Audio Research I/50 Integrated Amplifier Review

Posted on 8th February, 2023

Audio Research I/50 Integrated Amplifier Review

John Pickford auditions a surprisingly affordable high-end integrated valve amplifier…

Audio Research

I/50 Integrated Amplifier

From US$5,000 RRP

There are those who believe that valve amplifiers should have been consigned to the history books sometime around 1970, and there are those who know better. For it was in 1970 that Minneapolis-based manufacturer Audio Research launched its first products, powered by supposedly obsolete vacuum tubes. But as the resurgence in vinyl has proved, perfectly good tech, once considered redundant, has a habit of bouncing back…

Audio Research's I/50 integrated amplifier represents an entry-level into the company's 'High Definition' amplification range. While it may seem like an eye-wateringly high price for an entry-level item, the company does not identify as a budget brand – and the new I/50 could easily be another manufacturer's flagship product.


Our review sample is the standard line-level amplifier. However, an optional phono module for moving magnet and high-output moving coil cartridges, plus a DAC module are also available. This is a high-quality DAC/Ethernet streamer with Roon Ready status, so a fully equipped I/50 will take care of all vinyl replay and hi-res streaming duties.

The amplifier itself offers 50 watts of push-pull power from two matched pairs of premium Sovtek 6550WE tubes, while the preamp stage uses a trio of 6922 triodes. A rubber tube ring is fitted to the centrally placed 6992 valve for the pre-gain stage to prevent microphony. The other triodes are used in a different part of the circuit and not subject to microphonic problems, hence no need for tube rings, says the manufacturer.

As the amplifier is sensibly shipped without the valves in situ, they need to be fitted before use – but don't let that put you off, as each tube is clearly marked, so that fitting into the correct slot is foolproof. A protective cover for the valves has to be removed to gain access to fit them, and a nice touch is the bespoke screwdriver supplied for the job.

Once the valves are correctly fitted, the cover can be either refitted or left off to enjoy the warm glow of the valves, just as long as safety is not an issue – valves do get hot and could easily burn inquisitive fingers. 

Newcomers should also be aware that valves have a finite lifespan, with Audio Research suggesting the 6922s are good for around 4,000 hours while the 6550s have approximately half of that life expectancy. When a new set of valves is installed, a qualified technician will be required to adjust the bias, as there is no user adjustability for this job. 6550s cannot be replaced with other types of power tube such as KT88s, so this amp isn't for tweakers. 

Six different colour schemes are available, with black and silver providing a more traditional look, while red, yellow, blue or white units cut a decidedly funky dash. These colours are replicated on the Mondrian-inspired cover of the rather lovely manual that comes with the amp.

Adding to the visual appeal are two proprietary LexieTubes, which provide display information for source selection and volume. This display can be dimmed but not switched off entirely when the amp is powered up; however, when powered down but still plugged into the mains, the LexieTubes each show a small green dot. Not being a fan of digital displays I would've liked the option to switch off the display or at least just see the green dots rather than be permanently reminded of the volume level in numerical form. 

Either side of the LexiTubes is rotary controls, one to select the input source and the other to adjust volume. Most users, however, will prefer to use the remote control, which is a beautiful item in its own right, the metal casework feeling solid and purposeful in a way cheap plastic remote cannot match.

While we're on the subject of the amp's excellent build quality and finish, I should point out that the I/50 is the first Audio Research product to be finished in-house. The classy Cerakote finish is applied at the company's own painting facility, which also has laser imaging and marling machines.

Also flanking those dazzling LexiTubes on the unit's top plate are the power button and a standard 1/4-inch jack connector for headphones. All other connections are made via the rear panel where there are three line-level RCA inputs – one of which becomes the de facto phono input when the phono module is installed – plus a single pair of XLR inputs to accommodate a balanced source. The chunky speaker terminals are a little different from the norm as they offer a choice of 4-ohm or 8-ohm taps to provide an optimal match for any given loudspeaker.

Upon power-up, the I/50's LexiTube display counts down from 50 to zero before the amp is ready for use, and while a longer warm-up period will subtly improve sound quality, it sings sweetly enough from the get-go. The amp remembers your previous volume setting once operational; however, it will have to be unmuted before you hear sound.

As valve amplifiers go, the I/50 is on the powerful side; its 50 watts per channel of push-pull power is capable of driving pretty much any loudspeaker – unlike most single-ended designs with power ratings in single figures. As such, it made light work of driving my big, sensitive Tannoys, yet didn't flinch when connected to the hideously insensitive (82.5dB) BBC LS3/5a monitors. It was also a match made in heaven with my original Quad Electrostatics, which can kill feeble solid-state amps with its punishing impedance swings.


Potential customers expecting to hear the warmth and colour of a classic valve amp will not find it here with the I/50. There's no fleshing out of the lower midrange and upper bass to add artificial warmth, nor is there obvious colour to give a rose-tinted view of your music collection. This is a good thing. My old Leak Stereo 20 is lovely to listen to, but it doesn't tell the truth, instead sugaring the musical pill with a delicious toffee-flavoured midrange at the expense of true low-end grip and high-frequency extension. 

The I/50 has all of those positive thermionic traits, such as a gloriously open midrange full of vibrant colour (as opposed to sounding coloured), yet it also masters those frequency extremes that most historic valve designs fail to reach. For example, Led Zepplin's Since I've Been Loving You from their third album released in 1970 – the year of Audio Research's launch – illustrates this perfectly. 

I was thunderstruck by the sheer weight and low-frequency foundation of John Bonham's bass drum. Sure, it packs a punch on most decent systems; however, the I/50 driving my Tannoys fully revealed both the impact and body of the sound, illustrating the precise relationship between the attack of the beater, the resonance of the drum and its decay. I was also made well aware that Bonzo's squeaky kick drum pedal could benefit from a liberal spray of WD40!

The amp's ability to portray harmonic texture was immediately apparent when listening to Nick Drake's At The Chime Of A City Clock from Bryter Later, another classic album from 1970. Here, the focus, resolution and transparency of the I/50 were most noticeable in the way it framed Nick's vocal and acoustic guitar with the silky smooth strings and smokey saxophone, making for a more palpable and involving performance.

Although the I/50 replays music with the kind of harmonic definition and timbral finesse that leaves many solid-state amplifiers sounding tonally grey in comparison, it doesn't rely on unnecessary harmonic padding of the sort that gives vintage valve amps an artificial sweetness. Instead, it draws upon its broad tonal palette to paint a musical picture in vivid colours.

There's nothing lush or laid back about the amp's character, rather it majors on musical power and momentum, ensuring it retains control of dynamically dramatic recordings. Black Marigolds by the Don Rendell/Ian Carr Quintet features sections of gentle piano and muted trumpet peppered with explosive blasts of brass, woodwind and percussion that leaves underpowered amps flailing to get a grip. The I/50 takes it all in its stride, though, impressing with the way it reacts to shifts in dynamic range with apparent ease.

Adding to the amp's prowess in portraying tonal accuracy and dynamic contrasts is its natural pace and drive when dealing with strong rhythms. Not 'fast' in the style of leaner-natured amps that promote snappy transients at the expense of body and weight, the I/50 remained agile yet sure-footed when dealing with all types of dance music, whether it was the superfunk of James Brown's JBs or the electronic pop of Saint Etienne


Audio Research has a winner on its hands with the new I/50 integrated amplifier. It won't win any friends among those who prefer their preamps and power amps to be housed in separate boxes along with outboard power supplies. However, it ticks all the boxes for those wanting a no-nonsense, high-quality slice of valve amplification capable of driving almost any loudspeaker. This is especially so when fitted with the optional digital and phono stages. If you've ever wondered about the sonic capability of classic thermionic power, here's a fantastic opportunity to test the tubes.

For more information visit Audio Research

    John Pickford's avatar

    John Pickford

    A professional recording engineer since 1985, John strives for the ultimate in sound quality both in the studio and at home. With a passion for vintage equipment, as well as cutting edge technology, he has written for various British hi-fi and pro-audio magazines over the years.

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    Tags: audio research 


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