The Fredenstein F660A Limiting Amplifier is a valve (tube) based compressor and limiter with the same very short signal path as the famous Fairchild 660/670. It uses the exact type of tubes, the 6386 LGP, as the Fairchild and 4 of them per channel like the Fairchild.
Fortunately, new production tubes are available today, since original tubes are hardly sold anymore. The four tubes form a single stage push-pull Class A amplifier and the whole signal path consists only of a T-type input attenuator, input transformer, Class A tube amplifier and finally the massive output transformer. At this point the similarities end.
The F660A uses a DSP to control the operating points of the tubes, guaranteeing perfect working conditions all the time. The side chain amplifier is designed with semi-conductor components since it “only” generates the control voltage for the tubes. The final result is a compressor with the compression characteristics of the Fairchild, but with an extended frequency response, lower noise and lower distortion. The perfected tube buss compressor.
The front panel provides immediate access to the most used controls; Make-Up Gain, Compression Threshold, and Release Time. There are 6 Release Time settings designed to mimic the original Fairchild switch. The 3 encoders also function as push buttons for Bypass, Sidechain High Pass Filter and Stereo Link.
The LCD screen is used to set more parameters such as, Attack Time (6 Attack Time settings), Metering range plus choices of RMS, Peak and Hold settings and a Calibration mode. The F660A also allows 99 User Presets to be stored and recalled which is quite a feature in a mastering situation, especially because the F660 self-calibrates for the most part plus has an easy method for complete exact calibration so repeat-ability is a non-issue.
The old Fairchild 660 is a classic compressor with some highly desirable compression characteristics but perhaps some shortcomings with regards to pure fidelity. The F660A combines the sought after character of the original with audio performance well suited for modern production and mastering. But sorry, no maintenance worries, no lost lows and highs, and no old Bakelite knobs and no scratchy pots and switches. It just sounds right.