Black Box AC1120A User Manual
Model AC1120A, AC1121A, AC1122A, AC1123A
6
The audio input on the basic unit uses standard 3.5mm mini-stereo connectors. To
use these with PC audio, standard male-to-male audio extension cables would be
required. To connect from typical TV sources with separate right and left
connectors, 3.5mm male to 2 RCA cables would be needed.
use these with PC audio, standard male-to-male audio extension cables would be
required. To connect from typical TV sources with separate right and left
connectors, 3.5mm male to 2 RCA cables would be needed.
Technical Note about the Audio Inputs
Since the audio inputs are unbalanced (single ended), the ground reference of
the source has to be the same as the matrix. Of course the cable connecting
the two is tying the grounds across but if there are currents flowing in the
ground it can create potential differences that would manifest as noise. The
quality of grounding at the audio source and the matrix are important. For
example if the input source is a desktop PC, as long as the PC is properly
grounded and the audio cable length is not excessive, you can expect good
results. On the other hand if the input is a notebook PC running on battery,
there is no ground reference at the source so it gets its reference through the
audio (and video) cable connection to the matrix. This should also be okay.
However if it is plugged in through its external power brick, noise can be
induced. This is because most notebook power supplies do not properly
provide an AC ground path to the system ground (some only have only 2 prong
AC cords). The switching power supply circuit will inject noise into the audio
lines. In this case the solution may be to attach a low resistance ground strap
to the notebook. The other option for eliminating the noise is to use a stereo
audio Balun (or isolator). The Balun essentially couples the audio through a
transformer so the audio grounds are isolated. Baluns can also cure noise
pickup in long cable runs.
the source has to be the same as the matrix. Of course the cable connecting
the two is tying the grounds across but if there are currents flowing in the
ground it can create potential differences that would manifest as noise. The
quality of grounding at the audio source and the matrix are important. For
example if the input source is a desktop PC, as long as the PC is properly
grounded and the audio cable length is not excessive, you can expect good
results. On the other hand if the input is a notebook PC running on battery,
there is no ground reference at the source so it gets its reference through the
audio (and video) cable connection to the matrix. This should also be okay.
However if it is plugged in through its external power brick, noise can be
induced. This is because most notebook power supplies do not properly
provide an AC ground path to the system ground (some only have only 2 prong
AC cords). The switching power supply circuit will inject noise into the audio
lines. In this case the solution may be to attach a low resistance ground strap
to the notebook. The other option for eliminating the noise is to use a stereo
audio Balun (or isolator). The Balun essentially couples the audio through a
transformer so the audio grounds are isolated. Baluns can also cure noise
pickup in long cable runs.
2.2 Output Audio & Video Connections
Figure 3 – Standard matrix audio and video outputs
The video output connectors are HD15 female. These are compatible with PC’s
VGA video signal (RGBHV). The Matrix is also compatible with YPbPr HDTV
signals with the use of HD15 to 3 RCA adapter cables.