Studio Technologies ISS - Manual (Page 7)

Issue 3, June 1990 ISS User Guide
Page 8 Studio Technologies, Inc.
ISS
and RF pickup rejection, shielded cable
must be used for the audio signals. Studio
Technologies uses the convention of pin 2
high, in honor of the European microphone
makers! In most cases, it is correct to
connect the shield lead to pin 1 of the XL
connectors. Pin 1 on the audio input and
output connectors are common with the ISS
Mainframe power supply ground, chassis
ground, and power cord ground leads.
Maintaining consistent left and right audio
input and output polarity is very important
for correct performance of the ISS.
If possible, use patch points on the input
and output signals of the ISS. Installation,
testing, and servicing procedures will be
greatly improved if the ISS is easily placed
on and off line. Make sure that the ISS can
be “patched around” while allowing test
signals to be sent to and returned from
the ISS.
The ISS audio input signals generally arrive
from the master control switcher, an STL,
leased telephone lines, etc. All audio pro-
cessing (limiting, compressing, etc.) should
be performed prior to the audio getting to
the ISS. This helps to ensure that the ISS
simulated stereo remains mono compatible.
The source should be balanced and line
level. If the audio equipment contains audio
output transformers, load resistors match-
ing the source impedance may need to be
inserted and soldered into the I/O card. In
many cases the value of the resistors would
be 600 ohms. Loading of the output trans-
formers can prevent “ringing” of the audio
signals. The quality of the output transform-
ers is the determining factor when deciding
whether to load or not to load. Bad trans-
formers tend to need loading; good ones
generally do not. Refer to the Technical
Notes section of this manual for more
information on installing load resistors.
The ISS audio output signals usually go
directly to the transmitter, or to the transmit-
ter via an STL or leased lines. The ISS
audio outputs are low impedance, electroni-
cally balanced, line level, direct coupled.
They are capable of driving virtually all line
inputs (low or high impedance, transformer
or transformerless). The ISS can even drive
150 ohm loads at high signal levels, not
bad huh!
The ISS uses electronically balanced input
and output circuitry. Best performance is
achieved if the equipment sending signal
to, and receiving signal from the ISS is
operating in a balanced mode. The ISS
input and output stages will operate cor-
rectly in an unbalanced mode, but selected
performance characteristics will be sacri-
ficed. On the input side you will lose the
ability to reject common-mode signals that
balanced operation affords. On the output
side you will lose 6dB maximum output
level. This is not a technical fault but is
inherent in electronically balanced output
stages. If unbalanced input operation is
required, strap pin 3 to pin 1 on the male
connector that will mate with the ISS. Con-
nect the unbalanced input signal high lead
to pin 2, and signal ground to pin 1. If
unbalanced output operation is required,
strap pin 3 to pin 1 on the female connector
that will mate with the ISS. Connect the
unbalanced output signal high lead to pin 2,
and signal ground to pin 1.
In most cases, transformer coupling be-
tween audio equipment is neither required,
nor desirable. If the equipment sending
signal to, or receiving signal from the
ISS requires the isolation given by a