AnaMod® 670 Stereo Limiter

Classic Variable-Mu compression profile and vintage tone

AnaMod 670

  • Three modes of compression and limiting
  • Six original 670 time constants plus two new variations
  • Additional option to operate in true stereo
  • All analog—no latency or digital conversions
  • 3U rackmount form factor

The Fairchild 670 limiter is the most famous and sought-after stereo compressor ever made. The magical way it adds density and dimension to a track or a mix has been demonstrated on many of the best-sounding records made in the last 50 years. For buss compression, the 670 Limiter is the standard by which all others are judged.

Using the AnaMod Process™ to model the complex transformer and tube interactions of the vintage hardware and re-implementing it entirely with analog components, the AnaMod 670 delivers a faithful recreation of the classic unit's sound and compression action. Unlike digital plug-ins or DSP-based outboard gear, there's no latency and no A/D or D/A conversions to compromise the sound.

Like the Fairchild 670, the AnaMod 670 provides Left/Right (dual mono), and Lat/Vert (M-S encode/decode) modes of dynamics processing. It adds a true Stereo mode, which links sidechains of the two channels.


“Any fears that somehow the modelling process might not match the magic of valves are unfounded. Despite my gushing praise for the ATS-1 a year ago, I was still unprepared for how breathtaking the AnaMod 670 sounded. Stunningly and magically authentic Fairchild sound. No latency.” —Resolution

AnaMod 670 Specifications

  • Input Impedance: 20 kΩ, balanced
  • Output Impedance: less than 50 Ω
  • Input Gain: -15 to +15 dB
  • Max. Output Level: +27 dBu, balanced
  • Frequency Response: +/- 1 dB from 40 Hz to 15 kHz
  • Noise Level: better than 73 dB below +4 dBu, 0-30 kHz
  • Limiting Noises: same level as a vintage 660 with GE five star 6386 tubes and properly balanced
  • Total Harmonic Distortion: level- and compression-dependent matching the original unit
  • Compression Ratio: Variable from 1: 1 to 20:1, level-dependent

Automatic Gain Control (AGC) Modes

  • Left/Right: Dual Mono (split) operation
  • Stereo: Left and Right channels are linked
  • Lat/Vert: Left and Right channels are Mid-Side (M-S) encoded, compressed separately, and decoded back to Left/Right

Time Constants

Positions 1-6 are the original time constants. 2a and 2b are variations on #2.

Attack Time
Release Time
0.2 ms
0.3 s
0.2 ms
0.8 s
0.2 ms
1 s
0.2 ms
2 s
0.4 ms
2 s
0.8 ms
5 s
0.4 ms
Auto, as in 660 #5
0.2 ms
Auto, as in 660 #6


  • Power: 120 or 240 VAC (determined at factory), 25 W
  • Dimensions: 3U enclosure, 19" x 5.25" x 7.5" (48.2 x 13.3 x 19.1 cm)
  • Weight: 9.1 lbs (4.1 kg)