Studio Technologies 55 1996 - Manual (Page 29)

Model 55/56 User Guide Issue 3, December 1996
Studio Technologies, Inc. Page 29
are possible using the latest sophisticated
cable. Test to ensure that the Studio-
Comm system works correctly with the
desired cable length. There are too many
variables to give a simple formula—good
luck!
¼-Inch Plugs versus EIA RS-453
An incompatibility problem lurks between
some ¼-inch 2-conductor and 3-conductor
phone plugs and the jacks found on pro-
fessional audio equipment. While all the
plugs seem to “look” the same, some do
not comply with the industry standard,
called EIA RS-453. This standard defines
the physical dimensions, including the
shape of the plug’s tip. It seems that some
plug manufacturers don’t bother to make
the tip comply with the standard. Why is
this relevant to you? Because the phone
jacks used on the Model 55 Central
Controller, Model 35 Talent Amplifier, and
Model 38 Talent Amplifier do comply with
the standard. They expect to be mated
with plugs that also meet the specification.
When interfacing your line inputs, line
outputs, or headphones be careful with
the plugs you utilize. Should a connection
appear “flaky,” sound noisy, or make an
intermittent contact, the most likely
problem is a non-standard phone plug.
Replace the plug if this is the case. You
should find that all plugs from Switchcraft
or Neutrik will work correctly, specifically
Switchcraft No. 297 or Neurtik NP3C. In
our experience, headphones are the most
likely place to find non-standard plugs—
we even found them on some “world-
class” headphones that we use in our lab!
Definition of Level—dBu and dBV
Whenever possible, 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 0dBm is 1
milliwatt dissipated in the known load (i.e.,
0dBm across 600 ohms will measure
0.775V). In contemporary situations an
output is rarely terminated with 600 ohms;
generally 10k ohms or higher. The dBu
designation is better because it refers to
dB referenced to 0.775V, with no refer-
ence to load impedance. This takes into
account today’s audio scene where sig-
nals have
a low source impedance, and a high input
impedance. The dBu designation is be-
coming the standard for the professional
audio industry.
StudioComm equipment is designed to
interface with audio signals that have
nominal signal levels of –10dBV and
+4dBu. You might wonder why dBV
came into the picture. Most people don’t
realize that equipment that utilizes “–10”
levels usually mean –10dBV—substan-
tially different from –10dBu (–10dBV =
–7.78dBu). The dBV designation is simply
a different way of measuring signal level
and is often used when dealing with por-
table or consumer audio equipment. The
dBV designation refers to dB referenced
to 1.0V, rather than dBu which refers to
0.775V.
“Hot” Disconnection of the Model 56
Control Console
Should you need to relocate the Model 56
while your StudioComm system is operat-
ing, there is no reason why you can’t
disconnect the 5-conductor cable, move
the unit, and then connect it again. If
the Model 56 is disconnected while it is