Fredenstein F602 500 Series Tube Compressor

The Fredenstein F602 Compressor is a true variable transconductance (often falsely called “variable mu”) high performance tool for professional recording and mastering engineers. The F602 features the original remote cutoff double triode tube used in many vintage designs (Gates, Fairchild, and GE to name a few) called 6386LGP. The signal path is very short and delivers the smoothness you would expect from a great piece of vintage equipment. The innovative transformer-less input circuit yields clarity while the large Lundahl output transformer adds character.

Like the Fredenstein F660A, the F602 uses a DSP to continually monitor the 6386 tube and optimize its operating points. This has several benefits including automatic self-test and calibration, but also makes possible greater control range and much faster gain reduction.

There are rotary controls for; Threshold, Ratio (2:1 to 20:1), Make-up Gain, Mix (Blend), Attack (250 uS to 15.5 mS) and Release (12 mS to 5 S). There are buttons for Bypass (true hard bypass), Hard Knee / Soft Knee, Link (up to 10 units) and Meter Mode (VU or Gain Reduction). The LINK switch is also a standby switch allowing to shutdown the tube circuitry if the F602 is not in use while the rack is still powered, therefore extending tube life.

The astute reader might notice the exceptional attack and release times that no other “vari-mu” compressor even begins to approach. Usually such fast settings would have a side effect of “thumps” as the gain reduction changes, but in the F602 with the DSP adjusting the tube and maintaining near perfect balance the thumps are eliminated.

The MIX control is also interesting. Fully counter-clockwise, a switch engages and only the compressed signal will be on the output. Fully clockwise, another switch engages and only the uncompressed signal (input) will be on the output. Between those extremes, blending is variable, which is typically used to preserve some transients while raising the level of quieter signals. Similarly, when the Release control is fully counter-clockwise a program dependent Auto-Release setting is engaged and when the Threshold control is fully counter-clockwise compression is turned off.

Gain reduction is displayed traditionally with a VU meter and a Clip indicator lights if the output reaches +24 dBu. Buttons light when engaged.

Specifications are more than respectable for this type of compressor. Lower distortion, wider frequency response and lower noise compared to units much more expensive. The high current design and unusually low output impedance allows even the most difficult and complex loads to be driven without sonic impact. The hot rod mu.

Obviously there is some clever design in this little 500 series unit with a vacuum tube, DSP, MCU control, digital attenuators, high voltage regulators, Lundahl transformer, a discrete line driver and high performance analog throughout. It should also be stressed that it is truly properly engineered, thus uses very high quality parts - besides being built like a tank. Expect it to be reliable and professional. Beyond that, the F602 really sounds quite amazing. A pair of them could be your secret weapon for buss compression and mastering and it won't break the bank. A pair in series is also provides for a very tubular tracking option. Think about it.

Due to the high power consumption of about 8W, not all lunch-boxes and racks are suitable for this module. Of course, Fredenstein boxes and racks are well equipped to handle these loads. As all Fredenstein products, the F602 is designed by a German-American team and manufactured in Taiwan.