Manley VOXBOX - MVB 1996 - 2/2000 and MVBX 6/2000 - 4/2003 - Manual (Page 11)

THE MIC PREAMP & COMPRESSOR
The VOXBOX can be divided into two main sections. The first is the Compressor and Mic Preamplifier. The
input signal can be a microphone, instrument or line level signal. The mic and line inputs are on the back panel. The
mic input is transformer balanced with 48 volt phantom power available, switched from the front. The line input has
both XLR and 1/4 inch phone jacks and will accept balanced or unbalanced signal at either of the jacks. To use the line
or instrument input, the phase/polarity switch should be set to the middle position to disconnect the mic input
transformer. The instrument input on the front panel will over-ride the line input so to use the line input, you must not
have a jack plugged into the instrument input. You will probably need to really turn up the gain to get a reasonable output
with a guitar. We also suggest that you rely on the limiter in the EQ section rather than compress because the impedance
may lower from 100K ohms to 50K ohms and this eats highs. Whichever input you use, the next thing the signal sees
is the Filter which allows you to cut lows at 80 or 120 Hz to help reduce room rumble or pops. The next thing is the
INPUT control which is the main level adjustment. This is followed by a passive opto-isolator that does the "work"
of the compressor. Up to this point the signal has only gone through passive components - no gain, no clipping, no noise.
The signal then goes to the all tube amplifier which is the standard Manley 40 dB Mic Preamplifier that has been
winning shoot-outs for years. The GAIN switch is not a pad. This control sets the overall gain by setting the amount
of negative feedback. Besides gain, this affects several aspects of the "sound" of a pre-amp including transient speed,
& accuracy, distortion, noise, output impedance and clipping characteristics. At lower gains (40 dB setting) the Pre
Amp has a very clean quality, in some ways like solid state and is the best at minimizing tube hiss. "45" is a normal
setting because it tends to sound most like the source, and is very musical and real. The "40" settings can sound slightly
slower, further back and more mellow by comparison. The 50 dB setting uses almost no feedback and can give a slightly
more punchy and forward or aggressive sound. It may be a little "hot" (more than simply warm) for some tastes.
Experiment to discover your own descriptions. You will likely find a few settings that you prefer for your style of music.
The preamplifier has two outputs. The first is the unbalanced (and transformerless) 1/4 inch phone jack. It interrupts
the signal before the transformer balanced XLR output. Use one or the other, but you can not use both outputs.
A few words about PHANTOM POWER. It is a rare occurance but a few ribbon mics and PZMs can be
damaged by the 48 volts of phantom power. We suggest to ALWAYS have PHANTOM switched off when switching
mics, cables, patches that involve mics etc. You ONLY need phantom power for SOLID STATE (FET) CONDENSOR
MICS. You should have phantom switched "off" for tube mics, dynamic mics, ribbon mics and battery powered mics.
This is true for all mic pre's. With this MIC PRE you "PULL THE TOGGLE to SWITCH PHANTOM". It is a locking
toggle to prevent "accidents". The second great reason for not using phantom if you don't have to is that - if you change
a connection with phantom on, then the preamp will be fed a quick burst of 48 volts (when it normally is amplifying
about a hundredth of a volt), which may be monitored - usually once. After you have replaced your speakers, you have
learned a valuable lesson about turning down the volume of the monitors before changing mics or mic patches. This
is a good habit with phantom on or off. Consider a variation of this - any slightly intermittant mic connection, will be
super noisy with phantom turned on. This goes for cables, patchbays and patch cords.
Suggestion #2 - Avoid running mic signals through patchbays. Some patchbays "ground" all the "sleeves"
which can add a ground loop into your delicate mic signal. Ground loops usually cause hum.
Suggestion #3 - You can set up the VOXBOX in the studio near the mic and use a short mic cable. Why?
Microphones often have "light duty" line drivers and you can lose an audible amount of signal in long cables. You can
get the best fidelity by having the mic pre close to the mic at the "cost" of having to walk into the studio to adjust a level
control. You also avoid almost all of that phantom power / patching problem because now you have the mic plugged
in directly to the mic pre and are patching the hefty line level output at the console.
Suggestion #4 - If it sounds good, no problems - fine - record.
The PHASE switch is very important when more than one mic is picking up a particular instrument. A good
example is a snare drum with a mic on the top and another on the bottom. The two mics are out of phase acoustically
and unless one of the mic signals is flipped 180 degrees one can expect some cancellation of lows. For vocals, we often
assume that the PHASE switch is unimportant (only one mic) and we don't hear a significant difference in the control
room - but the singer will. If the headphones are out of phase with thier own voice, it sounds pretty strange. Flip the
switch - ask them what they prefer. This might explain why sometimes you just couldn't satisfy the singers headphone
complaints. A fair amount of older gear (especially mics) may be pin 3 hot (out of phase) because the pin 2 hot standard
is only a few years old.
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