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This is the 24th in a series of reviews dedicated to the concept of 32Ohm Audio as embodied by the store of that name in downtown Portland/Oregon and described here - Ed.

Srajan Ebaen
Financial Interests: click here
Source: Ancient Audio Lektor Prime, Apple iMac 1TB with AIFF files up to 24/192, Weiss DAC2, iPod Classic 160GB, Sieben Technology dock, Onkyo NS-D1 digital-direct dock
Preamps: Esoteric C-03, ModWright DM 36.5, Bent Audio Tap X
Amplifiers: FirstWatt F5 & J2, ModWright KWA-100 SE, Trafomatic Audio Kaivalya, Octave Audio MRE-130 with SSB, Yamamoto A-09S
Speakers: ASI Tango R, Zu Essence, Boenicke SLS
Headphones: ALO Audio recabled Audez'e LCD-2, Sennheiser HD800, beyerdynamic T1 and AKG K-702; stock audio-technica W5000; stock Grado PS-1000; HifiMan HE5LE with optional silver wiring and grill mod; Hifi Man HE-6 [on review]
Headphone amps: Trafomatic Audio Head One; Woo Audio Model 5; Burson Audio HA-160; Meier Audio Corda Concerto, Antelope Audio Zodiac+ [on review]
Cables: Complete loom of ASI Liveline, Furutech GT2 and WireWorld Starlight USB A-to-mini-B cables [on loan], LaCie and Entreq Firewire 800 cables, Entreq USB cable, Black Cat Cable Veloce S/PDIF cable [on loan]
Stands: 2 x ASI HeartSong 3-tier, 2 x ASI HeartSong amp stand
Powerline conditioning: 1 x Walker Audio Velocitor S, 1 x Furutech RTP-6
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls, suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without the usual nearby back wall.
Review Component Retail: $1.100 / €980
Having been Realsization-award enthused about their $699 HA160 headphone amp [shown below], team Burson's assertion that after 18 months of hard work they now had something even better piqued my curiosity. The new 3-for-1 HA-160D (Series 160 Headphone Amp with DAC) adds converter and preamp functionality with three analog and two digital inputs—USB and S/PDIF—plus one set of pre-outs. As is company mantra, IC opamps and low-cost 3-pin voltage regulators are left to the devil and his minions. The men from Oz champion fully discrete solutions. Here those include five purpose-built low-noise voltage regulators and fully discrete I/V conversion and analog outputs. Audiophile parts in general are from Elna, Wima, Dale and Philips.

A classic BurrBrown PCM1793 24-bit chip handles conversion. It is fed from a constant current source and passes through Burson's independently powered discrete op amp during current-to-voltage conversion [below center] to guarantee a high slew rate and fast recovery time. From there it hits a fully discrete class A transistor output stage. The volume control is a Burson-built 24-step attenuator with <0.1% metal film resistors in the signal path. It's been reportedly improved over the version in the earlier HA160 whose step spacing with higher output sources I'd criticized. The 6mm aluminum casing once again turns into one monolithic heat sink to support class A operation without the usual finned jobs. This casing clearly contributes to the 265 x 259 x 80mm silver-anodized enclosure's weight of 7kg. Other contributors are two power transformers rather than just one with split secondaries. One tranny is for the DAC, the other for the output stage. This division of labor into digital and analog supplies is said to maximally isolate the critical converter stage from any load behavior on the outputs.

Specs include bandwidth from 5Hz (-0.3dB) to 35kHz (-1dB) with a S/N ratio of better than 98dB at zero circuit gain. THD is less than 0.001% into 6mW/300 ohms. Input impedance is 47K, output power 650mW into 300 ohms, 800 into 60. The output impedance of the line out is 60 ohms, headphones see 5 ohms. Power dissipation is 25 watts. There are two headphone outputs marked 'H' and 'L' for high and low gain. My 600- and 400-ohm beyerdynamic T1 and Sennheiser HD800 headphones would probably plug into the right socket; my 50-ohm Audez'e LCD-2 and particularly the two low-efficiency Hifi Man planars into the left (the gain differential between H and L ports is about 50% as per Burson).

Conceptually the HA160D is ultra modern. iPod & Co. have made headphone listening more popular than ever. Interest in file playback means that even computer-phobic audiophiles need an interface aka USB DAC (Firewire is another option). A headphone amp with USB DAC in a tank enclosure with a fair price and ultra boutique pretensions hits a lot of markers. Adding pre-outs merely squares the circle to eliminate one more extra box. So far so good. Very contemporary.

Attentive observers now might arch a brow. Team Burson thus far has been a purely analogue outfit. In that sector they've made a name as no-nonsense designers who supply more than one established maker and modifier with their discrete buffer and opamp modules. (Their blog contains some actual user feedback on this.) Reading up on the HA160D web page, one notices a focus on Burson's comfort zone. Among other items, that becomes the I/V conversion stage where they could pull rank on the usual chipped op amp and plug in their own discrete module. Meanwhile one learns zip on the jitter-critical USB implementation, clocking schemes, data density compatibility and such. Digital is given short shrift.

This implies not that Burson didn't give it very good thought. In fact, the copper-colored cage shielding the USB transceiver board [lower right corner in above photo] suggests great deliberation not to broadcast details of its implementation. Lack of published information simply creates doubt as to what these folks can bring to the digital table. For very little money we have proven experts like Kevin Halverson of High Resolution Technologies and Marco Manunta of M2Tech with their Streamer II+ and hiFace devices respectively. At higher prices one might name John Stronczer of Bel Canto, Gordon Rankin of Wavelength, Igor Levin of Antelope Audio and many more. If Burson's digital implementation—particularly the en-vogue USB—is anything special, why aren't they... you know, bragging about it just a bit as they already do with their all-discrete I/V implementation? The latter's descriptions claim that most makers underestimate this stage as do most shoppers; that all get unnecessarily embroiled in the 32-bit/384kHz number's war, the obligatory geek specs of digital chips, oversampling rate, async transfer, apodizing filters, field-programmable gate arrays and such. Not Burson of course. But... if their new $1.199 HA-160D is really an improved $699 HA-160, what exactly do the extra $400 buy besides the obvious (more sockets and input switching relays)? Wouldn't prospective buyers consider this to be on a very much need-to-know basis?