Manley Variable Mu Mastering Limiter/Compressor

The Mastering Version of the Manley Variable Mu Limiter Compressor uses expensive Greyhill rotary switches with gold contacts where conductive plastic pots were used. The steps are determined with a large number of 1% precision metal film 1/2 watt resistors. The best conductive plastic pots only have 10% or 20% tolerance. The ten fold improvement in precision helps a great deal in left-right matching.

There is a subtle audible improvement with stepped switches as well. Audiophile HI-FI often uses that technique to wring the last drop of performance out of a preamplifier. And I bet you wanted stepped switches mostly for resets.

The INPUT LEVEL is a five position switch with a generic optimum setting of “0” in the 12:00 position. Each step in either direction is 2 dB. For reference, Unity Gain is “0”. The OUTPUT Attenuators are in half dB steps. Reference Unity is -11.5 or fully counter-clockwise. You might think of these as “gain makeup”.

They are marked technically, in that “0” or fully clockwise has zero attenuation in the circuit. The tube circuit actually has 15.5 dB of gain. The Input attenuator at “0” removes 4 dB and the Output attenuator removes the last 11.5 producing “unity”. With a little compression the “gain make-up” available with the Output Attenuator is very handy.

The Threshold is in half dB steps calibrated to LIMIT mode. In Compress the steps are approximately 1/4 dB. There are 24 steps so LIMIT gets a 12 dB range and Compress has a 6 dB range of adjustment.

In some cases it is common to use the Input Attenuator to find a good starting point. Some Mastering engineers find using the combination of Input, Output and Threshold to achieve a little different “drive”. Another good reason for stepped gains.

The Attack Time has been slightly extended in both directions compared to a regular Variable Mu and divided into 11 steps. The Recovery 5 position switch is exactly the same as a regular Variable Mu.

The switches specifically are like this:

• Input: -4 to +4 in 2 dB steps
• Output: -11 to 0 in 1/2 dB steps (24 detents)
• Threshold: -11 to +1 in 1/2 dB steps LIMIT(24 detents) and 24 x 1/4 dB steps in COMPRESS
• Attack: 11 positions CW (fast) 15mS, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90mS (slow) CCW
• Release: 5 positions CW (fast) 200mS, 400mS, 600mS, 4S, 8 Seconds (slow) CCW

Proudly from our beginning, we at MANLEY LABS have been closely involved with numerous mastering facilities around the world.

For these most demanding engineers in our industry, we have created specialized products such as our all-tube tape repro head amps, digital converters, high-powered vacuum tube monitor amplifiers, through to custom monitoring consoles, all the way up to complete facility design and installation.