Studio Technologies 50 2000 - Manual (Page 32)

Issue 4, July 2000 Model 50/51 User Guide
Page 32 Studio Technologies, Inc.
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.
Intermittent Audio Connections
Should you experience audio connections
that seem to be “flaky” or intermittent,
refer to the Technical Notes section of this
guide. The ¼-inch 3-conductor phone
jacks used on the StudioComm products
are of very high quality, conforming to the
industry standard EIA RS-453. Some
plugs do not meet this standard, specifi-
cally in the shape of the tip conductor. In
rare cases you may have to replace plugs
on interconnecting cables or headphones
to remedy an interconnection problem.
Switchcraft No. 297 or Neutrik NP3C
phone plugs will function correctly.
Clicks in the Audio
As covered in the Configuration section
of the manual, the seven stereo line inputs
can be configured for –10dBV or +4dBu
operation. Setting an input for –10dBV,
while connecting an audio source with a
+4dBu nominal level will lead to distortion
(“clipping”) of the signal. In this fault
condition the user would hear a harsh
“clicking” 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 +4dBu operation.
The distortion 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 connect-
ing Model 35 or Model 38 Talent Amplifi-
ers to the Model 50 Central Controller. The
maximum cable length is directly related
to the amount of resistance in the connect-
ing 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 or Model 38 needs to see
at least +20Vdc between pins 1 and 2 of
their input connector. The Model 50’s
talent amplifier output voltage across pins
1 and 2 is +23Vdc, with a maximum
current draw of 0.2A (200mA). This differ-
ence between the voltage supplied and
the voltage required results in a maximum
voltage drop of 3V over the interconnect-
ing 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 volt-
age drop by the maximum current flow: 3V
divided by 0.2A = 15 ohms. For example,
a standard 20 AWG microphone cable is
Belden 8412, which has 10.9 ohms resis-
tance per conductor per 1000 feet. Since
we’re using two conductors to carry the
signal (pins 1 and 2) you’d get 21.8 ohms
per 1000 feet of microphone cable. With
our 15 ohm maximum resistance you’d be
able to use 688 feet (210m) of this cable.