Studio Technologies IFB Plus 2005 - Manual (Page 20)

Issue 8, December 2005 Model 2 User Guide
Page 20 Studio Technologies, Inc.
Bring an audio source into the auxiliary au-
dio input and test the VOX interrupt feature.
Set the VOX input switch to the middle posi-
tion, connecting the auxiliary audio input to
the VOX circuitry. Use the VOX output switch
to assign the VOX output to one of the IFB
channels. On the channel you selected for
VOX interrupt watch the VOX and IFB status
LEDs light when signal is detected. Use the
monitor amplifier to monitor VOX interrupt
activity.
Try receiving audio via telephone interface 1.
Use the receive audio as a program source.
Use the receive level trim pot to vary the
receive audio level. Use the receive audio
as a source for the VOX interrupt function.
Telephone interface 2 has more features; try
them all. If set for the telephone line mode,
let the interface automatically answer an
incoming telephone call. Use the interface
to receive, as well as send audio. Use the
receive audio as a program source. Use the
receive level trim pot to vary the receive au-
dio level. As with interface 1, use the receive
audio as a source for the VOX interrupt.
Test the Model 22 Access Stations. Is the
interrupt audio loud and clear? Observe the
status lamps inside the pushbutton switch-
es. Do the appropriate lamps light fully
bright when an interrupt takes place?
If an access station is configured to mute
the Model 2’s monitor output, ensure that
the monitor speaker does mute during an
interrupt.
In all cases, you should hear clear, click-free
audio. We intended the Model 2 to sound
great—if not, call us for technical help. A
completed installation should be reliable,
easy to use, and perform to high sonic stan-
dards. Questions and comments from the
field are welcomed and encouraged!
Technical Notes
Schematic Diagrams
Schematic diagrams are available to all pur-
chasers of IFB Plus systems. Contact Studio
Technologies’ support, via phone or email,
to obtain the electronic files. The schemat-
ics show the graphical representation of all
the electronic components, along with their
electrical value and connections. Traditional-
ly, a problem with schematics has been the
decimal point marking. It either disappears
due to bad printing, or dust, dirt or other
imperfections end up looking like decimal
points. For clarity, Studio Technologies has
adopted a more “European” component
marking scheme. Upon first review it may
seem quite confusing, but it can eliminate
problems. For resistors, the designation “K”
for kilo (1000) has been moved to the deci-
mal point position. A 4700 ohm resistor is
shown as 4K7, rather than 4.7K. An example
for a one percent value, a 49900 ohm resis-
tor would be shown as 49K9. For capacitors,
the letter “r” is simply substituted for the
decimal point marking. A 0.47uf capacitor is
shown as r47uf. Once you are accustomed
to this system you may well prefer it.
Definition of Level
Studio Technologies has opted to use the
dBu designation as it seems to be quite
rational. Using dBm was fine when all audio
line outputs were terminated with 600 ohm
loads. In this way it was easy to say that 0
dBm is 1 milliwatt dissipated in the known
load (i.e., 0 dBm across 600 ohms will mea-
sure 0.775 V). In current situations an output
is rarely terminated in 600 ohms; generally
5 k ohms or higher. The dBu designation is
better because it refers to dB referenced to
0.775 V, with no reference to load imped-
ance. This takes into account the current