Jensen
Twin
Servo 990 Mic Preamp:
Transformer
enhanced technology for superior sonic performance.
Bringing science to
sound.
The
Jensen Twin Servo 990 Mic Preamp is considered the
world's finest mic
preamp by audio experts. It's the ideal integration of
advanced design
software, hardware, engineering know-how, and carefully
controlled
'golden ears' tests. It has earned high marks for sonic
performance
since its introduction in 1988.
The
basic circuit was originally published as an application
note by Jensen
Transformers for their finest microphone input
transformer, the
JT-16-B. Each channel uses two
precision 990C
operational amplifier modules, developed and patented by
Deane Jensen,
to achieve one tenth the distortion and twice the
bandwidth of a single
stage design.
The Jensen
Twin Servo 990
mic preamp has a 19" wide
mainframe rack-mount chassis (1.75"H x 19"W x 8"D) and
can be ordered
with 1 to 4 channels. Additional channels can be easily
added later up
to the total capacity of the mainframe.
Highlights:
•
JT-16-B Input Transformer. Jensen's best mic input
model.
•
Two
990 Discrete Op-Amps Per Channel. Faster, quieter, more
powerful and
better sounding than typical monolithic op-amps.
•
Elimination Of All Coupling Capacitors From The Signal
Path. Results in
less degradation of the audio signal.
•
JT-11-BMQ Output Transformer. Jensen's best line output
transformer.
•
Input Bias Current Compensation Circuitry And DC Servo
Circuitry.
Eliminates signal degrading coupling capacitors.
Standard
Features:
•
Fully Sealed Conductive Plastic Gain Control. Provides
smooth
continuous gain adjustments from 16dB to 60dB.
•
20
OHM MIC switch or 20dB PAD switch.
•
POLARITY REVERSE switch.
•
PHANTOM POWER switch.
•
All
Front Panel Switches Are LED Illuminated.
•
Gold Plated XLR Connectors for maximum reliability.
•
Ground Lift Switch On Each Channel. Helpful for
eliminating ground
loops.
•
VU-1 meter. Very accurate and informative 20 segment LED
meter, with
separate Peak LED, for monitoring preamp output.
•
Toroidal Power Transformer With Additional Shielding.
Eliminates hum
problems so no external power supply is needed.
•
Universal Power Supply. Internal switch provides six
primary voltage
choices to accommodate use anywhere in the world.
•
Chassis Ground Isolation Switch. Helpful for eliminating
ground loops.
•
Pin
2 Or Pin 3 High. Internal jumpers make changes in the
field easy.
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Jensen Twin Servo 990
Standard Channel Detail |
|
|
Jensen Twin Servo 990
Back Panel Detail |
Specifications,
typical
(0dBu = 0.775V):
Voltage Gain Range |
+1dB |
16 to 60 |
dB |
|
|
|
|
E.I.N.,
20-20kHz
bandwidth, unweighted, 60dB gain, 0dBu
=
0.775V |
150 Ohm source |
-128.7 |
dBu |
|
|
|
|
Frequency Response,
ref: 1kHz |
20Hz |
-0.05 typ, -0.1 max |
dB |
|
20kHz |
-0.05
typ, -0.1 max |
dB |
|
0.4Hz
and 140kHz |
-3 |
dB |
|
|
|
|
Time
Domain Response |
|
|
|
Deviation
From Linear Phase (maximum) |
20Hz to
20kHz |
+2 |
deg |
Group
Delay |
20Hz to
120kHz |
2.16 +0.05
|
µs |
Squarewave
Risetime |
|
2.2 |
µs |
Squarewave
Tilt |
20Hz |
5.8 |
% |
|
|
|
|
Total
Harmonic
Distortion (note 1) |
|
|
|
Output
Level +4dBu, any gain setting |
100Hz to
20kHz |
0.001
typ, 0.003 max |
% |
|
20Hz |
0.036
typ, 0.100 max |
% |
Input
Level +8dBu (note 2) |
100Hz to 20kHz |
0.001
typ, 0.003 max |
% |
|
20Hz |
0.120
typ, 0.300 max |
% |
|
|
|
|
Common Mode Rejection
Ratio |
60Hz |
125 |
dB |
|
1kHz |
100 |
dB |
|
10kHz |
80 |
dB |
|
|
|
|
Common Mode Input
Voltage |
|
+300 |
V-pk |
|
|
|
|
Optimum microphone
Impedance (switch selectable) |
|
150/20 |
Ohms |
|
|
|
|
Input
Impedance, +15%
max |
20Hz to 20kHz |
1.27 |
k Ohms |
|
|
|
|
Phantom
Power |
|
|
|
Voltage |
|
+52 |
VDC |
Current
(maximum) |
|
9.5 |
mA |
|
|
|
|
Maximum
Output Level |
75 Ohm load |
+24 |
dBu |
|
|
|
|
Output
Load Impedance
Range |
minimum/nominal |
150/600 |
Ohms |
|
|
|
|
Output Source Impedance |
20Hz to
20kHz |
70 +5
|
Ohms |
|
|
|
|
Power
Requirements, 4
Channels |
+15% |
100,
120, 140, 200, 220,
240 |
VAC |
|
|
48 to 66 |
Hz |
|
|
25 |
Watts |
|
|
|
|
Dimensions
(note 3) |
|
1.75H x
19W x 8D |
Inches |
|
|
|
|
Notes
: |
|
|
|
Unless
otherwise specified : 25°C ambient, 150 ohm
source, 600 ohm load. |
(1)
Low frequency response distortion is almost
entirely 3rd harmonic. |
(2)
Worst case of maximum possible input at minimum
gain with unclipped
output. |
(3)
Handles extend 1" beyond the front panel. |
"Twin
Servo" is a registered trademark of Jensen
Transformers,
Inc. |
|