Manley Stereo Variable Mu Limiter/Compressor

Tube compressor/limiter with high-pass filter option
Manley Stereo Variable Mu Limiter/Compressor
Manley Stereo Variable Mu Limiter/Compressor Manley Stereo Variable Mu Limiter/Compressor Manley Stereo Variable Mu Limiter/Compressor Manley Stereo Variable Mu Limiter/Compressor Manley Stereo Variable Mu Limiter/Compressor video video
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The renowned Manley Stereo Variable Mu compressor/limiter is a favorite of producers and recording engineers - and one listen to what this device does for your sound will make you a believer, too! Anyone who has heard the classic Fairchild 670 Series limiters in action has an idea of this Variable Mu's capabilities - but the sound is even sweeter with the Variable Mu. Its adjustable attack and release settings are optimized for mixing and mastering, but are flexible for most tracking situations. Sonically versatile and dependable for daily use, the Variable Mu is Manley's best-selling device. 

Manley Variable Mu Compressor/Limiter at a Glance:

  • Classic compression/limiting
  • Perfect for dual mono or stereo applications

Classic compression/limiting
Although the Variable Mu is not a clone of one, the Fairchild 670 series used a similar limiting principle and those who are familiar with that piece of gear know this method to be very special. In fact, with "mu" meaning gain or amplification factor, the Variable Mu offers true variable gain, unlike most devices. How it works is that the unique 5670 dual trioide is at the center of the peak-reducing and compression action - and it's constantly being re-biased by the vacuum tube rectified side-chain control voltages. This causes the tube to smoothly change its gain.

The Varible Mu's Compress mode is soft-knee 1.5:1 ratio while the sharper knee Limit mode starts at 4:1 and moves to a more dramatic ratio of 20:1 when limiting over 12dB. Interestingly, the knee actually softens as more limiting is used. Distortion can be creatively used by turning up the Input and turning down the Outputs while using very little or no compression.

Perfect for dual-mono or stereo applications
You might notice that the Vari-Mu has a ganged input control, but it's certainly not mono-unfriendly. There are separate threshold and output controls to make compensations with, plus you can always adjust your individual source levels elsewhere. The advantage of the stereo input control becomes clear when you switch to Link mode, and that's what th Variable Mu does better than anything else: final mix, 2-track, or mastering limiting and compression. Like one reviewer put it: "It's like pouring a bowl of sweet cream over the mix."


  • Manley input & output transformers with pure nickel laminations in mu-metal case with flat frequency response
  • 20Hz-25KHz frequency response
  • Balanced inputs & outputs
  • Fully differential all-tube circuitry using one each 5670, 5751, 7044, & 12AL5 per channel 
  • Independently regulated B+ and heater supplies 
  • Includes HP sidechain modification as standard
  • Hard-wire bypass switch 
  • Silent conductive plastic input attenuator 
  • Recovery 5 steps: 0.2s, 0.4s, 0.6s, 4sec., 8sec. (Not a 12-step recovery)
  • Variable attack: 25msec-70msec 
  • Continuously variable threshold 
  • Switch for limit or compress modes 
  • Front panel mounted meter adjust 
  • Limit (4:1 to 20:1) or compress (1.5:1) 
  • Large illuminated sifam meters 
  • Stereo link switch 
  • Maximum gain: 35 dB 
  • <0.1% THD @ 1KHz Noise floor: -85dB typical 
  • Max. output +30dBm (26Vrms) 26dB Headroom 
  • Power consumption (120/240VAC): 80 watts 
  • Dimensions: 19" x 3 1/2" x 10" (occupies 2u) 
  • Shipping weight: 23 lbs.

Additional Information

Condition New
Channels Dual-Channel
Chassis 19-in Rackmount
Rack Spaces 2u
Digital I/O No

Like many landmark moments in a person's life, I remember the first time I heard a Vari-Mu. It was right around the turn of the century and a studio client brought one in to my humble little 48-track analog studio with his favorite preamps and mics. We had one of those well-known British consoles with a built-in buss compressor (really, not a bad one at all). You know the one, with the clunky automation. LOL. So the client says, "hey can we bypass that buss compressor and insert my Manley Vari-Mu on the stereo mix instead?" I'd been mixing music for about 15 years at this point and I thought I'd heard it all. Wow, was I wrong! Immediately on first listendown, it was like I had reached Nirvana (the metaphysical state, not the band). Everything in the mix just became "better." The highs were elevated in the most musical luscious way, I'd ever heard, the mids were pushed out front and center with an immediacy and a "snap" that just reached out of the speakers and gently caressed your eardrum, and the lows pushed me back in my chair, becoming the bold anchor of each track. Everything sit perfectly where it belonged, where I had *intended* it to belong, almost as if the Vari-Mu was reading my musical mind and it knew just what to do. There's only one way to describe that: Magic. Pure magic. I bought one two weeks later and am now the proud owner of my THIRD Vari-Mu! Sell your car if you have to, but buy one of these. Buy it now.

By Eric on November 12, 2018

Bought the Vari Mu several years ago. It was one of the first high-end hardware pieces I ever purchased. I love it. Some hardware is sold with the rationalization that there is a cumulative effect as gear is introduced into the signal path. The Manley Vari Mu is NOTICEABLE by itself. I've been stymied trying to understand why a mix wasn't sounding good only to find that I left the Vari Mu out of the hardware chain. I actually phoned EveAnna Manley to say thanks & send my compliments on the Vari Mu. It's the best piece of audio hardware I've ever purchased (really).

By ENW on November 7, 2018

Love it for warmth and the way it subtly brightens the 2-bus!

By Charles-mile on November 6, 2018

It is not a modern classic without reason, it does something that only a Manley Vari-Mu can do. It's heavy, it has a bunch of tube tone. It's not subtle but not too much either. I use it on all style of music. It compress in a very particular way, it feels like it detect vocals better than any other bus compressor I have used, it really blend to vocals in the track and let the music breathe out when you there's no lead. Anyway, it's on my mix bus and I enjoy it.

By mile on November 5, 2018

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