Fairchild 670

Fairchild 670

Classic Tube Compressor Daily Rate: $250

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Product Info:

The two-channel Fairchild 670 is the "Holy Grail" of compressors in studio gear esoterica, not only because of its price (around $30,000 on the vintage market), but its extreme rareness and the difficulties in maintaining such a piece. With 14 transformers, 20 vacuum tubes, and a 6 rack-space encompassing girth, the 670 is the heavyweight champion of compression weighing in at 65 pounds.


The FAIRCHILD limiter is available in two versions - the monophonic single channel unit, the Model 660, and the unique stereo version, the Model 670. The following basic design points apply to both.


The basic design uses a singl push-pull stage of amplification with an extremely high control voltage. The result: the unit never produces any audible or observable thumps and, unlike other conventionally-designed limiters, the unit has extremely low distortion and noise under all conditions, either as a limiter or a straight through amplifier.


The attack time is very fast - 50 microseconds (1/5000 of a second) - and catches short transients that can, in other limiters, negate the limiting effect. The release time of 3. to 25 seconds provides real flexibility. Three positions (six are available) make the release time a function of program material, fast recovery of program level should the program level remain high.


Ample and accessible input controls, threshold controls, attack and release time and metering controls. The unit can be used as a limiter or compressor, depending upon personal taste and program material. A 2 to 1 ratio as a Compressor with a threshold 5b below average level, and as a peak limiter with a 30 to 1 ratio with a threshold 10 db above normal program level. The unit can also be adjusted to operate anywhere between these two extremes.


Reliability and stability: all components operate well below their rated maximums, insuring, trouble-free performance, and guarantee of day-in-day-out performance results. Masters made one day can be duplicated months later and with the same control settings. Two models are available : the single channel monophonic version, model 660, or the versatile two-channel stereo version, model 670.


In addition, the Model 670 is designed for stereo level control problems specifically. The 670 on one chassis incorporates two independent limiters that will act on left and right channels or which will act on the lateral and vertical (sum and difference) components of the two stereo channels. This latter is accomplished by first bringing the two stereo channels through a matrixing network and then dividing them into their respective lateral and vertical components, limiting these lateral and vertical components and then combining through a second matrixing network into left and right channels again. Using this FAIRCHILD matrix limiter design, thousands upon thousands of stereo masters have been cut with maximum useable level and efficient use of available groove space, resulting in high level recordings with long playing times.This Limit-Matrix system of the 670 now finds the same importance in the new art of stereo broadcasting. No wonder that the FAIRCHILD limiters are used by the major labels and major recording services and quality conscious radio stations throughout the world.


(Each channel, unless otherwise specified)


RANGE OF INPUT LEVEL: 0 dbm to +16 dbm. (-4 dbm to +16 dbm) (model 660) OUTPUT LEVEL: +4 or +8 dbm (+27 dbm clipping point)

GAIN: 7db (16db Model 660)

FREQUENCY RESPONSE: 20 cycles to 15 kc +/- 1db.
SEPARATION: A-B position: 60 db vertical-lateral position: 40 db (does not apply to 660)
NOISE LEVEL: 70db below +4 dbm
LIMITING NOISES: Below audibility
INTERMODULATION OR HARMONIC DISTORTION: Less than 1% at any level up to + 18 dbm output (no limiting) Less than 1% at db limiting +12dbm output
ATTACK TIME: .2 milliseconds on positions 1, 2 and 6 .4 milliseconds on positions 3,4 and 5 (adjustable)
RELEASE TIME: Position 1: .3 sec Position 2: .8 seconds Position 3: 2 seconds Position 4: 5 seconds Position 5: Automatic function of program material: 2 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 1:2 to 1:30
POWER REQUIREMENTS: 115 volts, 50-60 cycles AC, 3 amps.
STABILITY: Unit maintains stability of gain, gain reduction and balance over the range of line voltage fluctuations from 100 to 127 volts.



a) 2 Input Gain controls: Step attenuator: 1 db per step.
b) 2 Threshold Controls: continuously variable.
c) 2 Time Constant Switches: 6 positions so as to provide fixed and variable time constants for any type of program material.
d) 2 Metering Switches: 3 positions so as to measure plate current of each control tube, or as a limiting indicator.
e) Mode Switch: A-B positions: 2 independent limiters. Vertical-Lateral position: matrixing input and output, left and right in and out, limiting action vertical-lateral.
f) On-off switch


MECHANICAL DIMENSIONS: Standard 19" rack, 14" panel space, depth behind panel 11"
WEIGHT: Approximately 65 lbs.
TUBE COMPLEMENT: 8-6386; 1-6084; 1-5651; 2-12AX7; 2-12BH7; 1-EL34; 4-6973; 1-GZ34(5V4).


The model 660 is a single channel Fairchild Limiter. The above specifications apply with the following exceptions: no separation figure needed on the 660; all controls are single, not double as in 670; only half the number of vacuum tubes are used; and an additional 8 DB of gain is available in the 660.



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