Unbalanced Rca Analog Outputs; Low-Impedance Passive Pads - Benchmark DAC1 PRE Instruction Manual

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 internal 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.
DAC1 PRE Instruction Manual Rev J

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 PRE. The
DAC1 PRE 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 the 12 o'clock position.
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
Setting (dB) Impedance Cable (ft)
0
10
20
30
Unbalanced Output Drive Capability:
Output
Impedance Cable (ft)
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.
Maximum Loss in dB
at 20 kHz
60 680
425 96
135 302
43 949
Maximum Loss in dB
at 20 kHz
30 1360
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