Manley Stereo Variable MU Compressor

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Product Code: 9999-09018
Manley Stereo Variable MU
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Manley Stereo Variable MU Compressor

The Manley Stereo Variable MU Compressor is one of the very few compressors that has become a real standard in recording studios and contributed to most hit records over the last decade and probably the next!

The Variable Mu Limiter Compressor is the GLUE that holds the mix together while crystallizing it into a professional, final product. All-tube, all transformer, an all-American legend. High Pass Side Chain mod now comes standard. The Variable MU  has been Manley's best selling product for many years. It is one of the very few compressors that has become a real standard in Mastering studios and contributed to most hit records over the last decade and probably the next. "Mu" is tube-speak for gain, and Variable Mu is Manley's registered trademark for this limiter compressor. It works by using the "remote cut-off" or re-biasing of a vacuum tube to achieve compression. The precious vintage Fairchild 670 also uses this technique and is one of few all-tube compressor to do so, that we know of. Even the side-chain has glowing rectifier bottles. How’s it work? The unique 5670 dual triode is at the center of the peak-reducing and compression action constantly being re-biased by the vacuum tube rectified side-chain control voltages which cause this tube to smoothly change its gain. Just like that.

The COMPRESS mode is soft-knee 1.5 to 1 ratio while the sharper knee LIMIT mode starts at 4 to 1 and moves to a more dramatic ratio of 20 to 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 Output while using very little or no compression. See the gain reduction curves here!

You might notice that the Variable Mu® Limiter Compressor has a ganged input control, but do not jump to conclusions that it is mono-unfriendly. Track away! There are separate threshold and output controls to make compensations with plus you can always adjust your individual source levels elsewhere, right? The advantage of the stereo input control becomes dramatically clear when you switch to LINK mode, and that’s what our Variable Mu® Limiter Compressor 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.” Mmmmmm. Yummy. Give your music a big hug.

The filter is a very gentle 6db per octave 1 pole filter, and will typically be down 1-3db at 100 Hz, and down 4-6db at 50Hz. As you decrease the frequency the amount of limiting will decrease also. At the extreme LF (less than 20Hz) there should be very little gain reduction going on. The whole intent of the filter is to keep very LF stuff (like a heavy kick drum) from activating the compression/limiting so that the overall level doesn't duck with every drumbeat. We can add the High Pass Side Chain option stock boards for an extra $200 NET to older Manley Variable Mu limiters. Units which are more than ten years old that have to be hand wired for this mod will cost slightly more in order to install the circuitry, approximately $275.

Surround Sound Linking Mod
Another mod which can done for several Variable Mu's is to accommodate Surround Sound Linking. This presumes you want to use 4 to 6 (or more) channels of Variable Mu for your 5.1 surround work, and you own two or three Stereo Variable Mu units (or more). For this we add a pair of RCA jacks on the back of each unit so that the sidechain can be easily plugged into another one or two other Stereo Variable Mu units. Then the LINK switch is replaced with a three-way switch and wired to select amongst the following three conditions:

The High Pass Side Chain mod comes stock on all Manley Variable Mu limiter/compressors since 12/2009, on both regular and mastering versions. This mod adds two switches to the front panel, one for each channel, so that when engaged, the side chain will not respond to frequencies lower than 100Hz. (Manley standardly uses 100Hz as the -3dB point. Other frequencies can be custom ordered.) This HP SC Mod can be used with music with heavy bass lines or bass-heavy mixes where you don't want the bass driving the whole action of the compressor.

  • LINK: Link the side-chains of the two channels in this chassis
  • EXT: Link the side-chains of the two channels in this chassis AND to the other units plugged into the RCA linking sidechain access jacks on the back of the unit
  • SEP: Do not link to any other channels

Manley adds TWO RCA jacks to each unit for easy daisy-chaining. Just use any ol' RCA cables you have lying around to link up the sidechains. Then all the sidechains track each other. You still have to set up each unit as you would though, as the very act of linking the side chains does not create a master-slave situation. Manley usually charges $200 NET (per unit) to do this Surround Linking mod.

Mid/Side (Vertical/Lateral or Sum Difference) Mod
Manley also offers a Mid/Side mod upgrade (aka. Vertical/Lateral or Sum/Difference) to the Variable Mu Limiter Compressor which opens the door to stereo encoding and decoding as well as exciting image enhancement processing capabilities. For instance, setting to compress only the in-phase information allows the augmentation of the stereo image as the out-of-phase content is left untouched. Or, conversely, if you need a "more-mono" mix for broadcast, or vinyl-cutting for instance, you can set it to kill off more of the out-of-phase info which leaves more in-phase material in the final result. Read more about the MS Mod on page 12 of the Owner's Manual.

*In order to add both M-S and the HP SC mods, Manley moves the power switch to the rear panel and they install both channels' HP SC switch to the center hole where the power switch was. The M-S switches then flank this switch. Please inquire with us personally for detailed information.

Standard Variable Mu with 5670 Tubes
Yes, the newer base units use the 5670 tube instead of the 6386 used in the original "silver face" Variable Mu. The availability of the original USA GE 6386 is poor; Manley doesn't have any left at all, and what can be found are not usable due to noise, microphonics, bad side-to-side match, etc. Hence the need to change things up a few years back. Newer Manley Variable Mu Compressors use the 5670 tube instead of the 6386. In terms of sound, up to about 6db of limiting it's about the same for these two tube types. After that point, the 5670 version tends to sound more "squashed" than the original 6386 version. Some like it better, some don't-- depends on what you're trying to do. To solve all these problems, Paul at Manley came up with a really good solution: The T-Bar Mod.

T-Bar Mod
The T-Bar Mod uses a pair of 6BA6 pentodes wired as single triodes to replace each dual triode 5670 (or 6386). the 6BA6 TBAR Mod is the preferred system to use in the Manley Variable Mu for reasons of ability to perfectly match each phase-halve section and each stereo set, ability to select for lo-noise and lo-microphonic sets for a low cost, and because the action of the 6BA6's so closely resemble the smooth 6386 limiting curves. In other words, the T-Bar Mod converts later 5670 units to have the same limiting characteristics of the original 6386 for smoother operation.

What is the difference between turning up the INPUT level control to drive the unit into limiting with more level versus using the THRESHOLD control?
The limiting characteristics shouldn't change much, but the distortion characteristics will. The input control on these units is located ahead of the tubes, directly "behind" the input transformer. So as you advance the input control, you're hitting the input tube (which is the gain-varying stage) with more and more signal. Gain reduction is done by making the DC bias on this tube more negative (the threshold control determines how much). The tube has a limit as to how far it can be biased negative to reduce gain before it goes non-linear, and since your audio signal is obviously swinging both positive and negative, the big swings of the audio signal plus the negative gain control voltage will eventually push the tube into the red zone. Tubes like the 6386/6BA6/12BA6 can be pushed a lot farther before the THD builds than tubes like a 5670. Higher signal level also pushes the rest of the tubes and the output transformer harder, which will change the sound character as well.

Manley Stereo Variable MU Compressor Features

  • MANLEY input & output transformers with nickel laminations in mu-metal cases with flat frequency response from 20Hz-25KHz
  • Fully differential ALL-TUBE circuitry using one each 5670, 5751 (or 12AX7), 7044 (or 5687), & 12AL5 per channel
  • Independently regulated B+ and Heater supplies
  • Hard-wire BYPASS switch
  • Stepped switch INPUT attenuator as of 10/2011. (older units use Silent dual-ganged potentiometer)
  • RECOVERY 5 steps: 0.2s, 0.4s, 0.6s, 4sec., 8sec.
  • Variable ATTACK: 25msec-70msec
  • Continuously variable THRESHOLD
  • LIMIT (4:1 to 20:1) or COMPRESS (1.5 to 1)
  • HP SC: High Pass Side Chain Filter -3dB @ 100Hz
  • Large ILLUMINATED Sifam METERS (older units before serial number MSLC61642 shipped before 12/2003 use: 26V 1.2W FESTOON LAMPS; Manley's Part Number: VAR016B) Order spare bulbs using our parts order form. (newest units after serial number MSLC61642 shipped after 12/2003 use white LED lighting)
  • Several units can be linked for Surround (custom order )

Manley Stereo Variable MU Compressor Specifications

  • Maximum gain: 35dB
  • Max. output: +30dBu (26Vrms) 26dB Headroom
  • <0.1% THD @ 1KHz Noise floor: -85dB typical
  • Power Consumption (120/240VAC): 80 watts
  • Unit is factory set for 100V, 120V or 220-240VAC operation for original destination country's mains voltage.
  • Operating Mains Voltage changeable with power transformer changeover switch and fuse value change.
  • Mains Fuse Value for 100~120VAC operation:replace with 1.25A as of 10/2011
  • Mains Fuse Value for 220~240VAC operation: replace with 0.6A (600mA) as of 10/2011
  • Mains Fuse Type: MDA or MDL SLO-BLO Time delay 1 1/4" x 1/4"
  • Mains Voltage Frequency: 50~60Hz
  • Dimensions: 19” x 3 1/2” x 10” (chassis occupies 2u) Power transformer protrudes 3.5" out the back of the chassis.
  • Shipping Weight: 23 lbs.

Manley Stereo Variable MU Compressor Includes

  • Manley Stereo Variable MU Limiter Compressor
  • High Pass Side Chain installed
  • Manual & Literature & Extended Warranty Information (5 Years when registered online)
  • IEC Power Cable
  • Heavy Duty Shipping Box (save this!)

What We Think - Manley Stereo Variable MU Compressor Review

The Manley Variable Mu is a longtime favorite of mine. There's definitely a weighty sound possible from these and the Variable Mu is particularly good and showcasing a vocal when compressing a mix. One of the favorite techniques of recording and mix engineers with the Variable Mu is to cascade signal from one channel to the next in a Compressor > Limiter configuration. This can make any element sound totally in-your-face with a bit of dynamic movement still sprinkled in to taste. It's a favorite on mix bus, vocals, drum room mics, parallel buses, etc. Where can't you use a Variable Mu? When ordering I recommend at least getting the T-Bar mod as it does give a bit more of a smoother transition working into deeper compression since after -6dB the standard valves do sound more squashed. I, personally, like having the additional latitude (a wider sweet spot, if you will) to work with. But if you like that extra-squashy action, the base model certainly won't disappoint.

4 Reviews Hide Reviews Show Reviews

  • 5
    A Studio Classic.

    Posted by Nathan Turnbull on Nov 22nd 2015

    I have had a Manley Variable Mu compressor for about 2 years now. It features Manley branded transformers on the inputs and outputs, and 5670 valves doing the gain reduction.

    It is a high quality unit from front to back. Heavy duty metal work, thick PCB with large traces, plenty of ventilation and easy access for servicing. The panel layout is clear and functional and it sounds amazing.

    The comp/limit switch really makes the unit fun as it has no set compression ratios. The harder you push it, the higher the compression ratio becomes!

    All in all, this unit is a keeper. One of those forever kinds of kit. Get your hands on one and have a play! Here is a cheeky video of some fiddling on a drum bus.

  • 5
    Top 20 of All Time!!

    Posted by KC on Apr 18th 2014

    The Vari Mu is on the list for the top 20 compressors of all time in &quot;Attack Magazine&quot; and that&#039;s the reason why I dropped the cash for it. I kept it because this thing will blow the socks off your mixes.

    Hit this thing hard with your two bus and ease out of it and you will get that &quot;glue&quot; that is instantly recognized in some of your favorite hits of recent times.

    As with all Manley products, this thing&#039;s got mojo...lots of it.

  • 5
    Great across the stereo bus!

    Posted by fanDango on Mar 9th 2011

    This is one of the greatest, most versatile compressors ever made. It sounds cohesive and warm across the stereo bus without being overly intrusive on the sound (bass content stays reasonably intact). Highly recommended! (also very strong on bass and vocal tracks)

  • 5
    This is a Must Have Compressor!

    Posted by jay matheson on Jan 21st 2011

    I have had mine for about 10 years. My main applications have been clean guitars, acoustic guitars, overheads and 2 bus compression. I use my Langevin compressor on bass and vocals It&#039;s a very smooth compressor when used on any source. I wouldn&#039;t use us as a heavy limiter but as a compressor it really sounds incredible. It&#039;s definitely a top shelf unit. It looks feels and sounds incredible.