Integrated Amplifiers

Keeping it relatively cool-running are side-mounted heatsinks that are turned into something of an artform – Boulder suggests their curves might be reminiscent of trees, but we'd venture an accordion. Regardless, to my eyes it's certainly a smarter-looking amp overall than the 865, with the front fascia now having a slight backwards angle to it, and buttons limited to just volume up/down, mute and standby. It's mostly a doddle to use, with only the Android app's UPnP side throwing up some head-scratching moments during our audition – we had better results with BubbleUPnP.

Easy Rider
This integrated amplifier has a smooth, easy-on-the-ear presentation that's seductive and addictive. And that's true across its various wired and wireless points of entry. The power stage is never in doubt, but the amp balances its speaker-driving ability and dynamism with a real sense of poise. Richly drawn basslines develop beneath a mid and treble that carry plenty of lifelike detail. Nothing jars or sounds out of step. In a word? Sublime.

Led Zeppelin's 'Achilles Last Stand', from the 2015 deluxe edition of Presence [Atlantic/Swan Song; 96kHz/24-bit], is notable because it features John Paul Jones on an eight-string bass guitar, and it's his playing – and John Bonham's immaculate drumming – that's the backbone of this near-11-minute epic. Through the 866, there was excellent detail and definition to Jones' galloping runs, so that they remained distinct even while Jimmy Page was laying on guitar overdubs.

More importantly, the song just sounded right, bouldering along at pace with a sweetness to Robert Plant's evocative vocal and a thump to Bonham's kick and snare. The layered production didn't pose the 866 problems – it conveyed the various aspects with fuss-free aplomb, leaving it clear and clean without dulling the rocking energy. Similarly, on the album's 'Nobody's Fault But Mine', the amp brought smoothness to the slide guitar intro, a powerful blast to the harmonica solo, and heft to the rhythm section.

Pump It Up
These Zeppelin tracks should be presented as gritty and live, but 'Take My Breath', by The Weeknd [Dawn FM; Republic Records 00602445021154], is sparkling and modern by comparison, a mélange of icy synthesisers and electronic percussion. The Boulder 866 lapped it up, putting a spotlight on the (auto-tuned) vocals that soar above the electrofunk instrumentation. It's ostensibly a pop song, but there's a degree of menace to it, something ably conveyed by the 866's ability to lean into its deep, synthetic bass.

On a clean, pure-sounding track like this, the temptation to pump it up is hard to resist, particularly as Boulder's FAQ section ('the amplifier will not be damaged if you play it at max volume') encourages such behaviour. It's easy to find a listening sweet spot, as the 866's digitally-controlled analogue volume provides 100 steps, set by the amp's display or the app. At '92' (or –8 on the dB scale), and with B&W's 703 S3 floorstanders in tow, The Weeknd's piece became a room-filling delight, but with the balance and control shown at lower levels.

Muscle Tone
Indeed, the Boulder 866 has a subjectively pristine presentation. Allied to its abundant energy and transient attack, the result is a sonic signature that worked well with George Harrison's 'Got My Mind Set On You' [Cloud Nine; Parlophone 7243 5 94090 2 3] and 2Pac's 'All About U' [All Eyez On Me; Death Row Records 25242492]. I wouldn't usually consider either of these tracks particularly well produced, but the 866 found the best elements of both, delivering the music with a joyous infectiousness.

So this amplifier plays loud with superb control, while showcasing a sultry sense of tone and texture whether taking an analogue source or a digital stream. But can it cosset you in more delicate soundscapes? American singer Shelby Lynne's 2008 cover of Dusty Springfield's 'Just A Little Lovin', from the album of the same name [Universal Music Group; 192kHz/24-bit] reimagines the song as a late-night jazz club staple, filled with pregnant pauses, long-decaying notes and percussive details, while Lynne becomes a melancholy figure. Your focus is drawn to her exquisite vocal, which mixes breathy passages with pristine enunciation, but as impressive is the staging of the players around her.

On this piece, the 866 painted a picture that was consummately immersive, and it wasn't a one off either – a 44.1kHz/16-bit download of Diana Krall's 'Temptation' [The Girl In The Other Room; Verve Records] enjoyed microdetail clarity (such as the sinewy sound of the upright bass) that belied the 866's price.

Boulder's integrated is therefore an amp for all seasons – as appealing when slipping into a jazz ensemble as it is when hammering out your guitar-driven classics. Helping with all genres is its remarkable handling of the low-end, which throughout my listening steered clear of indistinct bloat. Some listeners might desire a warmer, softer bass but I wouldn't want to upset the fine balancing act Boulder has achieved here. The 866 is rock-solid.

Hi-Fi News Verdict
Some integrated amplifiers might offer slightly more functionality as a system hub, but Boulder's 866 is well specified, impressively built and a knockout performer. This has all the attributes of a muscle amp, but it's not simply power which grabs your attention. Balance, detail and sweetness make listening sessions seriously enjoyable, and in this analogue/digital guise, it brings its talents to all your sources.