The Manley Nu Mu Stereo Limiter Compressor uses the special T-Bar mod tube front end of the legendary Variable Mu®with same super smooth side chain and timing characteristics followed by a high voltage discrete and FET solid-state amplifying and output stage for a faster and punchier audio path.

The Features
1. OUTPUT CONTROL. The OUTPUT control adjusts the output level on both the L and R channel. 
2.THRESHOLD CONTROL. The THRESHOLD control is available on both the L and R channels. THRESHOLD or gain reduction sets the necessary amplitude for compression or limiting to take effect.
3.COMPRESS / LIMIT SWITCH. Allows the Nu Mu to use two different compression ratios, compressing at approximately 3:1 when the switch is engaged, or limiting at approximately a 10:1 ratio.
4.IN / BYPASS SWITCH. The BYPASS switch is a ‘Hardwire’ bypass for maximum performance. 
5. VU METER. The  VU meters allow easy tracking of both channels and shows the amount of gain reduction in dB from the 0 dB mark, when set to REDUCTION. When O/P is selected, the meter measures the output in decibels.
6. HIP CONTROL. The "Hip" control allows compression at lower volumes but leaves the louder dynamics alone while still compressing the overall signal.
7. METER SELECT SWITCH. The Meter select switch allows the user to monitor either Gain Reduction or the Output of the unit. When the switch is engaged and illuminated, the output of the particular channel you are monitoring is visible in the corresponding VU Meter.
8. ATTACK CONTROL. The ATTACK control determines how long the compressor takes to respond to signals above the threshold. The Attack control is continuously variable and determines the necessary length of a transient to initiate gain reduction.With 63% gain reduction: SLOW 0.13s, MID 0.07s, FAST 0.013s.With 90% gain reduction: SLOW 0.64s, MID 0.35s, FAST 0.064s.Fully counter clockwise at the slowest setting will prevent most percussive signals from causing limiting or compression. It is available on both the left and the right channel.
9. RECOVERY CONTROL. The RECOVERY control determines how long the compressor takes to recover after the signal falls below the threshold level.With 63% gain reduction recovery, five selections: 0.1s, 0.16, 0.32, 0.64s, 1.7s.With 90% gain reduction recovery five selections: 0.227s, 0.368s, 0.736s, 1.6s, 3.87s.
10. LINK FUNCTION. When The LINK function is used it links the two Stereo channels together. The Left channel controls become the master linking THRESHOLD, ATTACK & the RECOVERY CONTROLS.
11. INPUT LEVEL SWITCH. The Input Level is controlled by a toggle switch. There is an Input Level control for each cannel. Three levels of attenuation are available. +3dB, 0dB and -3dB.
12. HP SC SWITCH. The High Pass Side Chain filter is factory set a 100Hz. When this switch is engaged and illuminated, everything above 100Hz will have the effect of limiting or compression. Useful if you want the bass to come through with full impact and limit or compress everything else.
13. POWER SWITCH. The Power Switch glows a soft blue color when an IEC power lead is connected to the unit. This indicates that the Nu Mu is in STANDBY mode. Engaging the power switch takes the Nu Mu out of standby mode and into warm-up mode. The power switch will illuminate to a brighter blue and the backlit VU meters will start to flash. This warm-up process last 30 seconds, after which the MUTE relays will lift and the VU meters will stop flashing.

The Specs
Manley IRON® input transformers
4 x hand-matched 6BA6 vacuum tubes
Balanced XLR inputs & outputs
Manley HIP function raises soft dynamics without squashing louder passages
MANLEY POWER® High Voltage Switched Mode Power Supply custom designed for our vacuum tube audio circuits
INPUT Level Preset 3-way switches -3dB, 0, +3dB
Continuously variable OUTPUT level controls
Unity Gain set INPUT to "0" and OUTPUT control to 11 o’clock. (Input source Z= 150 Ohms, Output load Z= 100 kOhms)
Maximum input level: (1 kHz Sine, <0.3% THD+N)
-3 = +25 dBu
0 = +21 dBu
+3 = +18 dBu
Maximum GAIN: 13dB
GAIN makeup: 10dB (gain above unity)
Output Headroom: 23dB (referenced to +4dBu)
Variable ATTACK control: 13msec - 130msec
RECOVERY switch 5 steps: 0.1s, 0.16s, 0.32s, 0.64s, 1.7sec.
Continuously variable THRESHOLD controls
Hardwired Relay Bypass Switch
Ratio Mode switches between LIMIT (1.5:1 to 12:1) or COMPRESS (1.2:1 to 3:1)
HP SC: High Pass Side Chain Filter -3dB @ 100Hz @ 6dB per Octave
Stereo Link establishes Left-Master dynamic control for THRESHOLD, ATTACK, and RECOVERY controls
Beautiful illuminated stereo VU meters read Gain Reduction or Output Level
Sidechain INSERT per channel via 1/4" TRS jack TIP=SEND, RING=Return, SLEEVE=Ground
Maximum Output: +27dBu (18Vrms) into 100K Ohm load; +24.5dBu (13Vrms) into 600 Ohm load. (1Khz Sine, < 0.3% THD+N, BW 20Hz - 20kHz).
Frequency Response: - 0.8dB @ 20Hz, -0.5dB @ 50kHz
Total Harmonic Distortion: <0.05% THD+N (1kHz Sine, +4dBu, BW: 20Hz - 22kHz)
Noise floor: -85dB typical (BW: 20Hz - 22kHz)
Dynamic Range: 112dB
Signal to Noise Ratio: 89dB (referenced to +4dBu)
Common-Mode Rejection Ratio (CMRR): 74dB (BW: 20Hz - 22kHz, +4dBu, 1kHz Sine)
Output Impedance: 100 Ohms
Input Impedance: -3dB= 1 kOhms, 0dB= 2.5 kOhms, +3dB= 4.5 kOhms
AUTOMUTE warmup delay: 30 Seconds
Power consumption: 35 Watts
Standby Power Consumption: 0.5 Watts
Operating mains voltage: 90 to 254 VAC (internal universal supply)
Mains Voltage Frequency: 50-60Hz
Dimensions: 19" x 3 1/2" x 7" (occupies 2u)
Unit Weight: 8.5 lbs.
Shipping weight: 11.5 lbs.
 

NOTES FROM EVEANNA MANLEY:"So: taking the smoothest & best version of the Variable Mu -the T-BAR mod where we use two 6BA6 Pentodes strapped as triodes to achieve characteristics just about identical to the revered 6386 tubes of the original version (or the Fairchild) -we have the same front end as the Variable Mu. From there we then go into high voltage discrete transistor and FET amplification and drive circuitry. No chips! So this is, yes, less expensive than the all-tube Variable Mu;and also being transformerless on the outputs, very much the clean version of the Variable Mu."Let’s think back to the early 1990’s when the Variable Mu first came out. Recording was a different world. There was still plenty of recording to tape occurring in the big studios. And then digital was not really excellent yet. It was flat sounding and a bit "glary". A big round heavy-handed vibey sound like The Variable Mu was exactly what was needed then. Skipping forward to today, we have really excellent digital converters, and of course it is our de facto standard now. So we don’t need this big masking sound for everything we are doing today, especially for electronic music / EDM where we want to retain super crisp and punchy sounds. We don’t want to add more vibe or slow down the sound. Thus a clean, fast and punchy solid state limiter compressor is what the world needs now. And here is what we have with the Manley Nu Mu – and for all of our individual musician and home recording customers, it is very well-priced for them."