Studio Technologies ISS - Manual (Page 20)

ISS User Guide Issue 3, June 1990
Studio Technologies, Inc. Page 21
ISS
“soft” bypass. The ISS will usually be in
this mode when stereo program material
is present on the left and right audio inputs.
When a Simulate from Left or Simulate from
Right command is given, the ISS mode will
change from Bypass to Sim from Left or
Sim from Right. During normal ISS on-air
operation, the state of the Bypass mode
will be changing in response to mono and
stereo input signals.
ISS Mainframe Grounding
The ISS mainframe contains two ground
circuits: earth and signal. Earth ground is
connected to all metal parts of the chassis,
the ground pin of the AC power connector,
pin 3 on each of the circuit card edge con-
nectors serving the mainframe card slots,
and pin 1 of the four XL-type connectors.
Signal ground is the common point for the
power supplies and is connected to pins 4
and 11 on the mainframe card slots, and to
the relay driver circuitry on the Transfer
Relay Assembly. These grounds, electrically
isolated in the stock mainframe arrange-
ment, are connected together via one point
in the ISS. This point is a jumper wire con-
necting pins 3 and 4 of edge connector P1
on the I/O Card. In most cases, this is the
preferred ground arrangement, insuring
safety and good shielding of the audio
signal wires. In certain cases it may be
desirable to isolate this ground. IN NO
CASE IS IT PERMISSIBLE TO FLOAT THE
CHASSIS FROM EARTH GROUND. This is
a safety ground and must connect via the
third wire of the power cord to an approved
ground. To isolate the signal ground from
the chassis, remove the previously men-
tioned jumper wire. Note this change on
your schematics for later reconnection if
required.
Remote Control Signals
One of the nicest features of the ISS is the
ability to control many functions remotely.
Two types of input signals can be used:
continuous or momentary. Switches on the
I/O Card, Polarity Correction Card, and
Mode Select Card set which type of signal
is to be recognized. We’ll consider a remote
control signal as a logic high whenever
current meeting the ISS specifications is
flowing into a remote control input. When
set for continuous, the remote control input
circuitry is enabled whenever a logic high
is present. When set for momentary, the
remote control input circuitry is leading
edge triggered. The transition from low to
high is considered a valid remote control
signal; a high to low transition is ignored.
Testing the ISS
Proof of performance tests on your broad-
cast facility commonly use sine waves of
different frequencies and levels to check
such things as frequency response, noise,
and distortion. Very unusual results can
occur if ISS performance tests are made
using sine wave or constant frequency
signals. These results are due to the way
the stereo simulator boards perform their
function, taking a mono input and delaying,
randomizing, and gyrating the signal into
a stereo image. Simulating stereo from a
fixed single frequency input will usually
result in different left and right output levels
that will appear to change randomly as the
input frequency is varied slightly. This is
completely normal and expected. Remem-
ber that the usual input signal to the simula-
tor cards is a complex music, voice or other
natural sound. To get rational proof of
performance data, place the ISS in the