Studio Technologies 50 2005 - Manual (Page 30)

Issue 7, August 2005 Model 50/51 User Guide
Page 30 Studio Technologies, Inc.
Input Data LEDs
The Model 50 Central Controller’s front
panel contains two LEDs that represent in-
coming data. The Bus LED lights any time
valid MIDI-compatible data enters the unit.
The Model 50 LED lights only when data
is received that is valid for the Model 50.
The Model 50 uses MIDI system-exclusive
messages to perform all operations. When
the Model 51 Control Console is con-
nected to the Model 50, both data LEDs
will light any time the Model 51 generates
data. This is because the Model 51 will
only generate data that is compatible with
the Model 50.
If you are not using the Model 51, and
instead are supplying MIDI data using
another device, the LEDs should prove
extremely useful when troubleshooting.
Once the Model 50 is connected to a
data bus that is carrying MIDI data, the
Bus LED will light whenever any MIDI
data is received. Only when the MIDI data
conforms to the Model 50’s MIDI system-
exclusive format will both the data LED’s
light. If the Bus LED lights, but the Model
50 LED does not, this indicates that the
data is not configured correctly for the
Model 50. Refer to Appendix A, located
at the end of this guide, for details on how
data must be sent to the Model 50.
Clicks in the Audio
As covered in the Configuration section
of the guide, the seven stereo line inputs
can be configured for –10 dBV or +4 dBu
operation. Setting an input for –10 dBV,
while connecting an audio source with a
+4 dBu nominal level will lead to distortion
(“clipping”) of the signal. In this fault con-
dition the user would hear a harsh “click-
ing” sounds in the audio, especially when
peak levels occur in the program material.
To remedy this problem simply use the
Model 51 Control Console to configure
the input for +4 dBu operation. The distor-
tion will go away and the gain structure of
the StudioComm system will be correctly
established.
Technical Notes
Talent Amplifier Cable Length
There are no hard and fast rules defining
the maximum cable length when con-
necting Model 35 Talent Amplifiers to the
Model 50 Central Controller. The maxi-
mum cable length is directly related to the
amount of resistance in the connecting
cable; the lower the resistance per foot
(or meter), the longer the cable can be.
(Although cable capacitance affects high
frequency performance, resistance is the
limiting factor is this case.)
To lay out the facts in grammar-school
story problem format: for correct opera-
tion, a Model 35 needs to see at least
+20 Vdc between pins 1 and 2 of their
input connector. The Model 50’s talent
amplifier output voltage across pins 1 and
2 is +23 Vdc, with a maximum current
draw of 0.2 A (200 mA). This difference
between the voltage supplied and the volt-
age required results in a maximum volt-
age drop of 3 V over the interconnecting
cables. Since cable is rated in ohms per
1000 feet (or ohms per 1000 meters), you
need to know what the maximum cable
resistance is. This can be easily calculated
by dividing the maximum voltage drop by
the maximum current flow: 3 V divided by
0.2 A = 15 ohms. For example, a stan-
dard 20 AWG microphone cable is Belden
8412, which has 10.9 ohms resistance
per conductor per 1000 feet. Since we’re