Teletronix® LA-2A Leveler Collection Manual

The ultimate collection of the most revered optical compressor ever

With its gentle, program dependent optical compression, and meticulously designed tube amplifier, the LA-2A is the go-to compressor for professional mixers around the world. In 2001, Universal Audio set the standard in analog emulation with the original UAD LA-2A plug-in.

Today, UA's engineers have redesigned the LA-2A plug-in with more obsessive detail. The Teletronix LA-2A Leveler Collection for UADx features immaculate models of three highly sought-after LA-2A units, giving you the most authentic emulations ever of this iconic compressor.

  • Track and mix with three historic versions of revered Teletronix LA-2A Leveling Amplifiers, each with its own distinctive sonic attributes
  • Record through a Teletronix LA-2A/LA-2 in real time with Apollo interface
  • Dial-in ideal optical compression textures for vocals, bass, drums, and more
  • Harness presets from LA-2A users Ross Hogarth, Darrell Thorp, and Vance Powell

The Teletronix® Story

Teletronix founder Jim Lawrence first used photocells for controlling audio gain in the early 1960s. His ingenious optical compression design was a technological breakthrough, far surpassing the stability and transparency of earlier circuits. Universal Audio founder M.T. "Bill" Putnam later purchased this patented technology, continuing to manufacture the LA-2A for years to come.

Three Historical Units

The Teletronix LA-2A Leveler Collection puts three of the most coveted incarnations of the iconic Teletronix processor at your fingertips. Like the hardware, the LA-2A Silver, LA-2A Gray, and LA-2 models offer distinct variations in time constants, compression knee, headroom, distortion, program and frequency dependence, and more.


Teletronix LA-2A Silver interface


Teletronix LA-2A Gray interface


Teletronix LA-2 interface



LA-2A Plug-In Family

The complete LA-2A family consists of three individual plug-ins. Each variation has its own unique sonic characteristics.

The state-of-the-art algorithms in the Teletronix LA-2A Leveler Collection take full advantage of modern CPU resources and the design sophistication and expertise gained since the introduction of the original LA-2A plug-in in 2001.

Teletronix LA-2A Silver

With a brushed aluminum panel and original T4B gain reduction module, this cherished late-1960s "Silver" version of the LA-2A, manufactured by Bill Putnam, is perhaps the most flexible of the three plug-ins in the collection. Its fast time constant makes it suitable for the widest variety of program material, including transient-rich sources like drums and percussion.

Teletronix LA-2A Gray

Jim Lawrence's original mid-1960s "Gray" version the LA-2A maintains a more average time constant, providing a range of "medium-speed" compression.

Teletronix LA-2

The exceptionally rare, early 1960s LA-2 unit preceded the LA-2A by several years. It provides the slowest response and a unique "mellowed" sound due to 50 years of luminescent panel aging inside the T4 module. Use the LA-2 with legato tempos and vocal sources for a transparency and sublime mood unlike any other compressor.



Operational Overview


In the 60s and 70s, the LA-2A and 1176 became inextricably linked as the must-have dynamic tools of the day. If the 1176 is to the Stratocaster in terms of immediacy and flexibility, then the LA-2A is to the Gibson Les Paul in terms of warmth and one-of-a-kind, magical sonic distinction. An important characteristic of the T4 photocell response is that it is both program and frequency dependent. The T4 cell has a multi-stage release, and can take a few minutes to fully recover from the incoming signal.

The primary use is as individual inserts for sources that require nominal transparent gain reduction, such as vocals, bass, strings or horns. These tools can also be used to isolate the "color" of the output amplifier by turning off the Peak Reduction control, even to extreme distortion settings. An interesting sidechain distortion can be achieved at the most extreme Peak Reduction settings, which primarily affects low frequencies.


No compressor is as easy to operate or instantly satisfying to use as the Teletronix Levelers. Peak Reduction applies the compression threshold to the incoming signal up to -40 dB, while Gain amplifies the signal for level matching post Peak Reduction. Set the metering view on any of the units with either +4 or +10 dB Output Gain, or Gain Reduction. Both LA-2A Gray and Silver expose the hardware's rear Limit/Compress switch, as well as the unit's "R37 FM Broadcast Emphasis" filter as front panel parameters. Although not present on the unit originally, the LA-2 was "hot-rodded" to include Emphasis, which is exposed on the front panel. Lastly, Power bypasses all processor use, providing a handy level matching tool not found on the original hardware.

Artist Presets

The Teletronix LA-2A Leveler Collection includes artist presets from prominent LA-2A users. The artist presets are in the internal factory bank and are accessed via the preset manager. 

Reference Level

Plug-ins in the Teletronix LA-2A Leveler Collection operate at an internal reference level of -12 dBFS. This enables more range in the primary controls (Peak Reduction and Gain) before the I/O distortion characteristics become apparent (signals at the input of these plug-ins can be pushed higher before they distort). 



LA-2A Controls

Each model in the LA-2A plug-in collection has the same control set, except for the added Mix control on the LA-2. The parameter descriptions below apply to all models unless otherwise noted.

Peak Reduction

This control sets the amount of signal compression by adjusting the trigger threshold. Increasing the value lowers the threshold, and therefore increases the amount of compression. The available range is 0 dB (fully counter-clockwise) to -40 dB (fully clockwise).

Note: The front panel knob values, which range from 0-100, are arbitrary and do not reflect any particular dB value.

Rotate this control clockwise until the desired amount of compression is achieved. To monitor the amount of Peak Reduction, set the VU Meter knob to Gain Reduction. Peak Reduction should be adjusted independently of the Gain control.

When Peak Reduction is set to its minimum value, no compression (or limiting) occurs but the signal is still colored by the circuitry and the output level can be adjusted with the Gain control.


The Gain knob increases the output level by up to 40 dB to compensate for the reduced level that results from compression. Adjust the Gain control after the desired amount of compression is achieved with the Peak Reduction control. The Gain control does not affect the amount of compression.

Note: The front panel knob values, which range from 0-100, are arbitrary and do not reflect any particular dB value.

Meter Knob

This rotary knob sets the mode of the VU Meter. When set to Gain Reduction, the VU Meter indicates the Gain Reduction level in dB. When set to +10 or +4, the VU Meter indicates the output level in dB (when set to +4, a meter reading of 0 corresponds to an output level of +4 dB).

VU Meter

This is a standard VU meter that displays either the amount of gain reduction, or output level, depending upon the setting of the Meter Function switch.

On/Power Switch

Determines whether the plug-in is active. When the Power switch is in the Off position, the plug-in is disabled and UAD DSP usage is reduced (unless UAD-2 DSP LoadLock
is enabled).


This switch sets the compression ratio of the leveler. When set to Compress, the compression ratio is approximately 3:1 and when set to Limit, the ratio is approximately infinity:1. However, the compression ratios are nonlinear and frequency dependent, so these figures are not absolute.

Note: Like the original hardware, this control is unavailable on the Teletronix LA-2 plug-in. The plug-in is "hardwired" in Limit mode.


A blended output balance between the signal processed by the plug-in and the original dry source signal can be adjusted with the Mix "set screw" control. Mix facilitates parallel compression techniques without having to create additional routings in the DAW.

Note: The Mix control does not exist on the original hardware.

When Mix is set to 0% (fully counter-clockwise), only the unprocessed dry source signal is output. When set to 100% (fully clockwise, the default value), only the processed wet signal is output. When set to 50% (12 O’Clock noon position), an equal blend of both the dry and wet signals is output. The balance is continuously variable, and phase accurate, throughout the control range.

Tip: Click the "+" or "-" text labels to increment or decrement the current value in tenths. 


The (R37) Emphasis "set screw" knob controls a shelf filter circuit in the compressor's sidechain input, thereby enabling frequency-dependent compression.

When the control is fully clockwise (the default position), the sidechain signal is unfiltered and all frequencies in the source signal that exceed the compression threshold will trigger gain reduction equally (within the non-linear constraints of the electro-optical characteristics).

Rotating the Emphasis control counter-clockwise increases filtering of the sidechain signal. The Emphasis filter gradually reduces the lower frequency content of the sidechain signal, resulting in compression that is less sensitive to those frequencies, and more sensitive to high frequency content. Therefore, as the sidechain filtering is increased, higher frequencies are compressed more.

Side-Chain Pre-Emphasis (R37) Background

The LA-2A hardware was designed for use in broadcast applications. The audio signal in FM broadcasting undergoes pre-emphasis and results in a 17 dB boost at 15 kHz. Due to this increase in signal level, transmitters are subject to over-modulation. The LA-2A hardware provides a control (R37) which controls the amount of high-frequency compression.

This potentiometer is factory set for a "flat" side-chain response (clockwise). Increasing the resistance of this potentiometer by turning it counter-clockwise will result in compression which is increasingly more sensitive to the higher frequencies.



Historical Background

In the 1950s while at Parsons Electronics, Electrical Engineer Jim Lawrence was quietly asked to join the Titan Missile Program based at Cal Tech's Jet Propulsion Lab and was assigned to develop optical sensors for the program. Fortunately for everyone, the technology developed from Lawrence's work lead back to a more peaceful deployment of the optical sensor, as the detector in his future Leveling Amplifier. The interactions of the luminescent panel with the photo resistors in his T4 design are predominantly what gives the Teletronix Levelers their signature sound.

Lawrence later broke out on his own to start Teletronix, setting up shop in his hometown of Pasadena, California in 1958. Among the Teletronix line of products were transmitter tubes, multiplex generators, to full-scale radio transmitters. Jim's first pass at his Leveling Amplifier was realized as the Teletronix LA-1; Around 100 units were made. Lawrence then updated the design to the LA-2 with improved specs and circuit layout, then moved quickly to the industry standard LA-2A. In 1965, just three years after the incarnation of the LA-2A, Jim Lawrence sold the company to Babcock Electronics. Enter Bill Putnam. Putnam picked up Babcock's broadcast division including Teletronix, and rolled it into his parent company, Studio Electronics in 1967. From there, Universal Audio resumed manufacturing of the LA-2A, and Putnam began using the optical detector for new designs.

Whether serendipity or by intent, Jim Lawrence's Teletronix Levelers and his T4 design had the right musical response that allowed the LA-2A the sonic and technological longevity it still retains. Universal Audio spent a long time getting the T4 right for their hardware LA-2A reissue and the plug-in. But what was special about it wasn't fully understood until UA began the research to model the LA-2A for the UAD-1. Modern photocells are designed to be as fast as possible, but they don't have the right multi-stage response they need to sound like a Teletronix design. Our DSP research helped us understand how the original T4 worked at the quantum physics level. This not only allowed us to develop an accurate DSP model of the gain reduction behavior, it also helped us make our hardware T4 more consistent. This involved studying the original photocell formula, working with both modern device physicists and the people who developed the original photocells, locating the special equipment originally used to manufacture these back in the ‘60s, and re-qualifying the manufacturer. Whether hardware or DSP, it is this special qualified manufacturing process and "recipe" UA re-established that gives the LA-2A its unique, musical sonic quality to this day.LA-2A-HW.png

The Teletronix LA-2A Leveler Collection original hardware units

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