Studio Technologies 2A 2013 - Manual (Page 16)

Issue 1, October 2013 Model 2A User Guide
Page 16 Studio Technologies, Inc.
Setting the mode switches and connect-
ing signals is quite easy. Set the telephone
interface mode switches, located on the
back panel, to the desired mode—either
telephone line or standard audio. Use
modular telephone cables to connect to
the Model 2A’s RJ11 jacks. Technically,
the Model 2A’s telephone interfaces use
6-position modular jacks with pins 3 and 4
used for the actual electrical connections.
If the telephone line mode is selected, the
Model 2A’s telephone interface connec-
tions should, in most cases, terminate on
an I/O panel of some type. This will allow
rapid connection with telephone company-
provided lines. Because of the presence of
high-voltage ringing signals, it is strongly
advised to not route telephone lines
through an audio patch bay.
If the standard audio mode is selected
direct connections to a source device is
acceptable. But connecting them via audio
patch points will provide better flexibility.
In the standard audio mode the interface
looks like a transformer coupled audio
input. Interface 1 has an input impedance
of 2200 ohms. Interface 2 has an input
impedance of 2200 ohms in the receive
mode and 700 ohms in the send mode. In
standard audio mode, the interfaces are
compatible with balanced or unbalanced
signals. No shield connection is associ-
ated with the telephone interfaces. If pos-
sible, audio signals should be connected
to the Model 2A’s telephone interfaces, via
a modular plug and cable, using shielded
cable, with the shield wire connected to
the appropriate point at the end opposite
of the Model 2A. The shield wire should re-
main unterminated at the Model 2A’s end.
The telephone interfaces were designed
to receive and, in the case of interface 2,
send audio signals at a nominal level that is
correct for telephone circuits. (This nominal
level is far lower than the typical +4 dBu
professional audio standard.) The receive
signal level is expected to be approximately
–15 dBu and the transmit level approxi-
mately –6 dBu. Trim pots, accessible on
the front panel, are associated with each
telephone interface. This allows the receive
level to be adjusted over a ±8 dB range.
Special precautions may need to be taken
when an interface is set for standard audio
mode and +4 dBu signals are going to be
connected. Including an audio attenuator or
“pad” with a value of somewhere between
10 and 20 dB in series with the source sig-
nal will optimize the receive audio level. In
addition, using a line amplifier or other gain
stage to achieve a higher send level from
telephone interface 2 may be helpful.
Model 22 Access Stations
The Model 2A allows the connection of
up to four Model 22 Access Stations. The
Model 22 provides an unbalanced micro-
phone input, a balanced line-level input, two
lighted pushbutton switches, and related
circuitry. Power is provided by the Model 2A
so an external power source is not required.
A cable with 9-pin D-subminiature male
(DE-9M) connectors on each end links a
Model 2A Central Controller with the first
Model 22 Access Station. Identical cables
are used to interconnect up to three ad-
ditional Model 22 units in a daisy-chain
fashion. A 5-position screw terminal strip,
located on the rear of the Model 22, allows
connection of either a Studio Technologies’
Model 11A Gooseneck Microphone or a
line-level audio signal.