— —
8
channels. Since these are “bridging” (high impedance) inputs, they
provide no termination for the console or other equipment which feeds
the
DAVID-II
. Please feel at liberty to connect a 600-ohm resistor
across the input terminals should you feel this really necessary. Most
professional equipment nowadays features low output impedances and
high input impedances. The concept of 600-ohm “line-matching” dates
from the age of transformer coupling and is rooted in the mystique of
telephone practices. More often than not, audio line impedance
matching is poo-pooed by today’s hip broadcasters (you) and
equipment manufacturers (us).
Unbalanced
Inputs
In rare instances the
DAVID-II
may be fed from “semi-pro” gear with
unbalanced outputs. “Disco” mixers fall into this category and are
perfectly serviceable for installations on a tight budget. In such cases,
the single center conductor of the shielded input lead should be
connected to the + terminal, and the shield to
G
.
In addition,
a
jumper wire should be installed between the – terminal and
G
.
Input Gain
Range
The
DAVID-II
can accommodate line-level program inputs with a
nominal “Zero-VU” value between –15dBu and +15dBu. This 30dB
range is divided into two 15dB ranges by internal jumpering.
As shipped, the
DAVID-II
is jumpered for professional level inputs
between 0dBu and +15dBu. Most console and STL receiver outputs
fall into this range, +4dBu, +6dBu and +8dBu being typical levels.
Lower levels, between –15dBu and 0dBu, may be encountered when
interfacing with “semi-pro” gear or with feeds via lossy studio-
transmitter telephone line circuits. The extra gain for the low level
range is enabled by changing jumpers beneath the top cover.
Gain Jumpers
Under the top cover, and just behind the
PROGRAM LINE INPUT
barrier strip, you will find two jumper pin strips, each with a “push-
on” jumper. The strips are identified as
JMP3
and
JMP5
in the circuit
board legend, and each has an
H
and an
L
marking to indicate the
proper jumper placement for High level and for Low level inputs,
respectively. Figure 2 illustrates jumpering options.
HIGH LEVEL INPUTS
(0dBu to +15dBu)
LOW LEVEL INPUTS
(–15dBu to 0dBu)
Figure 2 -
PROGRAM LINE INPUT Range Selection
