As many Audiophile Style readers know, I fell in love with the RAAL-requisite SR1a headphones this year (link). They are the first true ribbon headphones and have very unique power requirements. Other than using one of only two direct drive amplifiers made specifically for these headphones, from Schiit and RAAL-requisite, the SR1a must be driven by a traditional power amplifier. In other words, these headphones connect to a power amplifier's speaker output terminals, with an interface box between the speaker cables and the headphone cable. It's a configuration that I absolutely love because it opens up these headphones to the world of high end amplifiers. Why wouldn't I want to power the most sensational audio product I've ever heard with an amplifier from one of the best companies in high end audio?
With this in mind, I set out to acquire review samples from Parasound, Constellation Audio, and Boulder Amplifiers. Each company offers something unique that really scratched my itch to take the SR1a to the next level. My evaluations of the Parasound HINT 6 and Constellation Audio Inspiration Integrated are ongoing, but I'm finished putting the Boulder 866 Integrated through every test imaginable and listening through it for countless hours. OK, not quite finished listening because I have my headphones on as I type this review. Someone pinch me, the world is close to coming out of a global health pandemic and I'm bathing in sound quality, build quality, and enjoyable musical experiences on an incredibly high level.
A Little Background
A few quick notes on my requirements and why I selected the Boulder 866 Integrated for this review. The SR1a headphones and interface box present a 5.6 ohm load to the connected amplifier. This configuration requires an amp with at least 100 watts and in my experience the amp must be fantastic and without flaws, to make these headphone shine. Think about it this way, have you ever placed your ear right next to a tweeter and listened to the grunge and noise that some amplifiers emit? While that's an experiment done only for kick and giggles, listening to the SR1a headphones is a serious endeavor that places even more extreme requirements on the audio system. Wearing these headphones is like placing one's head less than one inch away from two full range, incredibly transparent speakers, and listening for hours on end. If there's a sonic issue with an amplifier, I will find it using the RAAL-requisite SR1a. Conversely, if an amp is among the best, these headphones will reproduce music on a level that's second to none.
I must also clearly state that using the SR1a headphones with an amplifier like the Boulder 866 Integrated is completely different from connecting other headphones to the quarter inch jack of an integrated amp and letting 99% of the power remain unused. The SR1a are demanding and will push amplifiers as far or farther than a pair of loudspeakers. I know it sounds strange for those who haven't experienced the SR1a, but it's really a special headphone on many levels.
I specifically reached out to Boulder Amplifiers for its 866 Integrated because the unit checked all the boxes I needed for my integrated amp research. I needed a one box solution that isn't too large, offers plenty of power, is designed by extremely competent engineers, supported by a great company, has digital inputs, and looks great sitting next to me on my desk, where I wear my headphones most frequently. I purposely selected other amps for my research that offer different features, that I'll go further into during those reviews.
Boulder 866 Integrated
The Boulder 866 Integrated amp is offered in two configurations, all analog ($12,250) or analog and digital ($14,450). I selected the analog and digital version because I wanted this to be a one box, elegant solution for my headphone system. Visibly, both versions are identical except for the digital inputs on the rear of my review unit. The metal work on the 866 chassis is classic Boulder. It's unique, built like a brick outhouse, and oozes class and quality. Even the buttons on the front panel have a very solid feel to them when pressed. The weight of the 54 lbs chassis also means the unit doesn't budge an inch when pressing the buttons, unlike some components that slide back on a rack or desk when the front panel is touched.
The front panel also features a full color touch screen that displays album art large enough to be seen from across a room. This touch screen also enables one to configure the unit in a limited way if needed. I recommend using Boulder's iOS app for configuration and adjusting this front panel display because it provides options unavailable directly on the display. For example, using the iOS app I added custom icons for the analog inputs, that displayed logos for Berkeley Audio Design, dCS, and EMM Labs. All companies whose DACs I connected to these inputs during this review. One thing that shouldn't be overlooked is the simplicity of the touch screen and iOS app interface. This is an incredibly easy device to use and setup.
Prior to writing this review I interviewed the Boulder team about the 866 Integrated and gleaned a bunch of information that I know is of interest to the Audiophile Style Community. First and foremost is the Raspberry Pi 3 B+, single board computer that handles some of the 866's digital duties. Previous Boulder components have used the Beaglebone platform, but the 866 has additional requirements that made the Beaglebone too underpowered for this application. Like all Boulder digital components, in the 866 the company opts to digitally oversample the audio prior to delivery to the DAC chips. All audio that enters the 866 via Ethernet or via USB hard drive (PCM and DSD) is oversampled by the Raspberry Pi 3 B+ to 24 bit / 352.8 kHz using Boulder's proprietary algorithms. Thus, the need for a more powerful single board computer than the Beaglebone. Audio that enters the 866 via AES or Toslink is oversampled via FPGA rather than routing this signal back through the Raspberry Pi.
The Raspberry Pi based Ethernet input is Roon Ready (certified) and can accept DLNA streams from any DLNA compliant server. Attaching a hard drive to a USB port of the built-in Raspberry Pi enables one to browse the music stored on the drive, via the iOS app, but the experience leaves a lot to be desired. I use the 866 Integrated as a Roon Ready endpoint for 99% of this review period.
The Ethernet interface of the 866, handled by the Raspberry Pi, had no problems accepting audio up through 24 bit / 352.8 kHz. I experience zero pauses or stuttering during playback. I also tested the built-in wireless capability and had surprisingly great results. The 866 has no visible WiFi antenna, leading me to believe it would be somewhat limited to lower sample rates. I successfully played DSD64 and up through 24 / 352.8 without a single hiccup via wireless. Technically the unit can accept up through 384 kHz, but I couldn't find any of my 384 content to test. Also of note, the unit's maximum DSD rate is DSD64. All DSD content above this is resampled by Roon to DSD64.
Like all Boulder products, the 866's volume control is purely analog. It's controlled digitally, but at no time is digital attenuation used. Along similar lines, the analog signal, from the three XLR inputs, remains in the analog domain the entire time. The volume control is a design developed by Boulder and improved over many years. The main difference between the 866 volume control and that of the 2000 series products is that the 866 doesn't have fully differential attenuation. The reason for this is because good analog volume controls cost a lot of money and Boulder needed to decrease the cost of the 866 relative to its higher end products.
One aspect I found interested, when talking to the Boulder team, was that they learned quite a bit designing this product. Most Boulder products are cost-no-object type of designs that have a completely different set of engineering decisions to make. The 866 Integrated forced the team to get creative and try new things that in the end turned out to be great for the 866 and possibly other Boulder products. Dare I say there could be a trickle-up effect.
Enjoying the Sound
Listening to my RAAL-requisite SR1a headphones through the Boulder 866 Integrated was a tough job, but somebody had to do it. Only joking of course. This is the part of my job that causes me to thank my lucky stars. I had to listen to the best headphones in the world being driven by a fantastic amplifier, for hours on end. Oh the horror.
Getting right to the point and throwing the 866 Integrated right into the fire, I played Passacaglia from the Kansas City Symphony, recorded by Reference Recordings' Keith Johnson. I encourage everyone to play this track on their systems. Turn the volume up all the way and have a listen. People may not like what they hear on many systems. Through the Boulder 866 Integrated, I heard nothing but incredible detail, noises that were captured on the recording but not part of the performance, and a fantastic string section. This isn't the style of music I usually listen to for pleasure, but I often use it as a laboratory tool to put a components performance on display. Some components wilt on this album and can't handle the incredible dynamic range and detail. The Boulder 866 Integrated sailed through the test, reproducing absolutely everything on this recording without adding anything, even with the volume set to 100 for some passages.
Switching to music that really moves me, I put on Blow Up from the Isao Suzuki Trio recorded for the Three Blind Mice record label. Track one, Aqua Marine, is a delight for the ears with both high and low frequencies that have texture crystal clear qualities. The Boulder 866 Integrated reproduced this tracks on entire album wonderfully. One sonic difference between the 866 and some other amplifiers I've heard in my room is that the 866 sounds a skosh darker on this album, especially when the cymbals are hit fairly hard as opposed to tapped politely. I'm unsure if these specific cymbals are supposed to sound darker or brighter, but the tiny sonic difference is one way to differentiate between the 866 and other components. I can say for certain that the sound is truly terrific, never harsh, and extremely controlled like all other Boulder amplifiers I've heard in the past. No speakers or headphones are going to control a Boulder amplifier, that's for sure.
In October 2020, Jewel released a deluxe version of her debut album Pieces of You. My favorite track on the album is the radio edit of Foolish Games. I usually hate radio edits because they remove the good parts in an effort to make a track more palatable for a wider audience, but this version of the Foolish Games is really good. The opening piano and strings on this track are night and day better than the original, and all of it can be heard through the Boulder 866 Integrated / RAAL-requisite SR1a combination. Listening to this version through the Boulder 866 is like listening to a completely different version of Jewel. Her vocals are better and several more instruments can be heard in the background, with air around them. The listener is also able to pinpoint the location of the instruments in the soundstage, while listening through headphones. It's quite an enjoyable experience and an incredible way to listen to old tracks again for the first time.
I recently listened to Rick Rubin describe his experience producing Tom Petty's Wildflowers album, and was inspired to listen to the new version fo the album called Wildflowers & All The Rest 9Deluxe Edition). I'd forgotten how much I liked this album, especially the track named Honey Bee. It's an album track for sure, but it's one to which I can't stop listening. Through the Boulder 866 / SR1a combination the electric guitar sounds appropriately dirty, grungy and full of fantastic distortion. As both Tom petty and Mike Campbell start and stop / re-enter the track, the little noises before hitting the strings are all audible and bring the listen that much closer to being in the studio. For a recording that I never considered HiFI, I sure enjoyed all that's captured on it and reproduced through this Boulder amp. In fact, Petty's voice at the very start of the track, "All right here we go ..." Sounds so real it's like my headphones are plugged into the soundboard of the recording studio rather than the outputs of the Boulder 866 Integrated. This is what high end audio is all about to me. Bringing me one step, or two steps closer to the real thing.
My quest to take the RAAL-requisite SR1a headphones to the next level is off to a fantastic start with the Boulder 866 Integrated amplifier. I selected this unit because it has all the features I need and it's manufacturers and supported by one of the best blue chip companies in all of high end audio. The analog and digital version certainly isn't inexpensive at $14,450, but it's a game-set-match component, just add speakers. The 866 Integrated looks really nice on my desk sitting next to my iMac and my headphone stand. The metal chassis is 100% Boulder, making it impossible to misidentify this amp as that from another company. The fit and finish are second to none. When it comes to sound quality, the main reason we are all into this wonderful hobby, the 866 Integrated is fantastic.
I wrote at the start of this review that an amp must be fantastic or else I'd hear its flaws through the SR1a headphones. The Boulder 866 delivers the goods flawlessly at all volume levels. I played everything from test tracks (not really fun, but necessary for evaluation) to tracks that grip me emotionally, and the 866 handle them all with ease. Reproducing incredibly wide dynamic range on bombastic symphonic pieces and the very fine details in Jewel Kilcher's voice that bring out the emotion of an 18 year old busker from Homer, Alaska, the Boulder 866 is an all-in-one that can do it all.
Community Star Ratings and Reviews
I encourage those who have experience with the Boulder 866 Integrated to leave a star rating and quick review on our new Polestar platform.
- Boulder Amps 866 Integrated Analog + Digital ($14,450) ($12,250 Analog only version)
- Boulder 866 Integrated Product Page
- Boulder 866 Owner's Manual (Analog Only)
- Boulder 866 Integrated Owner's Manual (Analog + Digital)
- Boulder 866 Integrated Literature
- Boulder 866 Integrated Quick Start Guide
- Boulder 866 Integrated Dimensions
- Boulder 866 Integrated Remote Guide
- Source: QNAP TVS-872XT, Aurender W20SE, CAPS 20
- DAC: EMM Labs DV2, Berkeley Audio Design Alpha DAC RS3, Schiit Audio Yggdrasil
- D-to-D Converter: Sonore Signature Rendu SE (optical), APL HiFi DNP-SR, CAPS 20.1, Berkeley Audio Design Alpha USB
- Amplifiers: Constellation Audio Mono 1.0 / Monoblock Power Amplifiers, Constellation Audio Inspiration Integrated, Parasound HINT 6
- Preamplifier: Constellation Audio PreAmp 1.0
- Loudspeakers: Wilson Audio Alexia Series 2
- Digital Signal Processing: Accurate Sound, HQPlayer
- Remote Control Software: Roon Remote, JRemote, Aurender Conductor
- Remote Control Hardware: iPad Pro
- Playback Software: Roon, JRiver,
- Network Attached Storage (NAS): QNAP TVS-872XT
- Audio Cables: Transparent Audio Reference Interconnects (XLR & RCA), Transparent Audio Reference 110-Ohm AES/EBU Digital Link, Transparent Audio Reference Speaker Cables, Gotham GAC-4/1 ultraPro Balanced XLR Audio Cable (40')
- USB Cables: Transparent Audio Premium USB Cable
- Power Cables: Transparent Audio Reference Power Cables
- Power Isolation: one 4kVA and one 5 kVA 512 Engineering Symmetrical Power Source
- Ethernet Cables: Transparent Audio High Performance Ethernet Cables
- Fiber optic Cables: Single Mode OS1-9/125um (LC to LC)
- Acoustic Room Treatments: Vicoustic Diffusion and Absorption, ATS Acoustics Bass Traps
- Network: Ubiquiti UniFi Switch 24, Ubiquiti UniFi Switch 8-150W x2, Ubiquiti UniFi Switch 16 XG, Ubiquiti UniFi Security Gateway Pro 4, Ubiquiti UniFi AP HD x2, UniFi FlexHD AP, Ubiquiti FC-SM-300 Fiber Optic Cable x2, UF-SM-1G-S Fiber Optic Modules x6, Commercial Grade Fiber Optic Patch Cables, Calix 716GE-I Optical Network Terminal, CenturyLink 1 Gbps download / upload
This graph shows the frequency response of my room before (top) and after (bottom) tuning by Mitch Barnett of Accurate Sound. The standard used for this curve is EBU 3276. This tuning can be used with Roon, JRiver, and other apps that accept convolution filters. When evaluating equipment I use my system with and without this tuning engaged. The signal processing takes place in the digital domain before the audio reaches the DAC, thus enabling me to evaluate the components under review without anything changing the signal further downstream.