Studio Technologies 80 M80-00273, User Manual

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Issue 4, March 1997 Model 80 User Guide
Page 14 Studio Technologies, Inc.
To confirm that a signal is present on the
input of the Model 80 you can plug the
headphones into the loop-through con-
nectors associated with the left and right
channels. After ensuring that the level will
not hurt your ears, you can listen for the
presence of audio and get an idea of the
general quality of the source. With a bal-
anced input signal you should hear the
input in both the left and right earpieces
of the headphones. With an unbalanced
source you would, in most cases, hear
signal in only the left channel of the
’phones.
To confirm that signals are present on the
eight stereo outputs you can plug the
headphones into the left and right output
jacks. Outputs configured for +4dBu
operation will be significantly “louder” in
the headphones. Since all Model 80 out-
puts are balanced, you should observe
signal in both the left and right earpieces.
Rapidly “walking through” the 16 output
jacks will confirm the proper operation of
the Model 80.
Technical Notes
¼-Inch Plugs versus EIA RS-453
An incompatibility problem lurks between
some ¼-inch 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 indus-
try 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 80 do comply with the standard.
They expect to be mated with plugs that
also meet the specification. When interfac-
ing with the Model 80 be careful with the
plugs you utilize. Should a connection
appear “flaky,” sound noisy, or make an
intermittent contact, the most likely prob-
lem is a nonstandard 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 Neutrik NP3C.
Definition of Level—dBu
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 0.7747V).
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 0.7747V, with no reference to load
impedance. This takes into account
today’s audio scene where signals have a
low source impedance, and a high input
impedance. The dBu designation is be-
coming the standard for the professional
audio industry.
–10 Output Level Reference
To those of you who are technical
“nitpickers” we feel than an explanation
is in order. Operational simplicity, rather
than historical convention, led Studio
Technologies’ to make the –10 outputs
referenced to dBu rather than to dBV. We
are well aware that in the past a “–10”
output was often referenced to 1 volt, not
to 0.7747. When the Model 80 was first
designed it was assumed that the “+4