Description of Block Diagram

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.

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.