If I were to list my five favorite analog processors of all time, the Universal Audio LA-2A leveling amplifier and 2-610 tube preamp would easily make the list. I often chain them in series to record tracks in my studio. And so I particularly relished the thought of reviewing the company's new all-tube LA-610 channel strip, which combines a modified channel of the 2-610 with an LA-2A — style optical compressor. The 2RU LA-610's rear panel sports separate mic, and line inputs and a line output on balanced XLRs. A high-impedance (instrument DI) input is accessed via an unbalanced ¾-inch phone jack on the front. The compressor section does not have a sidechain input.
The unit's custom I/O transformers are the exact same ones used in the 2-610. However, the unit's preamp circuitry departs from a 2-610 channel in significant ways: Two 12AX7 tubes serve the LA-610's two gain stages, as opposed to one 12AX7 and one 6072 per 2-610 channel. (The 2-610's 6072 tube output stage has been moved in the LA-610 to serve its compressor's makeup gain.) The LA-610 also includes a 15dB pad on its front panel, a feature I wish the 2-610 also had, considering the latter's limited headroom. The LA-610's preamp is also voiced to have a slightly more prominent high-frequency response than the 2-610.
The LA-610's preamp section features a five-position rotary switch that selects among line, mic and DI inputs, with the latter two each offering a choice of two different input impedances: 500 ohms or 2 kilohms for mic input, and 47 kilohms or 2.2 megohms for DI. A five-position gain control adjusts the gain of the preamp's 12AX7 input stage in 5dB increments. As you turn this switch clockwise, negative feedback is reduced and gain increases along with pleasing harmonic distortion. A separate level control serves the 12AX7 output gain stage. Total maximum preamp gain is a respectable 61 dB. Joining the 15dB pad are toggle switches for 48-volt phantom power and polarity reversal.