Analog Inputs; The Analog Front End; Grounding; Balanced Vs Unbalanced Inputs - Apogee AD-8000 Operating Manual

AES and S/PDIF Input
Connectors: Female XLR connector (AES), RCA connector (S/PDIF)—each carries two channels
Function: Multiplexed AES or S/PDIF receiver
S/PDIF Output
Connector: RCA connector—carries two channels
Function: S/PDIF transmitter
Word Clock/Video In
Connector: BNC connector
Function: Word clock sync in or Video (PAL, NTSC, Mono) in
Word Clock Out
Connector: BNC connector
Function: Word clock sync out
Analog Expansion Card
Connectors: Plug-in edge connector on 0.1" centers on motherboard
Card size: 2in x 6 in approx.
Function: Stereo 24-bit balanced analog output, controlled by headphone amp
selector switch, or 8-channel 24-bit DAC
AMBus Card Cage
Connectors: 120-pin PCI connectors (4)
Card size: Approx 6.3 in deep x 4.5 in wide, height can be one or two slots
Function: AMBus digital I/O cards—a range of cards are available for different functions and interfaces
Connection: To AMBus
The Analog Front-End
The analog front-end contains common-mode and differential filters, +4 dBu (default)/–10 dBV gain switch-
ing, a balanced gain stage with 20 dB of gain, a precision balancing circuit (for unbalanced inputs), buffer ampli-
fiers to drive the A/D, and Apogee's proprietary Soft Limit circuit with trimpot-adjustable thresholds.
To adjust the Soft Limit threshold, it is necessary to remove the unit's top cover. See the Card
Installation and Adjustments Guide at the end of this manual.

Grounding

Analog shield grounds are normally tied only to chassis ground. A jumper on each channel, near the
XLR connector, can be shorted to connect the shield to analog ground. This is potentially useful for an
ungrounded analog source, although it is not recommended under normal conditions. To change the
jumper settings, it is necessary to remove the unit's top cover. See the Card Installation and Adjustments
Guide at the end of this manual.

Balanced vs Unbalanced Inputs

The AD-8000 can accept unbalanced or balanced inputs. Unbalanced inputs are dynamically balanced
before being applied to the A/D inputs.
For optimum performance, use balanced inputs whenever possible.
Headroom and Gain Adjustment
The attenuator is designed as a compromise between keeping the signal as "hot" as possible, in order to
maintain a high S/N ratio, and attenuating the potentially very high peak signal levels of professional line levels
(up to 28 dBu) so that up to 20 dB of headroom adjustment is available in the first stage.
AD-8000 Operating Manual

Analog Inputs

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