One company that's helping to keep tube technology alive is the reincarnated Universal Audio (UA), founded by the offspring of legendary engineer and
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FIG. 1: Universal Audio''s LA-610, a channel-strip unit, combines a 610 mic pre with a tube compressor, EQ controls, and multiple inputs.

One company that's helping to keep tube technology alive is the reincarnated Universal Audio (UA), founded by the offspring of legendary engineer and original UA founder M. T. “Bill” Putnam Sr. One of UA's missions is to re-create products such as the Teletronix LA-2A tube compressor and Putnam designs such as the UREI 1176 solid-state compressor and the original Universal Audio 610 Tube Microphone Preamp.

The acclaimed 610 mic pre design has made its way into several of UA's reissued products, and now it has been combined with a tube compressor to form the LA-610 channel strip. Its leveling amplifier section offers the features of the pricey LA-2A, and with its EQ section, multiple inputs, and tube-based architecture, the LA-610 is a vintage-style console strip that you can tuck under one arm.

Modular Makeup

Although it is strictly a single-channel device, the LA-610 conforms to the layout of UA's 2-610 and 6176 two-channel processors. A pair of modules occupies the front panel of this 2-rackspace unit, with the preamp controls on the left (see Fig. 1). A five-position switch on the front panel's lower-left side determines the active input. The switch can be set to Mic (500 or 2kΩ), Line, or Hi-Z (47kΩ, or 2.2MΩ).

Above that control is the input-stage Gain knob, one of three gain controls on the LA-610. The input gain control can be adjusted in 5 dB increments (-10 to +10 dB). The large 1½-inch-diameter level knob in the center of the panel is a trim control that reduces the output of the LA-610's gain block before the signal reaches the compressor section. The level knob is encircled by calibration marks (not decibel measurements) ranging from 0 to 10.

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Go to the Focus on Universal Audio page to see video and learn more about UA products

In keeping with conventional gain staging practice, the cleanest preamp signal is achieved by setting the input gain as low as possible and keeping the level knob close to its maximum value. Keep this principle in mind when using the LA-610, because the preamp is always in the signal path, as is the compressor's makeup gain stage.

Between the two gain pots is a vertical row of three switches for -15 dB mic input pad, polarity reverse, and 48V phantom power. At the bottom of that row is a ¼-inch input jack for DI signals. High- and low shelving equalizers are on the right side of the module. Each shelf band has three switchable frequency settings: below 70, 100, and 200 Hz (low); and above 4.5, 7, and 10 kHz (high). Two EQ gain knobs provide a boost or cut in a range from -9 to +9 dB.

Welcome to LA

The compressor module of the LA-610 features the same simple leveling amplifier controls as those of the LA-2A and its solid-state offspring, the UREI LA-3A. One large knob governs peak reduction, and the other controls makeup gain. Behind both pots are indicators marked 0 to 10. A three-position mode switch offers a choice of compressor bypass (the makeup gain stage is always active), compression (lower ratio), and limiting (higher ratio).

Beyond those parameters, the characteristics of the LA-610's compressor are determined by the behavior of its T4 electro-optical sensing cell. That cell uses the light-sensing properties of a photoelectric cell paired with a luminescent panel to generate the compressor's control voltage. The T4, which is also the brain of the LA-2A and LA-3A, adds its own unique attack, release, and knee qualities to the compressor.

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FIG. 2: The LA-610''s rear panel has only +4 balanced XLR connections: one line output, one line input, and one mic input.

The three-position knob on the LA-610's compressor module selects the source for the meter on the faceplate's upper-right side. This meter can register the VU output of the preamp or compressor, or it can indicate gain reduction. The unit's AC power switch, purple jewel lamp, and logo reside below the meter, on the panel's lower-right corner.

Because any signal entering the LA-610 passes through the preamp and compression modules, the rear jack panel (see Fig. 2) contains only a mic input and +4 balanced line input and line output connectors (all XLR). There aren't any options for -10 dBV consumer-level operation, and inserts are not included.

A standard IEC power-cord connector and a fuse assembly are the only other rear-panel elements. The LA-610's housing is of sturdy all-metal construction and provides adequate venting for its five tubes (three 12AX7s, one 6072, and one 6AQ5).

Tube Testing

The two-channel UA 2-610 has been my favorite preamp for electric guitar since I reviewed it in the February 2002 issue of EM (available online at www.emusician.com). Detailed tests of the 610 module and comparisons with similar products can be found in that review.

The 610 preamp is tough to beat for adding harmonic richness, thickening the low end of the sonic spectrum, and subtly smoothing and compressing — all hallmarks of a quality tube sound. My main criticism of the 2-610 is its tendency to distort on high-gain mic input signals. UA addressed that problem on single-channel 610 versions by adding a -15 dB microphone input pad.

Because the preamp side of the LA-610 is implemented differently from the twin preamps of the 2-610, I wanted to compare the sound of both units. On a Fender bass (DI in, 47kΩ) the 2-610 had a rounder, mellower sound. The LA-610 brought more presence to the upper mids and was clearer as a result.

With a full-range mix applied to the line-level input, the 2-610 had more punch and depth in the low end, while the LA-610 favored upper-mid range elements such as tambourine and female vocals. I discovered later that this high-end emphasis — as mentioned in the LA-610 manual — is designed to compensate for treble attenuation within the T4 optical cell. Although the basic personalities of these two preamps are consistent, my ears told me that the 2-610 is richer and warmer overall, while the LA-610 exhibits more tube character and an upper-mid range edge.

In all trials I minimized excess coloration by keeping the final make-up gain at about 5.5, which is unity according to the onboard meter. Running the preamp at a lower level and taking care to keep the VU readings on the conservative side yielded cleaner audio. The LA-610 should never run out of extra output gain, because the unit can boost line level signals by 40 dB and pump up mic levels by a whopping 77 dB.

The LA-610 got a thorough workout as the front end on a Pro Tools session by composer/multi-instrumentalist Fred Frith. The preamp imparted trademark tube tone to Kurzweil keyboard patches and was particularly creamy on slide guitar and rock chording. Frith's electric bass was rendered with especially rich overtones, drawing appreciative comments from the artist. Light peak compression applied to that DI bass part was transparent and clean, but the unit was prone to mild distortion and a thinning of the low end once constant gain reduction was applied.

I tried the Channel Strip again on sessions with several electric bassists (myself included), and the unit always required careful attention to gain staging and headroom. On the other hand, when a fellow engineer requested my help with a Digital Performer mix plagued by excessive mid range in the acoustic bass track, the UA made me look like a hero. Once levels and compression were set, this discerning client echoed a judgment I have made many times, remarking that the bass tone was better as soon as it passed through the 610.

Obstacle Course

During the course of a few months of sessions, the LA-610 proved its worth on a variety of instruments. It complimented ribbon mics beautifully at the 500 input setting, graced a sensitive jazz trumpet ballad, and deftly tamed an overly dynamic synth part. My studio partner Bart Thurber gave it the thumbs up for rock-guitar recording and confirmed that the LA-610 was a shade brighter in timbre than the 2-610. Both of us took a shine to the optical compressor for electric- and acoustic-guitar enhancement in mixing.

The LA-610 compressor stood up to the competition in a studio that included vintage UREI LA-series compressors and an LA-2A clone. With its multiple tube stages it can take some time to get the sonic seasoning just right, especially because the tubes do contribute their own compression flavor.

In general, I preferred the LA-610's dynamic squeeze at moderate gain reduction settings which, given the unit's nonadjustable attack and release parameters, kept the compression effect smooth and transparent. On line-level input, steady gain reduction of 3 dB on the VU meter contributed overdrive grit, whether in the compress or limit mode. Switching between the bypass, compress, and limit modes produced no audible timbre change or switching noise in the audio.

With the 2-610, I have gotten some wonderfully rich results on vocals. On a few sessions with male singers using large-diaphragm tube mics, however, the LA-610 tube treatment turned to vintage vocal crunch. When partnered with a tubey Lawson L47MP or the low-coloration Blue Bottle, the LA-610 prompted comments such as “veiled,” “slightly fuzzy,” and “distorted, even with minimal compression.” On a spoken-word session with female vocal talent using a solid-state Neumann U 87, the LA-610 delivered a pleasantly warm track.

On the Bright Side

With its combination of tube mic pre, DI, line-level input, 2-band EQ, and optical compressor, the LA-610 has the character and features to meet a broad range of studio needs. It does its job while providing vintage appeal, yet the sticker price is low for a channel strip with UA's handmade quality.

Even first-time tube-gear users will have no trouble hearing that the LA-610 is all about tube timbre. But no tube preamp or compressor is perfect for all applications. I still preferred the 2-610 for certain duties.

The addition of an input pad is a big improvement in terms of keeping microphone signals clean. During months of use, however, I learned to approach the LA-610 package with caution when setting gain and/or compression, especially with vocals, with widely dynamic sources, and when using it as a DI for electric bass.The compressor side worked best at low-impact settings and was particularly vulnerable to thinning or grittiness when pushed too hard.

With certain sources and microphones, the LA-610's sound is pure tube magic. Fortunately, the LA-610 incarnation of the 610 pre is still a knockout for electric guitar recording. I highly recommend the unit for use with solid-state condensers and ribbon mics. The LA-610 also makes a superb line amplifier capable of enhancing and gently compressing digitally recorded signals.

Myles Boisen can often be seen huddled over the warm glow of all-tube hardware during those long winters at Guerrilla Recording in Oakland, California.


Analog Inputs (1) balanced XLR (line);
(1) balanced XLR (mic);
(1) ¼" TS (instrument) Analog Outputs (1) balanced XLR (line) Input Impedances Mic, 500Ω or 2kΩ; balanced line, 20kΩ; Hi-Z, 2.2MΩ or 47kΩ Maximum Microphone Input Level (at 2 kΩ, 15 dB Pad in) +14 dBu Maximum Output Level +20 dBu Frequency Response 20 Hz-20 kHz, ±0.5 dB Maximum Gain 40 dB (Line), +77 dB (Mic) Noise Floor (line in, unity gain) -72 dBu, 20 Hz-20 kHz Tubes (3) 12AX7, (1) 6072, (1) 6AQ5 Power Requirements 115V, 230V operation Dimensions 2U × 12" Weight 12 lbs.


LA-610 tube channel strip $1,749


PROS: Vintage-reissue tube mic pre and tube compressor. Multiple-impedance mic input. Hi-Z DI input. VU meter. Significant tube coloration. Abundant output gain.

CONS: Mic pre and compressor cannot be accessed separately. Excessive input level, improper gain staging, or too much compression can cause distortion.


Universal Audio