Handbook

Table Of Contents
Redbox User Handbook No 3
35
6 RB-DMA2 Dual Digital Microphone Amplier
Introduction
Fig 6-1: RB-DMA2 Front Panel.
The RB-DMA2 consists of two independent low-noise microphone pre-
ampliers for converting microphone level signals to digital AES/EBU,
or S/PDIF, and analogue line level outputs. The RB-DMA2 can be used
as a front end for digital mixing desks or routers, which do not have
microphone inputs. The analogue outputs can be used for routing to
talkback systems.
The microphone inputs are XLR-3 type and are electronically balanced. The input gain for
each input can be adjusted individually by coarse and ne gain controls on the front panel
and each input has a level indicator. Additionally the ne gain control knob can be disabled
by internal jumpers. A switch on the rear panel allows input 1 to be routed to both left and
right digital outputs, or as input 1 to left output and input 2 to right output respectively.
For each channel there are independent switches to control a high pass lter (low frequency
roll-o at 125Hz) and to provide phantom power at +48V to the connected microphones.
It also has AES/EBU, S/PDIF and Word Clock sync inputs.
The unit operates in four modes:
Master Mode - In this mode the unit receives a microphone-input signal, which is digitised
and formatted for digital serial transmission (IEC958). The necessary clock signals are
generated internally from an on board master clock at a selectable rate (32kHz, 44.1kHz,
48kHz, 64kHz, 88.2kHz or 96kHz).
Slave Mode - In this mode the unit automatically detects the presence of a digital audio
sync signal, if present at the digital input or word clock input, and synchronises the digital
output to it. If no sync is present, no output will be generated.
Auto Mode - Here the unit synchronises to the digital audio sync signal if present at the
digital input and uses the internal master clock only if no sync input signal is detected. In
this case, the internal master clock is used at the selected sample rate.
Auto Lock Mode - This operates like the auto mode except that if no sync-input signal
is detected, it will use the internal master clock to sync to the sample rate which was last
clocked to. When operating in sync modes, the front panel power LED ashes whenever the
unit is not synchronised to the incoming digital signal, or when the unit is being calibrated.
The unit should be calibrated once it has been powered up for more than 10 minutes.
6
MICROP HONE AMPLIF IERS
& LIMITERS
MICROPHONE AMPLIFIERS & LIMITERS - RB-DMA2