Manley LANGEVIN DUAL MONO MICROPHONE PREAMPLIFIER WITH EQ - Manual (Page 5)

BASICS
5
This Microphone Preamp, like most mic preamps, is pretty easy to use. First we can discuss why
outboard mic pre's have become "a must have item" in almost every studio even though your console probably
has a bunch of them and that manufacturer claims that they are really great and you don't need outboard mic
pre's. Then, why is everybody buying them, using them, and why are most people going back to tubes or
vintage transistor based circuits?
Good question. The signal from a typical mic is very low - anywhere from 20 to 70 dB below your
normal line level signals. 95% of the time 30 to 40 dB of gain is all that is needed to boost the signal to line
levels. Where you really need a lot of gain is with most ribbon mics and when you are recording chamber
music from a distance. Mic signals are fragile and raw. The fragility is apparent when one compares various
mic pre's - each preamp seems to sound different - no EQ, no compression, nothing elaborate - just basic gain.
Maybe it is the mic reacting different into different circuits. Each preamp, tube or solid state seems to impart
a flavour or color (or personality) of its own. Some of these flavours are subtle and some are not. A few
engineers have an array of mic pre's and use them almost like effects - using each for a certain flavor as needed.
The rest of us only have the budget for one or two great mic pre's so we tend to choose one that sounds "best",
or is priced for us, or is used by "xxxxxx". The Langevin Microphone Preamplifier is superb sounding -
probably because it has a simple all discrete gain stage with a minimum of components and a minumum
amount of negative feedback. Specifications, while important, will not be truly indicative of an audio
product's "sound" until methods of determining the transient accuracy are established. Transient accuracy
is not a "spec" and test benches don't produce hit records. The transient details are important for reproducing
the true character of the instrument, the room and stereo image. Most solid state circuits use a large amont
of negative feedback to lower noise and distortion at the cost of transient accuracy. This preamplifier started
out clean and quiet so minimal negative feedback was necessary.
Op-amp based designs, by comparison, have dozens of transistors in each "chip" (its easier to
fabricate a transistor than a resistor on silicon), hundreds of dB's of negative feedback and sometimes a few
discrete transistors to provide performance that an "IC" simply cannot. The result is good specs - but that
harsh, hard, cold sound that makes shakers sound like pink noise, makes vocals sibilant in an unpleasant way,
and can only render a 2 dimensional image at best. We prefer tubes or simple discrete circuits.
We mentioned mic signals are fragile and raw. Some consider that the "headroom" factor is the most
important issue in mic pre's. We believe that it is just one of a number of issues including the harmonic
character of the distortion. Except for the final output, all circuits are "Class A" which is usually associated
with no crossover distortion and near clipping will be even order distortion and less upper harmonics.This
Preamplifier has more headroom than most solid state mic pre's because of the 48 volt power supply used,
compared to 30 volts (+/- 15V or 24 volts) used in other designs. If overdriven, which is not easy, it starts
to clip in a gentle, smooth way.
Which brings us to the next topic - METERING - We do get questions like "How do I set up the Mic
Pre levels when there are no meters?". Answer - Look at where you are sending the signal, if it has meters
- use them. Why ? Most people are recording to digital mediums where there is no real standard. If you use
the tape machine's digital meters, you will most likely get the best recording levels using the machine's meters.
If we included a meter, it would most likely not be "calibrated" to your meters and mislead or confuse the
user. Also, if we included metering, it would be VU which is a standard of its own appropriate for analog
tape only. Turn up the LEVEL control until the loudest peaks to tape are a few dB below maximum and not
producing "Over" Leds (for safety) and not too low (10 dB below clipping or lower). If we had a "Clipping
LED" for the preamp, it would be probably be dark when the machine's meters were pinned. Cosmetically
a meter might be nice but functionally it would be misleading or mostly useless.