LaChapell Audio 992 Tube Mic Pre - Manual (Page 5)

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Controls:
FIGURE 2.1 the five LED tipped toggles on channel 1 are (from left to right) Meter, 48v, -20db, Polarity Reverse and Mute. The
two lower knobs on the inside are for input gain and the two upper knobs are for output gain.
• INPUT GAIN:
The user is given separate control of the input signal strength via a dual ganged
potentiometer. The pot is placed between the first and second input tube and provides about 20dB of the
>50dB of internal gain; 40dB of the >74dB of internal gain for the extended gain variant.
• OUTPUT GAIN:
Like the input stage, the user is given separate control of the output signal strength via
a custom dual ganged Clarostat potentiometer. The pot is placed between the last input tube and the first
12AU7 output tube and provides all remaining amounts of gain from the input stage.
• POWER TOGGLE:
Controls the on/off power and is slave to the rear main rocker switch located on
the AC PEM.
ƒ NOTE: For best S/N ratio performance with 992 TLS it is assumed the input gain stage is
favored more than the output stage. It is not uncommon for the input pot to be in its’ fully
clockwise position before additional output gain is applied. Use this wisely as too much input
gain (especially with the EG) may result in distortion.
Channel Specific Toggles:
•
METER :
This is a Sifam type AL29WF VU meter and monitors output signal strength. The VU meter is
buffered from the audio path using high impedance precision isolation amplifiers running @40kohm. Use of a
meter isolation amplifier is important for maintaining consistent gain and eliminating IMD regardless of the
meter status (on/off). However, it is strongly recommended that the user switch off the meter when it
becomes ‘pegged’, overdriven. This prolongs the life and accuracy of the meter.
•
48V (Phantom):
48 volts available for condenser microphones. Each 992 is calibrated to exactly 48 volts at
the input jacks at final assembly. It is important that you NOT engage the front panel 48v toggle with
microphones that do not require it: ribbon, dynamic, and tube mics. Applying 48v from any source (not just this
preamp) to some of these microphones can damage or destroy them.