Model 1176LN Solid-State Limiting Amplifier Universal Audio, Inc. www.uaudio.
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.
User’s Guide 1176LN Universal Audio, Inc. PO Box 3818 Santa Cruz, CA 95063-3818 (831) 454-0630 voice (831) 454-0689 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.
UNIVERSAL AUDIO 1176LN ................................................................................. II 1176LN SPECIFICATIONS ..............................................................................................................................1 INSTALLATION ...............................................................................................................................................2 Rear Panel Connections .........................................................................
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.
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.
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.
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.
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.
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.
Theory of Operation Signal Input Signal Output Input Pre-Amp GR Circuit Output Amp GR Control Circuit Figure 1 - Block Diagram of the 1176LN. Overview Figure 1 shows the block diagram of the 1176LN Limiting Amplifier. Signal limiting and compression is performed by the Gain Reduction section. Before the signal is applied to the Gain Reduction section, the audio signal is attenuated by the Input stage. The amount of attenuation is controlled by the input control potentiometer.
Figure 2 – 1176 Input Section 1176 LN Input Section The 1176LN Input Section is comprised of an adjustable passive attenuator followed by a transformer. The purpose of this section is to reduce the signal level so as not to overdrive the FET based gain reduction stage. Additionally, the adjustable input level is used to control the amount of compression. This input circuit was used in Revisions A-F. With Revision G, a differential op-amp input instead of the attenuator / transformer input stage was used.
will result in a higher voltage from the Gain Control Circuit, which will lower the gain, hence reducing the signal level. This is the basis of the limiting action. Note that the 1176 is a feedback style compressor since the sidechain circuit samples the signal level after the gain reduction. Signal In Signal Out R5 27k Signal In R5 27k Signal Out Q1 GR Control Voltage Figure 4 - Using a FET as a voltage-variable resistor.
To GR Circuit From Pre-Amp output R21 56k, 1/4w 4:1 S1A R20 56k,1/4w 8:1 S2A R19 68k, 1/4w 12:1 S3A 20:1 R75 470,1/4w R6 1k 4:1 S4A U2 + R38 47k Q8 2N3707 50uf C20 50V R47 47k R54 470 Q9 2N3707 R42 180k 2N3707 R48 7.68k R40 2.4k C19 Q10 2N3707 6.8uf, 35V + R49 2.4k CR2 U3 Release Time Control R55 25k R52 47k R43 38.3k R56 5M C21 + R39 4.7k R64 1.5k S4B C27 .022 U3 R37 470k 20:1 Attack Time Control (F.P.) R46 1k Q7 S3B R76 150 S1 C17 1uF R68 1.
by regulating how fast C22 is charged. Likewise, R56 determines the compressors release time by controlling the rate at which C22 discharges. The output of this stage is then applied to the gate of the FET in the Gain Reduction circuit which in turn controls the gain in the manner previously described.
History It was Bill Putnam himself who, in 1966, was responsible for the initial design of the 1176. Its circuit was rooted in the 1108 preamplifier which was also designed by Putnam. As is evident from entries and schematics in his design notebook, he experimented with the recently developed Field Effect Transistor (F.E.T.) in various configurations to control the gain reduction in the circuit. He began using F.E.T.
“The 1176 absolutely adds a bright character to a sound, and you can set the attack so it's got a nice bite to it. I usually use them on four to one, with quite a lot of gain reduction. I like how variable the attack and release is; there's a sound on the attack and release which I don't think you can get with any other compressor. I listen for how it affects the vocal, and depending on the song I set the attack or release--faster attack if I want a bit more bite.
also known for his work with Red Hot Chili Peppers, Natalie Merchant and Wilco. “I use 1176s real conservatively and they still do amazing things,” he comments. “I'm always on the four to one button, and the Dr. Pepper--you know, 10 o'clock, 2 o'clock, and it does everything I need. “ “I always use them on vocals. I use them on room mics, on acoustic guitars--sometimes in mixing I'll sneak a little on a snare drum or a separated channel of a snare drum.
