Mixed Marriage

Can a retro tube-based amplifier live happily ever after with the Apple iPod?

4 min read

Apple's iPod reeks of modernity. Its combination of sleek industrial design, capacious storage, and a clever user interface is state of the art. So why would anyone think to mate the iPod with a retrogressive stationary audio component that is based on vacuum tubes?

After auditioning the N and S Valveworks iPod amplifier for more than a month, I'm not sure I'm any closer to an answer than when it arrived. The amplifier, made by N and S, in Saitama, Japan, is as oddly conceived a product as I've ever encountered in more than 20 years of audio reviewing. But it's kind of fun, and in its own way it is an interesting commentary on some frequently overlooked trends in component audio. The survival of the vacuum tube some 30 years after its abandonment by mainstream manufacturers is one of the great anomalies of consumer electronics. Huge, hot, inefficient, and somewhat dangerous, tubes offer no practical advantages over their solid-state counterparts. But what they do provide is a musically natural distortion spectrum and, for many, a superior listening experience.

Photo: Nicholas Eveleigh

Back to the Future:

20th-century tubes amp up the 21st-century iPod.

Even when pushed hard by demanding musical material, tubes overload gracefully, and although the sound at that point is audibly distorted, it still has a singing tone that is almost impossible to duplicate with solid-state circuits. That's why many recording engineers continue to use vacuum tubes in their studios and most premium musical instrument amplifiers also employ tubes. Within the consumer electronics sphere, hundreds of mostly tiny companies make vacuum tube equipment for residential listening systems as well. N and S is one of those companies. Another such company, PsiberAudio of Singapore, has also announced a tube-based iPod amplifier; its iTube SE15 retails at US $900.

One thing the N and S amp clearly shares with the iPod is an acute sense of style. While most tube amps have an antique look about them, the iPod amp is hip and contemporary, available in iPod white or with a lipstick-red paint job, with the iPod docking cradle right in front above the volume control. Three black, disk-shaped toroidal transformers and four vacuum tubes are artfully arranged across the top, presenting an altogether striking visual statement, especially when the amplifier is operating and the tubes are all aglow.

The ergonomics, however, leave something to be desired. For accommodating RCA connector cables, there's a funky phono jack interface that lets you attach the amplifier to other hi-fi components. You have to remove the interface if you're going to connect an iPod, but since that's not stated in the owner's manual, you might get frustrated trying to use the thing.

The internals are a hybrid of tubes and ICs. Audio ICs are used extensively; only the output stage uses tubes. The manufacturer claims distortion of half a percent--remarkable performance if it's true. Maximum output is only 8 watts, so I assume that the amplifier is running hot--which reduces output but improves the accuracy of reproduction. I make this conclusion based on the fact that conventional two-tube circuits using identical tubes are good for 20 to 30 W.

The survival of the vacuum tube some 30 years after its abandonment by mainstream manufacturers is one of the great anomalies of consumer electronics

The large toroidal transformers, used for both the power supply and the output stage, are decidedly unusual in a tube component. The huge majority of tube amps use E-core transformers (shaped like the letter E, instead of donut-shaped toroids) for both the power and output transformers. (Output transformers are used in most tube amps to couple the high-impedance tubes with a low-impedance speaker load.)

Toroidal transformers are more efficient than E-core types but are difficult to wind. Since most output transformers have complex windings that are hard enough to make using a straight core, manufacturers have tended to avoid the toroids. There are a lot of arcane technical arguments for and against the different configurations; from my perspective, the way the windings are interwoven on the core is more important than the basic design.

Before trying the amplifier with an iPod, I connected the amp to a Luxman DU-10 multiformat disc player and Precide hybrid ribbon speakers to establish a performance baseline. The sound of the amp with high-quality superaudio compact disc (SACD) material is wonderful. It is at once sweet and musically natural, comparing favorably with much more expensive products in perceived accuracy, although it lacks the power for reproducing popular music over inefficient speakers. Some of the selections I tried included Manitas de Plata's Guitarra Flamenco, Beethoven piano concertos, and Willie Nelson's album Stardust, all musically natural recordings originally done in analog.

Sadly, playback from iPod recordings was uniformly disappointing, including both tracks ripped from CDs and downloads from Apple's iTunes service. A particularly interesting comparison was provided by a download of Nelson's version of the song "Blue Skies," which appears on his greatest hits album on iTunes and also on the SACD version of >Stardust. The difference was shocking. The iTunes version lacks highs, clarity, and convincing stereo reproduction. The discrepancy is on the order of that between AM and FM radio.

The fault does not really lie in the N and S amplifier. Music from the iPod is still sweet and musical, but it does not provide a lot of realism or reveal the details of the performance, simply because the compressed audio formats used with the iPod and other portable digital players do not reproduce those features.

The iPod amp makes an interesting conversation piece, and it provides superior audio reproduction with good source material, as long as you have efficient speakers and do not demand lease-breaking playback levels. But it can't make MP3s into something they're not--a true high-fidelity medium.

The iPod amp is being sold as a partially assembled kit for approximately $900. The kit does not include the transformers, which are available for about US $300 each from Plitron Manufacturing Inc., in Toronto. For more information, contact N and S Valveworks at fwt34641@yahoo.co.jp .

About the Author

Daniel Sweeney is an analyst in electronics-communication and energy technologies. He is a veteran writer for audio publications and is currently preparing a market study on audio semiconductors.

This article is for IEEE members only. Join IEEE to access our full archive.

Join the world’s largest professional organization devoted to engineering and applied sciences and get access to all of Spectrum’s articles, podcasts, and special reports. Learn more →

If you're already an IEEE member, please sign in to continue reading.

Membership includes:

  • Get unlimited access to IEEE Spectrum content
  • Follow your favorite topics to create a personalized feed of IEEE Spectrum content
  • Save Spectrum articles to read later
  • Network with other technology professionals
  • Establish a professional profile
  • Create a group to share and collaborate on projects
  • Discover IEEE events and activities
  • Join and participate in discussions