Recording - August 2017 - 36

Manley
Labs

Nu Mu and
Universal Audio
Variable Mu for
UAD-2 and Apollo
New hardware and new software...
compared to the original Variable Mu

REVIEWS BY PAUL VNUK JR. WITH JUSTIN PERKINS

or the past year and a half we have been getting
acquainted with the newest products from Manley Labs.
Manley's new line uses modern design processes, a new
universal power supply, and standardized in-house
manufacturing to bring classic Manley quality down to a more
affordable level for home and project studios. We've reviewed the
Manley CORE Reference Channel Strip (October 2015), the ELOP+
(April 2017); the line also includes the FORCE 4-channel mic preamp and the unit under review today, the Nu Mu.

We have also had the chance to take a fresh look at a few
of Manley's classic pieces like the VOXBOX and the Massive
Passive, in side-by-side comparisons with Universal Audio's
latest plug-in models of said units (February 2017 and February
2015 respectively).
This month we are going to look at all three offerings in a
particularly famous lineup: the original Manley Variable Mu
compressor, its Universal Audio plug-in counterpart, and the
Nu Mu.

What is Variable Mu, anyway?

All compressors make use of a gain reduction circuit, and
this circuit's behavior directly impacts the sound. Some use a
FET circuit, others an optical cell, and some a VCA design. In
a Variable Mu design, the circuit uses constant tube rebiasing
for its gain reduction.
Manley describe it best: "'Mu' is tube-speak for gain, and
Variable Mu® is our registered trademark for this limiter
compressor. It works by using the "remote cut-off" or re-biasing
of a vacuum tube to achieve compression." One of the most
famous compressors to use this type of tube re-biasing design
is the Fairchild 660/670.

RECORDING August 2017

The Manley Variable Mu

The original Manley Variable Mu is a stereo/dual mono
unit with a soft knee compression ratio of 1:5 to 1 or a sharp
knee limit mode of 4:1 to 20:1, depending on how hard the
threshold is hit. To get a handle on the rest of its controls and
features, let's take a quick tour of the original.
The thick milled front faceplate is home to a pair of mirrored
matching channels, each of which is dominated by a large
Sifam VU meter showing gain reduction. Each channel has
controls for Recovery (release), Output (makeup gain), Threshold,
and Attack. These come in two varieties, either stepped switches
on the mastering version or as variable pots. Note that on both
versions the recovery control is always stepped at 0.2, 0.4,
0.6, 4, and 8 seconds. The attack goes from 25 to 70 msec,
the threshold is fully variable, and the maximum output level is
+35 dB. As mentioned, each channel can be independently
switched between compress or limit mode, and each one also
offers a highpass sidechain Filter (-3 dB @100 Hz).
As for input, this is a vintage-style compressor where you
bring the threshold down to meet the signal you are feeding it.
If done this way, the compression will be a bit cleaner and more
transparent. However, this unit has a well-deserved reputation
for its saturation and distortion characteristics when pushed,
even with minimal or no compression. To aid in this, there
is a single knob in the center of the unit labeled Dual Input,
which pushes or attenuates the signal ±8 dB equally on both
channels. Each channel can be individually hard bypassed,
and the two channels can be linked for stereo use, making the
threshold equally sensitive to the input of both channels.
Around the back, hookup is simple, with a pair of XLR ins
and outs per channel.

T-Bars and tubes

The unit is an all-tube affair with a 5670, 5751 (or 12AX7),
7044 (or 5687), and 12AL5 per channel. Original units made
use of a GE 6386 instead of the 5670. Clean and quiet versions of the GE tubes are all but gone; Manley switched to the
5670, which does offer a similar sound up to 6 dB of compression, which in most mastering situations is more than fine. Beyond that, the unit is described as more "squashed" sounding.
To solve this, the Variable Mu can be ordered with a T-Bar
Mod which uses a pair of 6BA6 pentode tubes wired as single
triode tubes in place of each 5670 or 6386, both of which
are dual triode tubes. If you are keeping score, that's 8 to 10
tubes per unit!

Table of Contents for the Digital Edition of Recording - August 2017