Whirlwind LD410 - Manual (Page 2)

The LD410 is a versatile, multipurpose line driver and multi-channel distribution
amplifier. There are eight input channels and eight output channels. Internal signal routing
jumpers configure the connections between the inputs and outputs. There are three types of
connectors providing access to the unit; male and female XLR and Phoenix style screw
terminals for balanced signals and RCA jacks for unbalanced connections.
After the signal has passed through the input connector, the circuitry of each of the input
channel is identical. Inputs 1, 2, 5 and 6 have female XLR balanced connectors. Inputs 3,
4, 7 and 8 have screw terminal connections for balanced signals and RCA jacks for
unbalanced signals. The tip of each RCA jack is wired in parallel to the corresponding
positive screw terminal and the sleeve of the RCA jack is wired in parallel to the minus
screw terminal. This provides a floating ground for unbalanced signals, which may reduce
ground loop hum in some installations. To ground the sleeve of the RCA jack, connect a
small jumper wire between the minus and the ground on the screw terminals of the
corresponding channel.
From the input connector, the signal passes through a switchable 14dB pad. Maximum
input signal level is +22dB and the pad can be inserted to attenuate higher input levels.
The signal then passes to an input buffer circuit and the high quality, low noise, line level
preamp. The output from the preamp is connected to two pin circuit board headers.
Movable jumpers route the signal to the output line drivers.
The output line driver circuits use the signal routing jumpers to select a signal coming
from the input preamps. Signals from inputs 1 and 2 are available to all eight outputs.
Outputs 1 and 2 have two input choices, outputs 3 and 4 have three choices and outputs 4
through 8 have four possible input signal selections. This flexibility allows the
configuration of many different signal distribution schemes.
DESCRIPTION OF BLOCK DIAGRAM
The standard factory configuration is that of a dual stereo -10dB to +4dB
and +4dB to -10dB level converter. Channels 1, 2, 5 and 6 convert +4dB balanced
signals to -10dB unbalanced. Channels 3, 4, 7 and 8 convert -10dB unbalanced
signals into +4dB balanced ones.
From the routing jumpers, the signal is applied to the gain stage of the output line
driver circuitry and to a clip detector circuit. A front panel gain control provides
up to 38dB of signal gain or attenuation, a range of control sufficient for virtually
any level matching requirement.
Following the gain stage, the signal is delivered to the output buffers, the mute
circuit and the LED level detectors. Each output connector has a separate driver
circuit. This means that on channels 1, 2, 5 and 6, the balanced screw terminal
output and the RCA can be used simultaneously. The mute circuit, activated by a
front panel switch, turns off the signal at the output connector and illuminates the
clip LED to indicate that the output is muted.
The three LED indicators on the front panel monitor signal levels within the
LD410 circuitry. The green -10dB LED and the yellow +4dB LED monitor
output signals after the gain control. The green LED is calibrated to light when
the signal level at the output RCA is at -10dB. The yellow is set to light when the
level at the balanced outputs is at +4dB. The red clip LED monitors the signal
both before and after the output gain stage. This design provides a
troubleshooting tool to help determine whether clipping is being caused by too
much output gain or by excessive input level. If clipping occurs, turn the output
gain down. If the clip LED stays lit, the input signal is too high and the input pad
should be engaged to reduce the level. The red LED is also used to indicate that
the output is muted, it will remain lit when the mute is active.
The power supply for the LD410 is internal and can be set for 230VAC use by
changing internal solder jumpers on the primary of the power transformer.