| 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.
 |
| 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" and "Comtran" are registered trademarks of Jensen Transformers,
Inc. |
|