); less than 1% at 10 dB limiting and +12 dBm output