Studio Technologies Gen II - Manual (Page 8)

Issue 3, July 1991 Generation II User Guide
Page 10 Studio Technologies, Inc.
Technical Notes
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
0dBm is 1 milliwatt dissipated in the known
load (i.e., 0dBm across 600 ohms will mea-
sure 0.7746V). In contemporary situations,
an audio output line is rarely terminated in
600 ohms; generally it’s 20k ohms or
higher. The dBu designation is a better
reference because it refers to dB refer-
enced to 0.7746V, with no reference to load
impedance. This takes into account today’s
audio scene with load impedances varying
greatly. When the Generation II’s specifica-
tions refer to the maximum output level in
dBu, this would translate to dBm only when
the output is terminated with 600 ohms.
Transformer Coupling
As discussed in the Installation section of
this manual, there may be cases where
transformer isolation of the Generation II’s
line input and/or output signals may be
required. As the unit has excellent electroni-
cally balanced input and output circuitry,
interfacing with most other equipment
should not require transformer isolation
except in the strangest of cases. If you do
find a case where you need them, we sug-
gest using transformers from Jensen Trans-
formers Incorporated, 10735 Burbank Blvd.,
North Hollywood, CA 91601, telephone
(213) 876-0059. They make excellent parts
and we recommend their JE-11-DMCF, a
600 ohm to 600 ohm output type trans-
former. This should give very good results
on both the input and output sides.
Resistor Loading
Some audio and broadcast operations
maintain as standard practice termination
resistors on all audio lines. This is usually
done at the input stage of all pieces of audio
equipment. This is not necessary with the
design of most contemporary audio equip-
ment. Current practice calls for low source
impedances and high input impedances.
The Generation II follows this practice. A
problem can occur if you choose to load the
line input and output signals connected to
the Generation II. Double loading can occur
if you have wired the Generation II via a
patch bay and you patch around the unit.
The output of the device driving the Gen-
eration II will now be driving the two line
inputs of the device connected to the out-
puts of the Generation II. This double load-
ing may reduce the audio level being sent to
the next piece of audio equipment. The best
solution is to load neither one. In fact, load-
ing the Generation II’s line outputs does
nothing to improve performance. It basically
just wastes output current. Be aware of this
situation if you decide to use load resistors.
Non-standard Input and Output Levels
Studio Technologies designed the Genera-
tion II to match the audio operating levels of
most facilities. If you are the creative type
who likes to experiment, or the unlucky one
who inherited a facility and has an operating
level different from 0, +4, or +8dBu (ref.
0.7746V), don’t despair. The 0, +4, or +8
settings are used to optimize the Genera-
tion II’s performance, and using a slightly
different operating level will make only
minor differences in performance. If you are