Manley LANGEVIN DUAL MONO MICROPHONE PREAMPLIFIER WITH EQ - Manual (Page 6)

CONNECTING YOUR PREAMPLIFIER
6
Easy - Connect the mic to the Microphone Input XLR, then connect the Line Output to your
tape machine or console. Read on, there are some things to consider.
On the back panel are female XLR's labelled MIC INPUT A and MIC INPUT B. The signal
from the MICROPHONES get plugged in here. Here are a few warnings and suggestions.
These XLR connectors also "send" PHANTOM POWER to the mics. Some mics can be
damaged by the 48 volts of phantom power. A few PZMs and a few ribbon mics have been
known to "fry" when fed phantom power. The suggestion is to ALWAYS have PHANTOM
switched off when switching mics, cables, patches that involve mics etc. You ONLY use
phantom power for PRO SOLID STATE "FET' CONDENSOR MICS. Tube mics, dynamic
mics, ribbon mics and battery powered mics should have phantom switched "off". 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 pre amp will
be fed a quick burst of 48 volts (when it normally is amplifying about a hundredth of a volt),
which can then 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 idea with phantom on or off. Consider a variation of this -
any mic connection just a little bit bad,will be extra noisy with phantom turned on. This goes
for cables, patchbays, patch cords etc. 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. Suggestion #3 - Set up the Mic Pre 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 are patching
a regular line level signal only.
The INPUT & OUTPUTS XLR PINOUTS are:
PIN 1 = CIRCUIT GROUND
PIN 2 = HOT or positive going phase
PIN 3 = LOW or negative going phase
The OUTPUTs are simple and balanced. They will feed balanced inputs but not unbalanced
inputs "correctly". When one is plugged into an unbalanced input, expect a 6 dB loss of
output level. This will occur no matter how you wire the cable. The best way to drive an
unbalanced input with this unit is not to connect to PIN 3 at the output XLR - just use PIN 1
(ground) and PIN 2 (signal). Better to have PIN 3's signal float than short. You may not
notice the 6 dB "loss" because the preamp still has good headroom.
NOTE: The DIRECT INPUT comes in AFTER the INPUT ATTENUATOR. It comes in at
the wiper (output) of the INPUT ATTENUATOR pot into the first transistor. Thus when you
turn down that INPUT ATTENTUATOR you are moving that point closer towards ground
and loading down that DIRECT INPUT. This will indeed affect frequency response. Solution:
keep the INPUT ATTENUATOR UP (fully clockwise) when you are using the DIRECT
INPUT.