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1788A
Remote Controlled Mic Preamp System |
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| The
Model 1788A Microphone Preamp and Model 1788RC Remote Controller
form a complete Microphone preamp system with 5 outputs (3 digital
and 2 analog) available simultaneously |
| The
Problem ! |
| Long
mic level lines, mic splitters, and multiple inputs reduce
the sensitivity of the microphone and change its frequency,
phase, and transient response. This performance degradation
is the result of shifts in impedance, capacitance, and inductance
values and is quite audible.
Phantom power on a mic line causes the line itself to become
a microphone. Jiggling the line will create audible effects.
Having the phantom power source as close as possible to the
microphone also reduces the chance of phantom voltage loss
within a very long cable run.
Most
modern preamplifiers have excellent common mode rejection
ratio, often approaching 110dB. If there is common mode signal
(noise) built up in cable run and the gain of the preamp is
60dB, the residual common mode noise is only 50dB down. While
common mode signal can be present in a short line as well
as a long line, there is a higher probability that there will
be more common mode signal in the longer line, especially
if that line is crossing power and lighting cables and a high
RF field. |
| Applications |
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By
placing the 1788A close to the mics and controlling it remotely
the need for long mic level runs is eliminated. |
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The
noise picked up by long cable runs is no longer boosted at the
end of the lines since the preamp gain has already been taken
at the input of the line. |
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By
providing 5 outputs ( 3 Digital and 2 Analog ) that are usable
simultaneously, the need for splitter boxes is essentially eliminated,
although if you DO need additional digital splitting, check
out our Model 148 Digital Audio Splitter. |
| Why
Remote Control? |
1788RC
Remote Controller |
| Almost
all live applications require the monitoring of mic preamp gain.
If there isn't an engineer sitting next to the preamps on stage,
there must be a way to control them from a remote position.
All
parameters of the 1788A are remotely or locally controllable,
and setups, snapshots, and recall of presets are quickly and
easily available.
The
remote control protocol for the 1788A is Ethernet. 8 banks,
16 units, or 1024 Channels can be remotely controlled.
There
are three ways to control the 1788A remotely: |
1. |
Via
the 1788RC - Hardware Remote Controller |
2. |
Via
PC or Mac running the 1788SW controller software (Win 95/98/2000/XP®
or Mac OS X® compatible)
The control software has a screen which displays all parameters
and metering of one unit at a time and up to 16 units may be
called up. All channel status information and metering are displayed
in real time. A channel can be selected and settings modified.
Scenes can be saved, modified and recalled in the control software.
The software also contains a 'learn' function in which the channel(s)
adjust the preamp gain to a definable peak value based on the
input level during the 'learn' time. (A representative screen
from the software is shown below.) |
3. |
Via any device that generates MIDI, such as a MIDI controller,
mixer, sequencer, or show control system |
Screen Capture showing 1788SW software |
| Features |
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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. |
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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. |
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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. |
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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. |
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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. |
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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 our
Model 148 DIGITAL SPLITTER. |
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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'.
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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. |
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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. |
Shown
above is a typical setup for the 1788A in a Live Sound Application
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| Aphex
Proprietary Technologies |
| MicLim™
is a patented limiter circuit at the mic input - a mic level
limiter that speeds setup and makes the 1788 virtually crash-proof.
MicLim allows you to set for maximum noise performance without
having to back off for headroom, and eliminates the need for
constant gain riding...plus fiber or digital systems can be
driven at levels that yield maximum resolution without fear
of overload.
LeNA™,
the digitally controlled Low Noise Amplifier, allows the 1788's
input gain to be adjusted without noise or glitches. This
patented Aphex circuit changes level in 1/4 dB steps with
1dB stops. Other remote controlled preamps use relay switching
with step sizes as high as 10dB. Even a step size of 1/4dB
without LeNA will cause an audible click or pop that at high
gains could be explosive! |
| Audio
Quality |
The
1788A provides 8 balanced Jensen® transformer-coupled microphone
preamplifier inputs which offer audiophile sound quality
far in excess of the mic preamps found in most mixing consoles.
It also provides two separately trimmable analog outputs
for each channel. The optional digital output module allows
simultaneous output of 24 bit AES/EBU, T/DIF® and ADAT®
Optical.
These
A/D converters are selectable up to 96 kHz and are Aphex
proprietary "Drift Stabilized" (patented) which eliminate
the need for high pass filtering in the digital domain.
Because the inputs to the A/D converters are trimmed exactly
to the outputs of the preamp, digital resolution can be
maximized without fear of crashing. This makes the 1788
the perfect front end to any DAW, fiber system, or digital
console.
|
1788A Rear Panel Shown
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1788RC Remote
Controller panel shown
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Specifications
- Aphex 1788A
Remote
Controlled Microphone Preamplifier System |
| RANGE SETTING: |
0dB |
-10dB |
| Audio |
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Frequency
Response |
±0.5
dB 10Hz to 50 kHz |
same |
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Nominal
Gain |
0dB
+14dB / -21dB |
0dB
+8dB / -21dB |
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Signal/Noise
(Ref +4dBm) |
-84dB |
-94dB |
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THD
(Ref 1kHz, no limiting) |
<0.006%
(+12dBu in) |
<0.006%
(+2dBu in) |
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SMPTE
IMD |
<0.006% |
<0.006% |
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Max
Input (MIL) |
+26dBu |
+16dBu |
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Max
Output Level (MOL)* |
+24dBm
Peak |
+14dBm
Peak |
| *(MOL is limite
,.d by the peak ceiling setting. The output stage
is capable of +25dBu into 600 ohms) |
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Crosstalk |
-60dB
up to 10kHz |
same |
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Dynamic
Range |
104
dB |
same |
| Inputs and
Outputs |
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Input
Circuits |
Servo
Balanced Transformerless |
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Output
Circuits |
Servo
Balanced Transformerless |
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Input
Connectors |
3-pin
XLR Female |
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Output
Connectors |
3-pin
XLR Male |
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Input
Impedance |
19.5k
ohms unterminated; 600 ohms by rear panel switch
(terminator lifts in bypass mode) |
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Output
Impedance |
65
Ohms |
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Input
CMRR |
Better
than 50dB 20Hz to 20kHz |
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Input
RF Rejection |
Better
than 40dB at 800kHz; better than 60dB above 2 MHz |
| Controls
and Adjustments |
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Input
Gain |
+14dB
/ -21dB |
+8dB
/ -21dB |
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LF
EQ |
±5dB |
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LF
Crossover |
100Hz
/ 210Hz |
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HF
EQ |
±5dB |
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HF
Crossover |
1.7kHz
/ 3.4kHz |
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Release
Time |
150msec
to 7 seconds |
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Density |
-5
to +5 RCH |
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Output
Ceiling |
-9
to +24dB (peak) (=peak value of sinewave) |
| Other Specifications
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Power
Requirements |
120
VAC 50-60 Hz 30 Watts (100, 220,
240 options) |
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Power
Fuse |
100/120
VAC = .375A SloBlo; 220/240 VAC = .25A SloBlo |
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Dimensions |
19"W
x 1.75"H x 9.5" D (482.6mm x 44.5mm x 241.2mm) |
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Net
Weight |
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There
are no downlaods available for this product at the moment.
But please contact
us
should you require further information.
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