Among audio professionals, the Fairchild 670 is the most coveted of all compressors, not only because of its unique color and character, but also its rarity and price: With fewer than 100 units ever made, original Fairchilds routinely go for tens of thousands of dollars on the vintage market. With 20 vacuum tubes and 4 hand-wired transformers in a hefty 6 rack-space chassis, these hard-to-find units weigh in at a robust 65 lbs. Both the stereo 670 and its mono counterpart the Fairchild 660 use single push-pull amplification stages with extremely high control voltages. Both variable-mu limiters are unique in that they use tubes for gain reduction as well as amplification. Compression takes place directly in the audio path, rather than being routed to a separate circuit.