Manley
Manley STEREO VARIABLE MU Mastering
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Manley Stereo Variable Mu Mastering Version is the valve compressor with every continuous potentiometer replaced by stepped Grayhill switches built with 1% metal film resistors. The audio electronics remain unchanged.
Stepped settings instead of potentiometers
Mastering an album means returning to the same setting over several weeks, and a revision a month later has to reproduce it exactly. A continuous knob cannot deliver that: there is always a margin of judgement by eye. In the mastering version every control has detents and a position number, so you write the setting down and come back to it with nothing lost. The same applies to channel matching: left and right are set identically, without trimming against the meters. The 1% metal film resistors on sealed gold Grayhill contacts hold that match after years of use.
The valve itself as the gain control
A variable mu circuit has neither a VCA nor an optical cell. Gain changes through the bias voltage of remote cutoff valves, so the reduction is not applied to the signal, it is how the amplifying stage behaves. That produces the characteristic response: the harder you push it, the gentler the curve looks, instead of a hard knee at the threshold. The mode switch gives 1.5:1 in Compress and 4:1 to 20:1 in Limit, attack is continuously variable from 25 to 70 ms, and recovery has five settings: 0.2 s, 0.4 s, 0.6 s, 4 s and 8 s. A high pass filter in the sidechain at -3 dB @ 100 Hz keeps the low end out of the detector so the kick does not drive the whole mix.
KEY FEATURES
- Mastering version with stepped Grayhill switches
- 1% metal film resistors on sealed gold contacts
- Full recall and exact matching of both channels
- Two channel compressor and limiter with an all-valve path
- Compress mode at 1.5:1 and Limit mode from 4:1 to 20:1
- Attack continuously variable from 25 to 70 ms
- Recovery in five steps: 0.2 s, 0.4 s, 0.6 s, 4 s and 8 s
- High pass filter in the sidechain at -3 dB @ 100 Hz
- Manley IRON transformers with nickel laminations
- Channel linking for stereo operation
- Hardwire bypass for comparison against the unprocessed signal
- Illuminated Sifam gain reduction meters
TECHNICAL SPECIFICATIONS
- Variable gain valves: 5670 x2 in the standard version
- Amplifying valves: 5751 or 12AX7 x2
- Output valves: 12BH7 x2
- Sidechain rectifier: 12AL5 x2
- Frequency response: 20 Hz to 25 kHz (±0.1 dB)
- Maximum gain: 35 dB
- Maximum output: +30 dBu with 26 dB of headroom
- THD: below 0.1% at 1 kHz
- Noise floor: -85 dB typical
- Balanced inputs and outputs, 600 Ohm
- Controls: stepped Grayhill switches with 1% metal film resistors
- Dimensions: 19 x 3.5 x 10 inches, 2U; power consumption 80 W
