LaChapell Audio 983s Two Channel Rackmount Tube Preamp - Manual (Page 3)

Controls:
Input Gain
Control
Control Details:
Output Gain
Control
Meter Array
Hi-Z Input
High-Pass Filters
Low-Pass Filters
A/C Power
Switch
Phantom
Power
20dB Input
Pad
Polarity
Reverse
Channel
Mute
Input Gain Control: Provides variable control
over how much input source signal is driven onto
the vacuum tube. Specifically, this control is posi-
tioned after the Jensen input transformer and just
before the 12AX7 tube. Think of this control as
your “throttle” for tube coloration/harmonics
(distortion).
Output Gain Control: Provides variable control
over line level signal strength. Think of this con-
trol as your source for clean gain. Typically, this
control is used to establish the desired line level
after the input gain has been set.
Meter Array: Consisting of three separate seg-
ments: 1) “Sgn”. This is a true microphone input
signal detector, it does NOT display output level.
The LED is calibrated to detect input signals as
low as -50dBu. 2) “+4”. This LED indicates that
line level has been achieved. 3) “Clip”. This LED
is intended to be a warning that clipping may
occur if output signal strength is further pushed.
It is calibrated to illuminate when the output is
driving +23dBu into a 40kohm source; It does not
necessarily indicate that the 983S’s output stage
has reached its limit.
HI-Z Input: This auto-switching hi-z input stage is
transformer-less and operates with an input im-
pendence of 100Kohm. It cannot make use of the
-20dB pad. High-Pass Filters (HP): The 983S provides
both a 50hz cut option and a 150hz cut option.
Low-Pass Filters (LP): The 983S provides
both a 5Khz cut option and 10Khz cut options.
Phantom Power (48v): This toggle provides a
48 volt supply of DC current for all condenser
microphones. Each 983S is calibrated to ex-
actly 48V during final assembly.
20dB Input Pad (-20): When engaged, micro-
phone input source signal is reduced by 20dB.
Specifically, this action occurs before the
Jensen input transformer.
CREATIVE TIP: For
near transformer-less sound, consider engag-
ing this pad function and compensate for the
loss of gain by increasing the input gain con-
trol. This approach effectively minimizes the
gain coming from the Jensen input transformer
while drastically increasing the character of the
vacuum tube (this is only possible with the
microphone path).
Polarity Reverse: Reverses the polarity of the
output line level signal.
Channel Mute: Output level cut-off. LED will
illuminate green when the channel is active.
A/C Power Switch: Master power rocker
switch. LED will illuminate red when power is
on.
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