Studio Technologies 750 - Manual (Page 36)

Issue 3, May 1997 Model 750 User Guide
Page 36 Studio Technologies, Inc.
Model 750
Don’t misunderstand our position: Ex-
tended dynamic range is great for music
recordings. We love listening to terrific
classical, jazz, and, when available, pop
recordings. But for the applications served
by the Model 750 dynamic range is not
really a factor. Go ahead, prove us wrong
and use the Model 750 to record the
London Symphony Orchestra. Then you
should turn the limiter/compressors off!
Technical Notes
¼-Inch Plugs and EIA RS-453
An incompatibility problem lurks between
some ¼-inch 2-conductor and 3-conduc-
tor phone plugs and the jacks found on
professional 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 750 do
comply with the standard, and they expect
to be mated with plugs that do, too.
Should a connection seem “flaky,” sound
noisy, or make intermittent contact, the
most likely problem is a nonstandard
phone plug. Replace the plug if this is the
case.
You should find that all plugs from Switch-
craft or Neutrik will work correctly, specifi-
cally Switchcraft No. 297 or Neutrik NP3C.
In our experience, headphones are the
most likely place to find nonstandard
plugs—we even found them on some
“world-class” headphones that we use
in our lab!
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 outputs were terminated with 600
ohm loads. In this way it was easy to say
that “0dB” was 1 milliwatt dissipated in the
known load (i.e., 0dBm across 600 ohms
will measure 0.775V). Today, 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 load impedance not a
factor. This takes into account the contem-
porary audio scene where most equip-
ment has a low output source impedance,
and a high input impedance.
External Monitor Input 2
This section is buried here because we
are almost certain that no one in manage-
ment will ever read this far into the guide!
Sources connected to the external monitor
inputs will usually have a nominal level of
+4dBu, so why the –10/+4 DIP switch for
input 2? Frankly, we thought that field
engineers may sometimes want to con-
nect a piece of –10 “consumer” audio
gear for their own “personal monitoring.”
While operating a remote vehicle can be
challenging and fast-paced, it can often be
filled with hours of waiting. The ability to
connect a compact disk player or cassette
“Walkman” may make the time pass a little
more pleasantly!
You might recognize that we selected
–10dBu, even though the –10 designation
usually implies –10dBV. We feel that
–10dBu is a better sensitivity when con-
necting to “–10” equipment. As –10dBV =
–7.78dBu, the extra 2.22dB of sensitivity is
helpful.