Studio Technologies 2A 2015 - Manual (Page 17)

Model 2A User Guide Issue 2, March 2015
Studio Technologies, Inc. Page 17
pins pass through the Model 2A’s on/off
control circuitry (the “off hook” relay) from
pins 3 and 4. Refer to Figure 7 for connec-
tion details.
The jack on the Model 2A’s back panel that
is labeled 2 can be used to connect two
different signals: telephone interface 2 input
and telephone interface 2 switched output.
Pins 3 and 4 bring the tip and ring leads
into telephone interface 2. (They are electri-
cally in parallel with pins 5 and 2 on the
jack for interface 1.) Pins 6 and 1 can be
connected to a telephone device which
would receive the signal connected to the
interface 2 input whenever the Model 2A’s
interface 2 circuitry is not active (interface
2 is “on-hook”). The connections on these
pins pass through the Model 2A’s on/off
control circuitry (“off hook” relay) from pins
3 and 4. Pins 2 and 5 are not used and
should be left un-terminated. Refer to
Figure 7 for details.
Signal Levels and Receive Trim Pots
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 while the transmit level is ap-
proximately –6 dBu. A trim pot, accessible
on the front panel, is 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.
Figure 7. Telco jack connection details