Studio Technologies ISS - Manual (Page 17)

Issue 3, June 1990 ISS User Guide
Page 18 Studio Technologies, Inc.
ISS
Transformer Coupling
As discussed in the Installation section of
this manual, there may be cases where
transformer isolation of the ISS audio input
and/or output signals may be required. As
the ISS has excellent electronically 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 suggest using transformers
from Jensen Transformers Inc., website:
www.jensentransformers.com. They make
excellent parts and we recommend their
JE-11-DMCF, a 600 to 600 ohm output type
transformer. This should give very good
results on both the input and output sides
of the ISS. If you want to splurge and go
for the premium transformer, you could
use their JE-11-BMCF; overkill but terrific
specs! Because of Jensen’s high quality,
load resistors do not have to be used.
Resistor Loading
Some broadcast operations as standard
practice load the outputs of audio equip-
ment. This is not really necessary with the
design of contemporary audio equipment.
Current practice call for low source imped-
ances and high input impedances; the ISS
follows this practice. Provision has been
made on the I/O Card for load resistors to
be added if required; resistor location R88
for the left input, R64 for the right input.
Carefully insert and solder your selected
resistors. Use diagonal cutters to clip the
excess resistor lead. Do not install load
resistors on the input connectors—only
install them on the I/O Card. This ensures
that double loading will not occur in cases
where the Transfer Relay Assembly connects
the inputs directly to the outputs.
Output Load vs. Output Level
The I/O Card is user selectable for three
nominal operating levels. The input operat-
ing levels are measured in dBu and do not
have to take into account whether the inputs
are terminated (loaded) or not. The outputs
are a different matter. The output stage,
although excellent, is not completely “stiff,”
and will allow the nominal output level to
change slightly with different output load
impedances. The 0, +4, and +8dBu output
levels are stated under the assumption that
a 600 ohm termination will be present. The
nominal output level will change up to
0.5dB with a lower or higher load imped-
ance, e.g. 150 or 20k ohms. This is to be
expected and should pose no operational
problem. Only a “perfect” line output stage
(if it can be found) will maintain an exactly
constant output level with a widely varying
load. This variance with load is constant
with frequency and does not effect fre-
quency response linearity.
Signal Paths
All signals from the outside world come in
and go out via connectors on the Transfer
Relay Assembly. The Transfer Relay As-
sembly links with the mainframe via screw
terminal strips on the mainframe back
panel. The mainframe links with the cards
via 15-position card edge connectors.
Power (+15 and +24Vdc), signal ground,
and earth ground also come into each card
via the edge connectors. All inter-card
connections are made via a 20-conductor
ribbon cable bus. The ribbon cable bus
serves as the audio and logic signal high-
way between the cards. Cross talk is not a
problem as the signal level, type, and
physical positions were carefully chosen.