8
LINE INPUTS AND RANGE SELECTION
Digital Input
Connection
The rear-panel
AES/EBU DIGITAL I/O INPUT
is a transformer-
coupled XLR female connector that accepts 16/24-bit stereo digital
inputs at sampling rates of 32kHz, 44.1kHz and 48kHz. Sampling
rate selection is automatic, and the rate is displayed on the front-
panel LCD. The digital input also synchronizes the digital line out-
put to the same rate, except when analog inputs are used.
Left and Right
Analog Input
Connections
The
ANALOG LINE INPUT
(s) are rear-panel female XLR connectors.
These are electronically-balanced (transformerless) high impedance
bridging inputs that do not provide termination for the console or
other equipment that feeds the 261. Most professional equipment
nowadays has low output impedances and high input impedances.
The concept and folklore of 600-ohm line matching dates from the
age of transformer coupling and is rooted in ancient telephone prac-
tices. With few exceptions, audio line impedance matching is hap-
pily disregarded by today s hip audio industry.
Unbalanced
Analog Inputs
The Model 261 may be fed from unbalanced outputs, such as found
on disco mixers and consumer entertainment electronics. For un-
balanced lines, the single center conductor of the shielded input lead
should be connected to Pin 2 of the XLR connector, and the shield
connected both to Pin 1 and to Pin 3.
Analog Input
Gain Range
The 261 can accommodate line-level program inputs with a nominal
Zero-VU value anywhere between 25dBu and +10dBu. A set of
jumpers beneath the top cover optimizes the range of the menu-
accessed
INPUT GAIN
adjustment and helps to avoid A/D converter
headroom issues.
As shipped, the Model 261 is jumpered for line levels in the +4dBm,
range, common to most audio consoles and other professional studio
gear.
Higher program levels are typical of early US broadcast practices,
but may still be encountered in European installations. Lower levels
are typical of semi-pro or consumer products, or with feeds from
lossy studio-transmitter telephone line circuits.
Gain Jumpers
Analog input gain-set jumpers are located beneath the top cover and
at the end of the rows of components directly behind the
ANALOG
LINE INPUT
connectors. They are labeled JP1 and JP2 for the
RIGHT
and the
LEFT
channels, respectively. Each jumper strip has a
push-on jumper shunt, which may be placed in 3 positions as
shown in Figure 2 on the following page.
The three push-on positions are marked: 10, 0 and +10. Choose
the position that is closest to the nominal, zero-VU program line
level that is connected to the analog input of the Model 261. If the
line level is +4dBm, select the
position. If interfacing with con-
sumer-equipment line levels, 10 is the proper choice. The dBu
clipping point of the analog input stages and/or A/D converter is ap-
proximately 30dB above the figure shown. The 261 would have ap-
proximately 26dB of analog headroom with a +4dBm program line
