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72 IEEE Spectrum | June 2005 | NA

RESOURCES

MIXEDMARRIAGECan a retro tube-based

amplifier live happily ever

after with the Apple iPod?BY DANIEL SWEENEY

Apple’s iPod reeks of modernity. Itscombination of sleek industrialdesign, capacious storage, and aclever user interface is state of theart. So why would anyone think tomate the iPod with a retrogressivestationary audio component that isbased on vacuum tubes?

After auditioning the N&SValveworks iPod amplifier for morethan a month, I’m not sure I’m any

closer to an answer than when it arrived.The amplifier, made by N&S, in Saitama,Japan, is as oddly conceived a productas I’ve ever encountered in more than20 years of audio reviewing. But it’s kindof fun, and in its own way it is an inter-esting commentary on some frequentlyoverlooked trends in component audio.The survival of the vacuum tube some30 years after its abandonment by main-stream manufacturers is one of the greatanomalies of consumer electronics. Huge,hot, inefficient, and somewhat danger-ous, tubes offer no practical advantagesover their solid-state counterparts. But

what they do provide is a musicallynatural distortion spectrum and, formany, a superior listening experience.

Even when pushed hard by demand-ing musical material, tubes overloadgracefully, and although the sound at thatpoint is audibly distorted, it still has asinging tone that is almost impossibleto duplicate with solid-state circuits.That’s why many recording engineerscontinue to use vacuum tubes in theirstudios and most premium musicalinstrument amplifiers also employ tubes.Within the consumer electronics sphere,hundreds of mostly tiny companies makevacuum tube equipment for residentiallistening systems as well. N&S is one ofthose companies. Another such com-pany, PsiberAudio of Singapore, has alsoannounced a tube-based iPod amplifier;its iTube SE15 retails at US $900.

ONE THING THE N&S AMP CLEARLY

shares with the iPod is an acute sense ofstyle. While most tube amps have anantique look about them, the iPod ampis hip and contemporary, available in iPodwhite or with a lipstick-red paint job,with the iPod docking cradle right in frontabove the volume control. Three black,disk-shaped toroidal transformers andfour vacuum tubes are artfully arrangedacross the top, presenting an altogetherstriking visual statement, especiallywhen the amplifier is operating and thetubes are all aglow.

BACK TO THE FUTURE:

20th-century tubes amp up

the 21st-century iPod.

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June 2005 | IEEE Spectrum | NA 73

The ergonomics, however, leave some-thing to be desired. For accommodatingRCA connector cables, there’s a funkyphono jack interface that lets you attachthe amplifier to other hi-fi components.You have to remove the interface if you’regoing to connect an iPod, but since that’snot stated in the owner’s manual, youmight get frustrated trying to use the thing.

The internals are a hybrid of tubes andICs. Audio ICs are used extensively; onlythe output stage uses tubes. The manu-facturer claims distortion of half a per-cent—remarkable performance if it’s true.Maximum output is only 8 watts, so Iassume that the amplifier is runninghot—which reduces output but improvesthe accuracy of reproduction. I make thisconclusion based on the fact that con-ventional two-tube circuits using iden-tical tubes are good for 20 to 30 W.

The large toroidal transformers, usedfor both the power supply and the outputstage, are decidedly unusual in a tubecomponent. The huge majority of tubeamps use E-core trans-formers (shaped likethe letter E, instead ofdonut-shaped toroids)for both the power andoutput transformers.(Output transformersare used in most tubeamps to couple the high-impedance tubeswith a low-impedance speaker load.)

Toroidal transformers are more effi-cient than E-core types but are difficultto wind. Since most output transformershave complex windings that are hardenough to make using a straight core, manu-facturers have tended to avoid the toroids.There are a lot of arcane technical argu-ments for and against the different con-figurations; from my perspective, the waythe windings are interwoven on the coreis more important than the basic design.

BEFORE TRYING the amplifier with aniPod, I connected the amp to a LuxmanDU-10 multiformat disc player and Pre-cide hybrid ribbon speakers to establisha performance baseline. The sound of theamp with high-quality superaudio com-pact disc (SACD) material is wonderful.It is at once sweet and musically natu-ral, comparing favorably with much moreexpensive products in perceived accu-racy, although it lacks the power forreproducing popular music over ineffi-

cient speakers. Some of the selectionsItried included Manitas de Plata’s GuitarraFlamenco, Beethoven piano concertos,and Willie Nelson’s album Stardust, allmusically natural recordings originallydone in analog.

Sadly, playback from iPod recordingswas uniformly disappointing, includingboth tracks ripped from CDs and down-loads from Apple’s iTunes service. A par-ticularly interesting comparison wasprovided by a download of Nelson’s ver-sion of the song “Blue Skies,” whichappears on his greatest hits album oniTunes and also on the SACD version ofStardust. The difference was shocking.The iTunes version lacks highs, clarity,and convincing stereo reproduction. Thediscrepancy is on the order of that betweenAM and FM radio.

The fault does not really lie in the N&Samplifier. Music from the iPod is stillsweet and musical, but it does not pro-vide a lot of realism or reveal the detailsof the performance, simply because the

compressed audio formats used with theiPod and other portable digital players donot reproduce those features.

The iPod amp makes an interestingconversation piece, and it provides supe-rior audio reproduction with good sourcematerial, as long as you have efficientspeakers and do not demand lease-breaking playback levels. But it can’t makeMP3s into something they’re not—a true high-fidelity medium.

The iPod amp is being sold as a par-tially assembled kit for approximately$900. The kit does not include the trans-formers, which are available for aboutUS $300 each from Plitron Manufac-turing Inc., in Toronto. For more infor-mation, contact N&S Valveworks atfwt34641@yahoo.co.jp. �

DANIEL SWEENEY is an analyst inelectronics-communication and energy technologies. Heis a veteran writer for audio publications andis currently preparing a market study onaudio semiconductors.

THE SURVIVAL OF THE VACUUM TUBE

some 30 YEARS after its abandonment by

mainstream manufacturers is one of the

great anomalies of consumer electronics