Installation manual

2–32 Hardware installation
DMX 3500 Digital to Analog Converter
Analog Meter Output Gain
When a DMX 3500 D to A convertor board is installed, the Analog Left/Right Meter Outputs of the DAP 3500/4000
can be used to drive analog meter circuitry such as a mechanical VU meter or equivalent. (A drawing of the DAP rear
panel is shown on page 2a–5). These meter outputs use a simple consumer quality D to A convertor and are not intended
for monitoring signal quality. They have good frequency response and correct gain, but suffer from more noise and distor-
tion than is acceptable for high quality speaker feeds.
The conversion to analog signal levels provides a further problem: “What voltage level will be represented by this –20
dB full scale signal used in the digital domain?” The DAP provides the following four settings:
1. +8 dBu
2. +4 dBu
3. 0 dBu
4. –3 dBu
These settings are provided by the Audio Meter Gain menu on the Saturn System Control Defaults menu (page 3–38).
The Analog MONA and MONB outputs are intended to drive monitor speaker amplifiers and therefore have a fixed max-
imum level. This will correspond to the 0 dBu setting above. As such when the monitor pots on the control panel are set
at maximum, and a –20 dB full scale signal is present on the digital outputs, the analog MONA and MONB outputs will
be 0 dB u. These outputs use high quality 20 bit convertors with carefully designed anti–imaging filters that provide for
minimum group–delay and phase shift in the audio bandwidth. These analog outputs will compare favorably with those
from high quality outboard audiophile D–to–A convertors. In addition, they benefit from the very low jitter internal
clocks providing maximum signal performance.
Output Level Controls
The DMX 3500 has trimmer pots on each analog output. These are designed to compensate for small gain variations in
the circuitry as well as to compensate for different loading conditions. The DMX 3500 is calibrated at the factory for
a high impedance load. The DMX 3500 can drive any load impedance from infinite to 600 ohms. Due to the approximate-
ly 66 ohm output impedance of the output drivers used for MONA and MONB, a 600 ohm load will cause approximately
a 0.93 dB level drop. Adjusting the output trimming pots can correct for this level loss. The analog meter outputs have
approximately a 50 ohm impedance and therefore will have a smaller loss of approximately 0.75 dB. Adjusting the output
trimmers can also compensate for this level loss.