11
Audio Wiring
Figure 2: Audio Input Connector Wiring
1
2
3
4
5
6
L+
L-
GND
R+
R
GND
Recommended Practices
Connecting Unbalanced Sources
The audio input and output connectors have ground terminals for each balanced line. This permits
use of separate cables (Belden 8451) or more convenient two pair cables that have a single shield
drain (8723).
Refer to input connector wiring, figure 2, page 7.
The “hot” front-end the LX-1 uses a multi-stage “instrumentation amplifier” with a 50K
Ω
load
impedance. The LX-1 should bridge input devices. Most non-reactive devices (solid-state
amplifiers and consumer devices) do not require termination. In some cases termination is
required to maintain correct output level. Source devices that require termination should be
terminated with the proper resistor.
In general, studio systems with self-terminating outputs and bridging inputs are easier to work
with and deliver higher performance. Avoid the use of pads at the input and output of the LX-1.
Pads may reduce total system dynamic range and common-mode rejection.
Balanced sources should be handled as if the LX-1 input is a transformer. Generally, the shield
should be connected to the LX-1 audio input ground terminal and left open at the source end.
Both the LX-1 and the sources should be connected to a secure ground. A
“star” or “transmission” ground system is recommended. That is, there should be only one path
from each device to station ground.
It will be observed in practice that the 100dB plus CMR of the LX-1 will tend to make grounding
and shielding less critical. This, however, is no license to violate good engineering practices. It is
possible, for example, that input lines will have unequal noise voltages induced on the signal legs.
Unbalanced sources present a special case. Since the LX-1 inputs are high impedance, and high
common-mode rejection is maintained even with unequal source impedances, unbalanced sources
should be treated the same as balanced sources.
The best way to connect unbalanced sources, like consumer CD players, is shown in figure 3
below. The + input line is connected to the “hot” side of the source while the - line is connected
the ground of the unbalanced source. The cable shield is tied to the ground terminal of the LX-1
Both the LX-1 and the source should be tied to the same system ground. Only one ground should
be used for each device.