Universal Audio 2-610 Review

Back in the middle of the 20th century, you couldn't just walk into your neighborhood audio store and buy a mixing console. Generally speaking, mixers

Back in the middle of the 20th century, you couldn't just walk into your neighborhood audio store and buy a mixing console. Generally speaking, mixers were custom units designed and built by the recordists (that is, engineers) that used them. One such engineer was Bill Putnam Sr., who also designed the famed 1176 and LA-2A compressors recently reproduced by the revived Universal Audio company.

Putnam's tube-based 610 was the first modular console (one in which individual channels can be removed for repair while the board remains in service). But more importantly, the 610 sounded great. The few models still in use are highly coveted collector's items steeped in audio history. New generations of Frank Sinatras and Brian Wilsons can now experience some of the 610 vibe, spiffed up with modern innovations such as phantom power and DI inputs, in the Universal Audio 2-610 2-channel tube mic preamp.


Retro styling, along with the less visible benefits of old-fashioned build quality, are obviously high priorities at the new Universal Audio. With its cool purple jewel lamp and big black knobs, the 2-610 looks like a museum piece right out of the box. Weighing almost 12 pounds, the solid metal 2-rackspace chassis seems meant to last well into the next millennium. The gray and black color scheme makes it clear that Universal Audio isn't buying into modern graphics trends. The enclosure is well ventilated at the top, and heat is minimal for a device of this type. A peek at the interior reveals quality parts, a large torroidal transformer, American-made General Electric 6072A tubes, and 12AX7a tubes silk-screened with the Universal Audio logo.

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

The 610's straightforward rear panel has three balanced XLR jacks (mic input, line input, and line output) for each channel, an IEC power-cord jack, a fuse holder, and an AC voltage-selector switch. It lacks insert jacks and has no provisions for -10 dBV operation.

Each set of channel controls on the front panel is delineated by a raised rectangular section; the two sets are separated by the company logo, AC power switch, and individual 48V phantom power switches located in the center of the panel. Individual channel controls are simple and arranged in a spacious, orderly fashion with the massive Master Level knob (marked numerically from 0 to 10 with intermediate dots) as the centerpiece. According to Universal Audio's David John Hinson, that level control is located in the circuit between the initial tube gain stage control (marked in decibels: -10, -5, 0, +5, and +10) and the final tube output stage. Hinson also says the negative gain settings were not a feature of the original 610 console circuit but were added for the 2-610.

The unit's two tube gain stages let you achieve a wide variety of tube coloration and harmonic distortion. The manufacturer recommends keeping the Level control set between 7 and 10 and making coarse adjustments with the Gain knob to get the cleanest sound out of the preamp. Incidentally, the 2-610 has no level or peak metering of any kind.

The Gain knob and a Polarity Reverse switch occupy the upper left corner of the channel section. Below those are the ¼-inch DI jack and a 5-position Input Select switch. That control selects either line, microphone, or DI input as the source, with variable impedance settings for mic (500Ω and 2 kΩ) and DI (47 kΩ and 2.2 MΩ). As explained in the thorough and well-illustrated manual, variable input impedance can be used to match the source with an appropriate load, as well as to subtly adjust the tonal characteristics of some microphones and electronic instruments. All input and output signals pass through custom-designed transformers.

An equalization section is located to the right of the Master Level knob. High-frequency shelving values are switchable between 4.5, 7, and 10 kHz, with boost and cut available in 1.5 dB increments between -9 and +9 dB. Similar cut and boost increments are available for low-frequency shelving, with corner frequencies switchable between 70, 100, and 200 Hz.


During its stay at my Guerrilla Recording studio, I put the 2-610 through a workout on a variety of instruments and musical styles. Despite the unit's impressive pedigree as a component of classic vocal tracks, electric-guitar recording was the main application in which this preamp consistently stood out. Engineer Bart Thurber (who shares the studio and records mainly punk and alternative bands) was the first to rave about the way the 2-610 handles loud guitar. After I tried the unit on a jazz guitarist, Thurber and I excitedly swapped tales about the 2-610's tube magic on all kinds of amplified-guitar tracks. Adjectives such as “creamy,” “beefy,” and “unbelievable” came up repeatedly in our lavish praise sessions, and the 2-610 quickly became the new studio favorite for guitar tracks.

On a guitarist playing a Gibson 175 through an assortment of Fender tube amps, a Royer Labs R-121 ribbon mic took on unexpectedly huge dimensions when coupled with the 2-610. The recorded tone was luscious and thick with a powerful, dominating midbass richness that was inescapable on even the smallest monitors. The 500Ω input setting worked best with the Royer mic; a Sennheiser MD-421 dynamic (placed next to the R-121 as a secondary mic on the cabinet) sounded more transparent at the 2 kΩ mark. Typically, the higher (2 kΩ) input-impedance setting produces less input gain (as much as a 5 dB reduction), as well as subtle differences in frequency response. Such timbral changes are largely dependent on the microphone and its response to changes in impedance loading. In particular, ribbon mics such as the R-121 and the Coles 4038 really shine when coupled with the 2-610's 500Ω input.

On this session, the R-121 and the MD-421 exhibited plenty of bite, and a 1.5 dB boost at 4.5 kHz was all that was needed from time to time to add a bit more cutting power. On other electric-guitar and -bass tracks, a 1.5 dB boost or cut in the low end was always sufficient to produce noticeable thickening or thinning.

The 2-610 played a major supporting role on a project by the band Lower Forty-Eight. On all of the backing tracks, guitarist Andy Lund's cabinet was double-miked (with the R-121 and the MD-421), and many parts were subsequently doubled, resulting in as many as four tracks of 2-610-flavored guitars. The 2-610 captured one of the most gorgeous and stunningly powerful rock-guitar sounds I have ever heard — and I have recorded literally hundreds of guitarists. Electric bass also seems to thrive through the 2-610, and I generated superb depth and definition by taking the instrument direct, both through the 2-610's DI input and using a Manley Tube Direct Interface patched into the 2-610's mic input.


On a couple of occasions, I paired the 2-610 with a Neumann KM 183 small-diaphragm omnidirectional mic on acoustic guitar. The combination was pristine and predictably warm, though in one instance the 2-610 didn't provide enough high-end sparkle in the mix. Switching to a Grace 101 transformerless, solid-state preamp made a world of difference by bringing out the highs and a sense of immediacy the 2-610 lacked. However, with a brighter close mic (a Neumann CMV 563 with the M55 omni capsule) on a different guitarist, the 2-610 successfully captured a cool 1960's-era rhythm-guitar sound.

For a range of other acoustic instruments, including wood and metal percussion, alto and tenor saxophones, and trumpet, the 2-610 was characteristically warm and euphonious. Some louder percussive sources tended to compress or lose their transient sharpness when too much gain was applied; however, moving the mic back or notching down the gain restored the edge.

I was surprised that the 2-610 didn't work to my satisfaction on an acoustic jazz bass recorded with the MD-421. For that application, the preamp was simply a bit too warm and lacking in high-end definition. Compared with other tube preamps I regularly use, the combination of the 2-610 and the MD-421 seemed to pick up excessive room sound, probably due to tube compression. Noise was never a problem on the delicate acoustic sounds, and the 2-610's rated 61 dB of output gain was sufficient for all sources.


On its first vocal outing, paired with a Lawson L47MP tube mic on a folksy male singer, the 2-610 exhibited a bit too much tube splatter on sustained notes and sounded overly grainy in the high end and noticeably compressed. On other singers as well as on a few saxophonists, I observed similar results ranging from graininess to audible distortion. In those instances, I was generally using high-output, large-diaphragm tube mics such as the L47MP or Manley Cardioid Reference.

Thurber related problems he had pairing the 2-610 with a Neumann TLM 103 (which has a hot output). But he did on occasion capture “a little extra edge” on vocal tracks (primarily sung by loud rockers) by coupling the 2-610 with the Lawson L47MP.

In most of the aforementioned cases, the 2-610 gain was set at its minimum -10 value and the Master Level knob was set between 7 and 10. The preamp output was routed directly to analog tape at +4 dBu. Decreasing the Master Level knob did little to alleviate the distortion, indicating a potential problem with headroom at negative gain settings in the 2-610's initial input stage. Whatever the cause may be, the 2-610 wasn't always a prime candidate for vocal recording with tube mics. In my experience, vintage Ampex and Telefunken V72a tube mic preamps can also present such problems; often, I'll end up coupling tube mics — at least when they provide adequate tube coloration — with clean, solid-state mic preamps.

I obtained good results on a quiet female singer by using a CMV 563 tube mic with the 2-610 at 500Ω. It still took some fiddling to get rid of vocal grit, though. The best solution seemed to be to set the Master Level knob to maximum, reduce the initial gain, and move the singer back from the mic. Padding the mic's output or increasing the input impedance should also reduce input gain to the 2-610 so as to obtain a clearer, less compressed sound.

I also generated a terrific sound using a Shure Beta 58 with the female singer doing scratch vocals. That inexpensive stage dynamic mic sounded amazingly rich, airy, and expensive through the 2-610. It had no problems with graininess or undesirable coloration; indeed, in a blind test I might easily have mistaken the Beta 58 for a costly tube mic. I was even inspired to use the Shure mic for some of the final vocal tracks.


To get a sense of how the 2-610 stacked up against other all-tube preamp designs, I conducted loudspeaker tests using a Neumann KM 140 positioned on a full-range monitor playing music in a variety of styles. The 2-610 definitely matched or beat the competition. Up against a modified Ampex 350 series preamp, the 2-610 supplied a tad less high-end sizzle but conveyed more solid and extended bass response. I noted similar results when comparing the 2-610 to a vintage Telefunken V72a tube pre: the V72a offered a more aggressive sound but much less roundness and depth in the low end. Finally, compared with a Peavey VMP-2 (an excellent 2-channel tube pre that costs less than $1,000), the 2-610 proved vastly superior in both high-end detail and low-end punch.

Just for fun, I pitted the 2-610 against a selection of renowned solid-state preamps. Although transistors and op-amps offer distinct differences in upper-midrange and treble clarity, nothing in my racks could beat the 2-610's authoritative and deep lows.

I also compared the 2-610's dual channels with each another. One side (the channel I used for the loudspeaker tests) had a bit more low-end depth, and the other was slightly sweeter sounding and exhibited smoother upper mids. In addition, when setting the Level knobs for identical output gain, the two channels seemed to differ by as much as a half a point on the knobs, depending on the program material and input gain. Fortunately, the Level controls are continuously adjustable, so that was not a big problem; however, my observations underscore the differences in consistency and calibration between tube and solid-state circuits — a concern for critical stereo-recording applications.


The ability to go line level into the 2-610 is an exciting and seductive feature. In that mode, the signal continues to pass through the transformers, the tubes, the polarity-reverse circuit, and the equalization section, making the 2-610 extremely useful for coloration of tracks or stereo mixes. I even used it to salvage overhead drum-mic tracks that had phase problems and a thin sound.

On stereo mixes, the -10 gain adjustment combined with maximum settings on the Master Level control yielded clean and relatively uncolored results. As with most high-quality tube gear, the 2-610 seemed to expand the highs and lows a bit and gave the mix a creamier and slightly compressed finish. Raising the gain and decreasing the level added more tube coloration; at the +10 gain value, it was possible to get deliciously nasty distortion on line-level tracks or mixes. But at those extreme settings, the two channels of my demo unit didn't compress equally, which created minor difficulties in stereo-level matching.

Generally, the 2-610's high-shelving EQ is especially useful for adding crisp detail at the 7 and 10 kHz settings. The high-shelving EQ sounded smooth and sweet when applied in small increments, but Thurber and I agreed that boosts of more than 4.5 dB became overbearing and harsh sounding.

The 2-610's low EQ is certainly powerful in additive as well as subtractive applications; however, a single 1.5 dB click in either direction can sculpt the low end drastically. On some mixes, for example, the smallest available bass boost (+1.5 at 70 Hz) was excessive and made the kick drum sound too thuddy. Although that might be just the thing for warming up a chronically thin mix, for subtler mastering corrections, the 1.5 dB increments were too coarse. Fortunately, on most mixes, just running the signal through the 2-610 provided a deep and satisfying low-end boost, even without EQ engaged.


Using a time-honored tradition of tubes and transformers, the Universal Audio 2-610 adds an authentic old-school glow to all kinds of miked sources. This versatile preamp also is a good value when you factor in the vintage vibe, the dual channels, and the unit's unique ability to do double-duty as both a tracking and a mixing tool. Any recording can potentially benefit from line-level tube-stage processing, and with the 2-610 there is an undeniable fun factor in doing just that.

The 2-610 has been an absolute smash hit for guitar and electric-bass recording at my studio. Indeed, it's hard to imagine doing another rock, jazz, or blues session without it. I am concerned, though, that the 2-610 is not clean enough for all vocal styles, especially when used with a high-output condenser microphone. Moreover, although a Neumann U 47 or a AKG C12 through the original 610 console is considered by many the ultimate signal path for vocal recording, with the unit I reviewed, my recording skills, and an assortment of tube mics and singers, the creamy vocal sounds of yesteryear rarely materialized.

As with most classic tube designs, users should not expect the 2-610's abundant sonic personality to be perfect for all applications. Nonetheless, the unit can work magic on amplified instruments, electronic keyboards, strings, horns, and percussion and in ambient-miking applications. I also highly recommend it for use with ribbon and other low-impedance microphones.

Myles Boisenis a guitarist, producer, composer, and head engineer at Guerrilla Recording and the Headless Buddha Mastering Lab in Oakland, California. E-mail him atmylesaudio@aol.com.

2-610 Specifications Input Connectors (2) XLR balanced mic; (2) XLR balanced line; (2) unbalanced ¼" instrument Output Connectors (2) XLR balanced Maximum Gain 61 dB Maximum Input Level (mic) +3.5 dBu Maximum Output Level +20 dBm Microphone Input Impedance 500Ω, 2 kΩ (selectable) Hi-Z Input Impedance 2.2 MΩ, 47 kΩ (selectable) Frequency Response 20 Hz-20 kHz (±1 dB) Dynamic Range 100 dB THD 0.25% at minimum gain; 0.40% maximum gain (at +4) Signal-to-Noise Ratio >82 dB (at maximum gain 61 dB) High-Frequency Shelving EQ Boost/Cut 1.5, 3, 4.5, 6, 9 dB (switchable) Low-Frequency Shelving EQ Boost/Cut 1.5, 3, 4.5, 6, 9 dB (switchable) High-Frequency Shelving EQ Corner Frequency Select 4.5 kHz, 7 kHz, 10 kHz (switchable) Low-Frequency Shelving EQ Corner Frequency Select 70 Hz, 100 Hz, 200 Hz (switchable) Power 48V phantom power, DC (switchable per channel) Tube Types (2) 12AX7a; (2) 6072A Power Requirements 115V or 230V (switchable) Dimensions 2U × 12.125" (D) Weight 11.75 lb.


Universal Audio
tube mic preamp



PROS: Rich tube sound. Quiet. Variable impedance on mic and DI inputs. Line-level input capability with access to all features. Polarity reverse. Onboard EQ. Well-built.

CONS: Difficult to set gain for adequate headroom on some high-output microphones. No level or peak metering. Stereo channels not perfectly matched.


Universal Audio
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