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Volume 1, Number 8, November 2003
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Compression Obsession: Living in LA: LA-3A, LA-4, & LA-5

After the success of the LA-2A, the original el-op compressor design began a journey through several iterations that eventually ended with the LA-5; Later, the LA-2A again lent its prefix to another UREI family of VCA-based gain control devices: the LA-10, LA-12, and LA-22. Of all of the optical compressor kin, the LA-3A is probably the most desirable, famous and still widely used offspring to develop from that great design. If you have ‘em, you already know they’re awesome. Don’t let ‘em go to waste! The used market is getting scarcer and pricier for these gems.

Teletronix/UREI LA-3A
The LA-3A made its debut at the 1969 NY AES show. It was designed by Brad Plunkett, who also played a major role in the development of the 1176. Essentially, the LA-3A is a solid-state version of the LA-2A; It retains the same simple control set, and- of course- the all-important T4 el-op module, which was the source of all the great program-dependent compression characteristics for the LA-2A. Interestingly, the LA-3A also retained the Teletronix name when first released. With the new design, the LA-3A had a similar sound to the LA-2A, but was housed in a space-saving 2U, half rack unit.

UREI/Universal Audio LA-3A
Some say the LA-3A is sonically like a cross between an LA-2A and an 1176. The LA-3A has solid-state discrete circuitry and balanced inputs and outputs. The LA-3A saw no significant design changes in its run through 1981.

If the LA-3A is an LA-2A with a little 1176 thrown in, then the LA-4 is the other way around, in terms of functionality and feel. With a double pot design in the primary controls, the LA-4 allowed the user to select between ratios of 2:1, 4:1, 8:1, 12:1, and 20:1. It also reversed the orientation of the primary controls, and renamed them “threshold” and “output”, bringing the feel closer to an 1176. However, the LA-4 still retained the optical design and did not bring in controls for attack and release.

The LA-4 also saw the end of the class A design, and the introduction of an early integrated circuit (IC) chip. The LA-4 also added the convenience of front panel switching to allow for stereo linking and un-linking of two units--Very convenient, considering that the LA-3A and LA-4 were often used as stereo devices. The most interesting change however, is the introduction of an LED based optical design, which I’m certain was a
Universal Audio/UREI LA-4
cost saving measure, and may have combated the “panel aging” factor found in the original T4 (It was originally recommended that T4s be periodically replaced, just like tubes). (See July's Compression Obsession for more info about T4s and “panel aging”).

Around 1980 the LA-4 received more design changes as well as a component upgrade of the original ICs. The LA-4 had a run from 1977 to 1989 and saw blackface and silverface iterations.

UREI/Universal Audio LA-5
Later came the LA-5 … essentially a “stripped” LA-4 with the removal of the ratio controls and a fixed ratio of 20:1, and the removal of stereo link capabilities. The LA-5 only saw the silverface era. It appears the LA-5 was aimed at the live sound community as speaker protection from overloads.

--Will Shanks

Much appreciation to Everett Watts for the help!

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