DAC1 USB
Instruction Manual Revision D
Page 14
output drivers, will increase power
consumption, and may cause distortion.
Unbalanced RCA Analog
Outputs
The Left and Right unbalanced outputs use
standard RCA style jacks. The
ground connections are bonded
to chassis ground at the
location where analog ground is
bonded to the chassis. This
minimizes the effects of ground
loops caused by AC currents in
the cable shield.
The RCA output levels may be controlled from
the front panel, or may be set to fixed levels
using the rear-panel
Calibration Trimmers
.
In
Calibrated
mode the RCA outputs are
factory preset to –10 dBV at -20 dBFS. This
is typical for most consumer-grade
equipment.
TIP: Mono summing with an RCA ‘Y’
cable is not recommended as this will
cause high amounts of distortion. Mono
summing with a ‘Y’ cable can be
accomplished with the use of a modified
cable by implementing a 1k Ohm series
resistor in each leg of the ‘Y’.
Note:
The XLR pads do not have any effect
on the level of the RCA outputs.
The RCA output impedance is very low (30
Ohms). This makes these outputs well suited
for driving high-capacitance loads and/or
high-capacitance cables.
TIP: The RCA outputs are capable of
driving cables as long as 1360 feet (see
Table 1). But, long un-balanced cables
will generally suffer from hum problems
due to ground loops. We highly
recommend using balanced
interconnects for long runs.
Low-Impedance Passive Pads
The XLR outputs are equipped with low-
impedance passive pads that may be used to
reduce the output levels while preserving the
full dynamic range of the
DAC1 USB
. The
DAC1 USB
ships with the 20 dB pads
enabled.
TIP: When directly driving power
amplifiers and powered speakers, use
‘Variable’ mode and start with the
factory default 20 dB pad setting. If
necessary, change the pads to achieve a
normal listening level when the ‘Volume
Control’ is near mid-rotation.
When the output pads are enabled, the
output impedance changes slightly, and the
maximum allowable cable length should be
reduced as shown in Table 1 (assuming 32
pF/foot and a maximum allowable loss of 0.1
dB at 20 kHz).
Table 1 - Cable Drive Capability
Balanced Output Drive Capability:
Attenuator
Output
Maximum Loss in dB
Setting (dB) Impedance Cable (ft) at 20 kHz
0
60
680
0.1
10
425
96
0.1
20
135
302
0.1
30
43
949
0.1
Unbalanced Output Drive Capability:
Output
Maximum Loss in dB
Impedance Cable (ft) at 20 kHz
30
1360
0.1
TIP: To set the XLR outputs to typical
professional studio levels, set the pads
to 0 dB, and set the ‘Output Level Switch’
to ‘Calibrated’. If the factory settings of
the ‘Calibration Trimmers’ have not been
changed, the XLR outputs will be
calibrated to +4 dBu at -20 dBFS, and the
RCA outputs will be calibrated to -10 dBV
at -16 dBFS.
