The second unit went to Olmsted Sound Studios in New York City, and the third 660 built went to Mary Ford and Les Paul.

The mono 660 and dual-channel 670 can function as a compressor with a ratio of 2 to 1 and a threshold of 5 db below normal program level, as a peak limiter with a compression ratio of 30 to 1 and a threshold of 10 db above normal program level, or can operate anywhere between those two extremes.

Both feature an extremely fast attack time that can produce the full limiting effect during the first 1/10,000 of a second.

At the time of its introduction, the 670 was the only unit that could independently control both vertical and lateral with a minimum loss of separation.

[13] Other notable users include: The dual-channel Fairchild 670 was inducted into the TECnology Hall of Fame in 2007.