Universal Audio 1176LN User manual

Model 1176LN
Solid-State Limiting Amplifier
Universal Audio, Inc.
www.uaudio.com
PO Box 3818
Santa Cruz CA 95063-3818

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Universal Audio 1176LN
Thank you for purchasing this reproduction of the classic 1176LN compressor. When my
father designed this product, he was very proud of his accomplishment. Being a recording
engineer himself, this was a piece of gear he used extensively. He was also very proud of
its reception by his peers in both the recording and broadcast industries.
In making our version of this classic piece of equipment, we have taken great care to make
a product that my father would have been proud of. Throughout the development of this
product our philosophy has remained clear: Stay true to the original. There are good
reasons why certain pieces of gear have become classics, and we wanted to make sure
that we captured this accurately.
You may be familiar with the fact that there were many versions of the 1176 produced
throughout the years. We patterned our reproduction on the D/E versions. These versions
were characterized by the transformer input stage, LN circuitry, and the class A (1108
style) output stage. Later versions replaced the class-A output stage with a push-pull class-
AB output stage, and eventually replaced the transformer input with a differential op-amp
circuit. That highly recognizable blackface 1176 sound was best captured by the version
that we are reproducing.
As for the future of Universal Audio, we are making more reproductions of classic
recording equipment beyond the 1176LN and the Teletronix LA2A. We are interested in
your opinions about your favorite vintage pieces, what you like or didn't like, what you'd
love to own but can't find any longer, etc. Additionally, Universal Audio will produce new
quality audio products designed to meet the needs of the modern recording studio yet
retain the character of classic vintage equipment.
Developing these products has truly been a special experience, enjoyed by all who have
been involved. While it is on the surface a business endeavor, it's really been so much
more than that - equal parts a sentimental and technical adventure. More than anything,
we have been surprised and touched by the overwhelming response and warm support
that we have received since we announced the return of Universal Audio. We thank you,
and we thank my father, Bill Putnam.
Sincerely,
Bill Putnam

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1176LN

User’s Guide
Universal Audio, Inc.
PO Box 3818
Santa Cruz, CA 95063-3818
[phone] voice
[phone] fax
www.uaudio.com
Universal Audio Part Number 1176-M01.
Revision 1.02
Notice
This manual provides general information, preparation for use, installation and operating instructions for the
Universal Audio 1176LN, Limiting Amplifier.
The information contained in this manual is subject to change without notice. Universal Audio, Inc. makes no
warranties of any kind with regard to this manual, including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose. Universal Audio, Inc. shall not be liable for errors
contained herein or direct, indirect, special, incidental, or consequential damages in connection with the
furnishing, performance, or use of this material.
Copyright
2000 Universal Audio, Inc. All rights reserved.
This manual and any associated software, artwork, product designs, and design concepts are subject to
copyright protection. No part of this document may be reproduced, in any form, without prior written
permission of Universal Audio, Inc.
Trademarks
1176, LA-2A, and the Universal Audio, Inc. logo are trademarks of Universal Audio, Inc. Other company
and product names mentioned herein are trademarks of their respective companies.

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UNIVERSAL AUDIO 1176LN .................................................................................II
1176LN SPECIFICATIONS..............................................................................................................................1
INSTALLATION...............................................................................................................................................2
Rear Panel Connections...............................................................................................................................2
230 Volt Operation.....................................................................................................................................2
Stereo Interconnection.................................................................................................................................2
1176 LN OPERATION...................................................................................................................................3
Meter Function / On-Off Pushbutton Switches............................................................................................3
Compression Ratio.......................................................................................................................................3
Input Level.....................................................................................................................................................3
Output Level.................................................................................................................................................3
Attack Control...............................................................................................................................................3
Release Control............................................................................................................................................4
Stereo Operation.........................................................................................................................................4
CALIBRATION ................................................................................................................................................5
“Q” Bias........................................................................................................................................................5
Meter Driver Null.........................................................................................................................................5
Zero Set........................................................................................................................................................5
Stereo Interconnection.................................................................................................................................5
THEORY OF OPERATION .................................................................................................................................7
Overview ......................................................................................................................................................7
1176 LN Input Section.................................................................................................................................8
Gain Reduction Stage..................................................................................................................................8
LN Circuitry...................................................................................................................................................9
Output Amplifier...........................................................................................................................................9
Gain Reduction Control Circuit..................................................................................................................10
HISTORY.....................................................................................................................................................12

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1176LN Specifications
!Input Impedance: 600 Ω, bridged-T control (floating)
!Output Load Impedance: 600 Ω(floating)
!External Connections: XLR Connectors / Original Jones barrier strip
!Frequency Response: +/- 1 dB. 20Hz to 20 kHz
!Gain: 45 dB, +/- 1dB
!Distortion: Less than 0.5% T.H.D. from 50 Hz to 15 kHz
with limiting, at 1.1 seconds release setting.
Output of +22 dBm with no greater than 0.5%
T.H.D.
!Signal-Noise Ratio: Greater than 81 dB with input signal at
threshold of limiting, over a bandwidth of 30 Hz
to 18 kHz
!Attack Time: Adjustable from 20 to 800 microseconds.
!Release Time: Adjustable from 50 milliseconds to 1.1 seconds.
!Stereo Interconnection: Using 1176 SA stereo interconnect accessory
!Power Requirements: 110V / 220V operation
!Dimensions: 3.5” vertical, for mounting in standard 19” rack.
!Weight: 11 lbs. (Shipping weight 14.5 lbs.)

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Installation
Rear Panel Connections
Both XLR style connectors as well as the original terminal strip are provided for both input
and output connections. Additionally, as in the original unit, terminals are provided for
the connection of a remote meter. When using a remote meter, remove the strap on the
barrier strip and connect the leads to a standard VU meter.
230 Volt Operation
The 1176LN can be configured for either 115 or 230 Volt operation. This is selected by
the voltage selection switch on the rear panel.
Stereo Interconnection
Two 1176 LN units can be linked for stereo mode operation using the 1176 SA stereo
adapter. See the ‘Calibration’ chapter for instructions on calibrating the 1176 SA.

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1176 LN Operation
Meter Function / On-Off Pushbutton Switches
The pushbutton switches located to the right of the meter are used to determine the
metering mode as well as to turn the unit on and off. The 1176LN is turned on by
selecting any pushbutton other than the Off selection.
The VU meter can be used to indicate either Gain Reduction or output level. When used to
measure output level, the user can choose either +4 or +8 dBm output. The Meter function
is determined using the four pushbuttons to the right of the meter. When GR is depressed,
the meter reads Gain Reduction level in dB. When the +4 or +8 buttons are depressed,
the meter displays the limiter output level. When +4 is depressed, a meter reading of 0
corresponds to an output level of +4 dBm.
Compression Ratio
The four pushbutton switches to the left of the meter control the compression ratio. Four
ratios are provided: 20:1, 12:1, 8:1, and 4:1. The 20:1 and 12:1 settings are typically
used when peak-limiting is desired, while the 4:1 and 8:1 settings are used for general
dynamic range compression.
Input Level
The 1176LN uses a fixed threshold level, and utilizes the Input Level control to determine
the relative threshold as well as the total amount of gain reduction.
In order to set the limiter to provide a specific amount of compression, first adjust the Input
and Output controls to a fully counterclockwise (CCW) position. Adjust the Attack control
a few degree clockwise (CW) so that Gain Reduction is enabled. Use the Meter
pushbutton switches so that the meter reads Gain Reduction. Rotate the Input Level control
CW until the desired amount of gain reduction is achieved.
Output Level
Once the desired amount of limiting is adjusted by setting the Input Control, the Output
Control can be used to set the required output level.
Set the meter to measure the output level by pressing either +4 or +8. Adjust the Output
Control until the desired output level is achieved.
Attack Control
The Attack Control adjusts the time it takes the limiter to respond to an input signal and
adjust the gain appropriately. Additionally, when it is in the fully CCW position,

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compression is disabled. The Attack Control potentiometer allows for an adjustable
response time of 20-800 microseconds. The fastest attack time is achieved when the
Attack Control is in its fully CW position.
Release Control
The Release Control allows for an adjustable release time of 50 to 1100 milliseconds. The
fastest release time is achieved when the control is in the fully CW position.
Stereo Operation
When used in stereo operation, the Attack and Release controls on the two units will
interact. Controlling the Attack and Release on either of the units controls both units.
When connected in a stereo configuration, the fastest attack time is double that of a single
unit.

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Calibration
Note: There are no user serviceable parts inside the
Universal Audio 1176LN. Unit calibration as well as repair
should only be performed only by qualified service
personnel. These calibration procedures are provided only
for use by qualified service technicians.
“Q” Bias
The compression threshold is set using R59. Under normal circumstances, this control does
not need to be adjusted. The threshold is dependent upon the specific characteristics of
the VVR FET (Q1), and it will be necessary to re-adjust it if Q1 is changed.
The following procedure is used to set “Q” bias:
!Select either +4 or +8 output metering
!Adjust R59 fully counterclockwise (CCW)
!Apply a sine wave signal to the limiter
!Use the Input and Output Controls for 0dB output
!Slowly adjust R59 CW until the output decreases 1.0 dB
Meter Driver Null
A multimeter is needed to perform this calibration procedure.
!Disconnect any input and output connection on the 1176LN
!Set multimeter to measure dc volts
!Depress the Meter GR pushbutton
!Adjust “0” set potentiometer, R71 (located on the front panel) so that the meter
reads near 0 dB
!Connect the multimeter across R74
!Adjust R75 for a minimum voltage reading
!Disconnect the multimeter
!Readjust “0” set potentiometer, R71 so that the meter reads 0 dB
Zero Set
R71, located on the front panel is used to zero the meter. Adjust this potentiometer if the
meter needs to be recalibrated.
Stereo Interconnection
Using the 1176SA, two units may be connected for stereo operation. Use the following

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procedure to calibrate the 1176 stereo adapter:
!Remove the signals from both 1176 units
!Disable the gain reduction on each limiter (rotate both ATTACK controls fully
CCW)
!Connect the 1176-SA to both limiters (This requires two RCA style cables.)
!Use the METER function pushbutton switches to set both units into GR mode
!Adjust the potentiometer on the 1176-SA until both meters read 0dB
!If it is not possible to zero both meters, reverse the stereo interconnect cables and
repeat the preceding step