Altec 781a 1781at pre amplifier

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- ALTEC

1 781 A/AT
Mic/Line Input Module

DESCRIPTION

The ALTEC LANSING 1781A programmable input
module accepts either mic or line level signals through
a wide variety of connector interfaces. Standard features
include an electronically balanced input stage with ad-
justable gain, continuously variable high and low pass
filters, RFI protection, 48 volt phantom powering, two
levels of muting, and remote control capability.
Programming is accomplished with plug-in jumpers
which may select phantom power (on or off) and mute
priority or slave. Optionally available is the ALTEC
LANSING 1785A input isolation transformer which
provides an additional 10 dB of gain for improved
sensitivity. ALTEC LANSING also offers the 1781AT,
a programmable input module with a 1785A
transformer installed.

The 1781A/AT is designed for use with the Altec
Lansing 1700C Mixer/Preamplifier, and 1707C/
1715C Mixer/Amplifiers. Four different input connec-
tors are available: the 1791 Female XLR, 1792 Male
XLR, 1793 Dual Phono, and 1794 5-Lug Terminal
Connector.

KEY SPECIFICATIONS

Gain: 0 dB to 50 dB,
continuously variable.
10 dB to 60 dB w/1785A.
Input Sensitivity:

(Ref. 1 kHz, 0 dBr = 100 mVrms output, 10 kohm load)

Without 1785A: 0.3 mVrms to 100 mVrms
(-50 dBr to 0 dBr).
0.1 mVrms to 30 mVrms
{-60 dBr or -10 dBr).
Input Impedance: (Ref. 1 kHz)

Electronically balanced: 8 kohm.

Transformer balanced: 600 ohm.

With 1793 installed: 39 kohm.

With I7B5A:

Frequency Response:
(Ref. 1 kHz, 100 mVrms output, 10 kohm load)
Without 1785A:
:1 dB (Minimum gain): 20 Hz to 20 kHz.
:1 dB (Maximum gain): 50 Hz to 20 kHz.
With 1785A:
:1 dB (Minimum gain): 20 Hz to 20 kHz.
:t:l dB (Maximum gain): 50 Hz to 15 kHz.

Total Harmonic Distortion (THD):
(Ref. 1 kHz, 100 mVrms output, minimum gain, 10 kohm
load, 30 kHz low pass filter)

20 Hz to 20 kHz: <0.05%.

Equivalent Input Noise: <-120 dBr.
(Ref. 0 dBr = 100 mVrms output, 10 kohm load, 200 ohm
input termination maximum gain, A-weighted)

High Pass Filter (low Cut):

(Ref., 100 mVrms output, minimum gain, 10 kohm load)
Fl: 320 Hz (>10 dB at 100 Hz).
Slope: 6 db/oct (20 db/dec).

Low Pass Filter (High Cut):
(Ref. 100 mVrms output, minimum gain, 10 kohm load)

Fh: 5 kHz (>6 dB at 10 kHz).
Slope: 6 dB/oct (20 dB/dec).
Attenuation:
(Ref. 1 kHz, 100 mVrms output, 10 kohm load)
Mute: >60 dB.

10 kohm remote

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1785A SPECIFICATIONS BLOCK DIAGRAM
Voltage Gain: 10 dB. 1785A MER
OPTIONAL TRANSFOR
Impedance Ratio: 600 ohm : 10 kohm. RED W0" LOW men
(Primary: Secondary) PEER PETER
J1
Frequency Response: N 1 -1-GREEN-o-|:|-o--lwm EA?
(Ref. 1 kHz, 100 mVrms output) 31': 3 FB -
:1 dB: 50 HZ to 15 kHZ. REMOTE 4 o-EI-c { 6
GND 5 F82
Total Harmonic Distortion (TIID): GAIN -10. we
(Ref. 1 kHz, 100 mVrms output)° Ifi em
50 Hz to 20 kHz: <0.2 6.
J2 -18VDC
Insertion Loss: <1 dB. 2:: 1 .l |_. 38%?
(Ref. 1 kHz, 100 mVrms output) GND 2 MlxouT
3
MUTE
Included Accessories: 2 VV - d 0 ho 7 $3.33
2 - Mounting screws. /d7 PHANTOM WW5" POWER

1- Flat washer.

EDGE CONNECTOR

ARCHITECT'S and ENGINEER'S SPECIFICATIONS

The input preamplifier modules shall have
phantom power capability, continuously variable
high and low pass filters, adjustable gain, and L +
R stereo summing. A second model shall also feature
a 600 ohm input transformer. In addition, the
modules shall be fully compatible with the 1700-
series mixer/preamplifier and mixer/amplifier main»
frames, and accept any one of the 1790-series
input connectors.

The input preamplifier modules shall meet the
following performance criteria: Gain: 50 dB (60 dB
w/1785A Input Transformer), continuously variable.

ALTEC

Frequency Response: 50 Hz to 20 kHz, :1 dB.
Equivalent Input Noise: <120 dB below rated output
voltage with a 200 ohm input termination. Total
Harmonic Distortion (TI-ID): <0.05%, 20 Hz to
20 kHz (1781A) or <0.2%. 50 Hz to 15 kHz
(1781AT) at minimum gain. High Pass Filter
Corner Frequency: 320 Hz. Low Pass Filter
Corner Frequency: 5 kHz. High and Low Pass
Filter Slope: 6 dB per octave.

The input preamplifier shall be the Altec Lansing
model 1781A or 1781AT.

a MAFiK IV company

PO. BOX 26105 O OKLAHOMA CITY, OK 73126-0105 0 U.S.A. O (405) 324-5311 or FAX: (405) 324-8981
© 1994 ALTEC LANSING CORPORATION

PRINTED IN U.S.A. 8/94

Revision 1

42-07-027705