LA-2A Leveling Amplifier
The LA-2A was invented by James F. Lawrence II, founder of the Teletronix Engineering Company in Pasadena, California in the early 1960s. The LA-2A had evolved from Lawrence's first leveling amplifier, the LA-1, which was favored by Gene Autry, and its successor, the LA-2, which had been adopted by CBS and RCA. In 1965, Lawrence sold Teletronix to Babcock Electronics of Costa Mesa, California, and in 1967 Bill Putnam's company Studio Electronics (eventually renamed UREI), acquired Babcock's broadcast division, including the Teletronix brand. 
Three versions of the LA-2A were made until 1969.
After Universal Audio was re-established in 1999, the company re-issued an updated version of the LA-2A.
The LA-2A is a hand-wired, tube-based compressor. It uses an electroluminescent panel together with a cadmium-sulfide light-dependent resistor (which in the LA-2A's own terminology is called the T4 cell) to provide gain reduction. The properties of the T4 give the LA-2A its unique character by making it an entirely program-dependent design.
The LA-2A has simple controls: a Peak-Reduction knob controls the gain of the side-chain circuit, and therefore, the gain reduction; a Gain Control for make-up gain; and a Limit/Compress switch which alters the compression ratio. The VU meter may also be switched to show the gain reduction or output level.
The LA-2A has the ability to preserve the impression of performance dynamics while performing extreme level management--a sonic character that makes it sought after by many recording engineers, particularly for use on vocals and bass guitar.
Recording engineers who cite the LA-2A in their work include Joe Barresi, Mike Clink, and Tony Maserati. The LA-2A was used to record Alanis Morissette's vocals on Jagged Little Pill, Kurt Cobain's vocals on Nevermind, and Shakira's vocals on "Hips Don't Lie". Joe Chiccarelli used an LA-2A to add distortion to Jack White's vocals on The White Stripes' album, Icky Thump.
LA-2As warm things up. ...they EQ all the warmth and low mids and bass. When you put bass and drums in them they get fatter and bigger. And unless you hit them way hard and make the tubes sizzle they don't really distort.— Jim Scott
Universal Audio has offered an officially-branded Teletronix LA-2A software plug-in since 2002, when they included the first version with their UAD-1 PCI DSP card. An updated version was introduced in 2013, when UA released the LA-2A Classic Leveler Collection for their UAD-2 platform, which included three different versions of LA-2A: the late-'60s 'Silver' version, the mid-'60s 'Gray' version, and the early-'60s LA-2.
- The LA-3A, a transistorised version of the LA-2A
- The 1176 Peak Limiter, another popular vintage compressor descended from the LA-2A
- Fuston, Lynn. "A History of the Teletronix LA-2A Leveling Amplifier". Universal Audio. Universal Audio.
- "LA-2A Manual" (PDF). Archived from the original (PDF) on 2006-11-13. Retrieved 2009-03-11.
- Cooper, Michael (November 2000). "Universal Audio LA-2A". Mix. Future Plc. Retrieved 10 September 2021.
- Petersen, George (1 September 2004). "TECnology Hall of Fame, 1877-1950: 25 Audio Innovations That Changed The (Pro Audio) World". mixonline.com. Future Plc. Retrieved 26 October 2021.
- "Universal Audio WebZine: Compression Obsession: The Amazing Release Character of the LA-2A". uaudio.com. Universal Audio. June 2003. Retrieved 26 October 2021.
- JBL vintage service manuals. UREI LA-2A service manual. "This Instruction Book was reprinted from text composed by the original manufacturer (complete with errors and exaggerations; for example, the specification for attack time should have been in milliseconds rather than microseconds." Retrieved on October 11, 2009.
- "Top 20 Best Compressors of All Time". Attack Magazine. Attack Magazine. 13 November 2012. Retrieved 10 September 2021.
- Senior, Mike (September 2009). "Classic Compressors: Choosing The Right Compressor For The Job". soundonsound.com. Future Plc. Retrieved 26 October 2021.
- Humberstone, Nigel (March 1997). "Christopher Fogel: Alanis Morissette's Jagged Little Pill". soundonsound.com. Future Plc. Retrieved 26 October 2021.
- Zoppa, Matt (30 September 2019). "An Analysis of Nirvana's Nevermind". medium.com. Matt Zoppa. Retrieved 26 October 2021.
- Tingen, Paul (June 2007). "Secrets Of The Mix Engineers: Serge Tsai - Inside Track - Shakira and Wyclef Jean: 'Hips Don't Lie'". soundonsound.com. Future Plc. Retrieved 26 October 2021.
- James, Rob (October 2002). "Review: Universal Audio UAD-1" (PDF). resolutionmag.com. resolution. Retrieved 26 October 2021.
- "Universal Audio LA-2A Classic Leveler Collection Review". musictech.net. MusicTech. 15 May 2013. Retrieved 26 October 2021.
- Rudolph, Barry (1 April 2000). "Bomb Factory Digital: "Classic Compressors" Plug-ins For Pro Tools". mixonline.com. Future Plc. Retrieved 26 October 2021.
- Cooper, Dan (26 October 2018). "Our List Of Top LA-2A Compressor Plug-in Emulations & Recreations You Should Try In Your Next Mix". pro-tools-expert.com. Production Expert. Retrieved 26 October 2021.
- Stanfield, Geoff (March 2015). "Waves: CLA-2A & CLA-76 compressor/limiter plug-ins". tapeop.com. Tape Op. Retrieved 26 October 2021.