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Remote controlled 8 channel analog mic preamp - 3 separate outputs per channel: analog + digital; includes control software
Features:
Size - The Model 1788
contains eight preamps in 2RU space. Since there is a fair amount of
heat dissipation, there should be at least 1RU spacing between every
preamp. In that configuration, they may be stacked to provide 40
channels of high quality preamps in a standard 16RU road case.
Microphone Output Limiter -
All preamps have a maximum input level. Once that level is exceeded,
there is no way to remove that very unpleasant distortion. In order to
avoid that occurrence, many engineers set the preamp so that the
expected peak level at maximum sound level is still at least 12dB below
the clip point. While this provides some insurance against the preamp
clipping, it causes a loss of noise performance and, in the case of
digital, a loss of resolution. The Model 1788 has a unique limiter
(patent pending) in the front end of the preamp which limits the output
level of the microphone by as much as 20dB, hence the name 'Microphone
Output Limiter'. This allows the engineer to get maximum noise
performance and also allows maximum resolution for an analog to digital
converter, all without worrying about crashing the preamp.
26dB Pad - The Model 1788
has 39dB of adjustable input gain and fixed gain of 26dB for a total
maximum gain of 65dB. There is a 26dB pad which will allow a preamp to
be run as a unity gain buffer stage. For example, this allows the line
level output of a wireless mic receiver to be fed into the preamp.
Adjustable Maximum Output Level
- The maximum output level of the Model 1788 is +24dBm (loaded into 600
Ohms) balanced. There are, however, many input stages which have odd
maximum input levels (e.g.-+18dBu). In order to retain the function of
the microphone limiter and maximize noise performance of the entire
audio system, the Model 1788 has output level trim of up to 24dB. Once
the maximum input level of the device following the Model 1788 is
defined, the output level of the 1788 can be trimmed to that exact
level. The input gain of the 1788 is then adjusted to achieve optimum
performance. In addition to the 24db of output adjustment, each output
may be muted.
Separate Analog Outputs -
Microphones are often passively split and then fed to two or more
locations. The Model 1788 has two separately trimmable, buffered analog
outputs. The main output on XLR is transformerless servo-balanced and
the second output is tranformerless balanced on a DB25 multipin
connector. This allows two separate inputs to be fed at optimal levels
from an optimized mic preamp.
Digital Option - In addition
to the analog outputs, the Model 1788 has three optional digital
outputs. The analog to digital converters are 24 bit with selectable
sampling rates. The sampling rates can be generated from an internal
clock or an external source. The Model 1788 employs a drift stabilized
A/D converter circuit (patent pending) which eliminates DC from the
output without incorporating a digital high pass filter. The digital
outputs appear on two DB25 connectors, one for AES/EBU and one for the
T/DIF format. There is also a TOSLINK optical output for the ADAT
format. There is an AES/EBU input on an XLR and a Word Clock on a BNC
connector for external clock input. If the unit is being used as a
master there is an AES/EBU output on an XLR. For even more flexibility
with complex setups, see Aphex's Model 148 DIGITAL SPLITTER.
Test Tone Generator - There is a 700Hz test tone at two different levels which can be bussed to any selected preamp channel. The two levels are at 0dBfs (maximum output level) and -20dBfs. The test tone at 0dBfs allows easy set up for finding maximum peak input into following stages. The -20dBfs tone is useful for digital systems which use a -20dB reference tone for '0Vu'.
Display - The Model 1788 has LED indicators for the status of each function for each channel. A twelve segment LED meter displays headroom. Two eight segment LED's show input gain or maximum output level on either of the two analog outputs. All indicators and metering can be monitored at the remote location.
Headphone Output - As an additional feature, the Model 1788 has a front panel headphone output. Any channel can be selected and the output level adjusted.
Also available: 1788-1 Digital Output Module for 1788A - AES / EBU, TDIF™, and ADAT™. Simultaneous optical outputs - 8 channel - 24bit/44.1, 48, 96kHz (AES only).
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