July 2005

The Nearfield
A Straight Wire With Gain
Article By Steven Stone

  "A straight wire with gain." That was electronics designer Stewart Hegeman's definition of the perfect amplifier. Fifty years after he issued his terse description electronics manufacturers are still striving to achieve his elusive goal. This month we'll look at two amplifiers that couldn't be more different. One weighs under a pound and costs less than $50 while the other weighs close to 42 lbs and costs nearly $3000. Surprisingly, in one situation I'd rather have the $50 amp. For when, where, and why, read on.

The Sonic Impact T-amp
Sonic Impact makes several products aimed at the portable lifestyle audio market, including compact speakers, backpacks with built-in speakers, and the Sonic T-amp. This tiny amplifier was designed primarily to drive portable high-efficiency speakers. I first discovered it via eBay, where several resellers offer T-amps for prices varying from $25 to $50. Since I love a bargain as much, if not more, than the next audiophile, I bought a T-amp on eBay for $41 including shipping.

On paper the T-amp doesn't look like much.  It puts out 9 watts into a 4 ohm load, generating only .04% THD. That's OK. But when pushed to 15 watts, its distortion figure balloons up to a whopping 10% THD. That's bad.

In person the T-amp looks like just another piece of cheap portable electronics. Its silver colored plastic exterior reminds me more of a budget-priced ion generator than any kind of high-end audio product. Its only control consists of a flimsy on/off volume knob with a small red LED above it. The bottom of the T-amp has a battery compartment door for 8 AA batteries. Its rear panel has a mini-stereo input and a 12-volt power connector flanked by a pair of really cheesy spring-loaded speaker wire posts. Forget trying to use spade plugs, banana plugs, X-terminators, or anything more robust than a bit of bare speaker wire. These speaker connectors are simply pitiful.

Given its unprepossessing specifications and physical stature why should the T-amp elicit anything more positive than a polite yawn? Simply because it uses the Tripath TA 2024 amplifier IC chip, which is similar to the device found in Bel Canto's EVO-2 amplifier. But just because the T-amp has a Tripath circuit doesn't make it the same as a Bel Canto any more than a Ford with Firestone tires equals a Ferrari with Firestones. One part does not a whole product make. Ask any amplifier designer about what matters in an amplifier and they'll mention not only the output circuit, but also the power supply, signal path, attenuation devices, physical and electrical isolation, and overall circuit topology.

The Sound and the Fury
Until I actually hooked up the T-amp I was of the opinion I had paid about $31 more for this amplifier than it was actually worth. But within very particular parameters the T-amp can sound far better than many amps that cost substantially more.

First off, any speakers you intend to tether to the T-amp must be hyper efficient. Anything less than 90dB/W/m sensitivity at one watt won't work. Even high efficiency doesn't guarantee sonic success. The T-amp's ideal transducer needs to be not only sensitive, but also capable of performing optimally when supplied with very little current.  Since the most robust outboard 12-volt power supply you can safely attach to the T-amp should produce only 5 Amps, you can't expect the T-amp to put out a great deal current. This lack of current capability means the T-amp won't supply anything more than minimal electronic damping. Once a driver is set in motion, the T-amp doesn't do much to stop its motion.

I tried the T-amp with a variety of small desktop speakers. My most successful pairing resulted when I mated it with the Role Discovery speaker. This 90dB/W/m efficient mini-monitor gave me an inkling into the T-amp's potential. The combination created a very accurate soundstage that had better depth recreation than I've obtained using most solid-state amplifiers, including my reference Accuphase P-300. The T-amp's three-dimensionality almost equaled the Bel Canto EVO-2. The T-amp also achieved a level of harmonic purity that rivaled the Bel Canto, but only when the output level remained low. Although the T-amp's volume knob extends clockwise from 6 o'clock to 5 o'clock, if you turn it up past 10 o'clock the sound degenerates rapidly. Above 12 o'clock the T-amp sounds like a bad '60's vintage transistor radio.

If dynamics or bass are your thing you can forget the T-amp. It simply doesn't have the drive to produce wide dynamic contrasts or successfully control the bass. Even on the hyper-efficient Role speakers its dynamic palette was truncated and the bass below 250 Hz wooly and vague. Although the T-amp's top end has a natural and musical quality, its extreme high frequencies lack air, much like you hear from a stock vintage tube amplifier. But the T-amp does get the midrange right. A lack of noticeable electronic grain makes the T-amp remarkably easy to listen to when not driven past its capabilities.

Even if you try using two T-amps in a dual mono set-up, their lack of adequate current and damping combined with their really awful speaker wire connectors will probably leave you sonically and ergonomically unsatisfied. Given that a vast majority of premium desktop speakers have sensitivities in and around 85 dB at one watt, the T-amp's miniscule power output makes its usefulness severely limited. But there is one particular desktop application where the T-amp can still prove to be invaluable — coupled to older, low-voltage Stax Electrostatic ear-speakers.

About two months ago I purchased a pair of Stax SR-30 ear-speakers with a SRD-4 adapter from an eBay seller for $75. I already had a pair of Stax Lambda Nova Pro's coupled with a Stax SRM-1/Mk-2 driver unit and a pair of older Stax Lambda Pros tethered to a Stax SRM-1 driver unit. I bought the SR-30's because I wanted a smaller, lighter, and cheaper pair of headphones that I could use on-location as well as for desktop listening. Unlike the SRM units, the SRD-4 isn't an amplifier, but merely an adapter that couples the Stax SR-30's to the amplifier of your choice.

The speaker connection cables on the back of the SRD-4 are pitiful little beasties. One afternoon I was looking at the back of the T-amp, with its tiny speaker wire connectors and I thought of the SRD-4. What a perfect match! I immediately hooked the SRD-4 to the T-amp and then ran the output from my Perpetual Technologies P-3A into the T-amp. I put on the Darrell Scott Live in N.C. disc. And presto, high-end nirvana! The T-amp can drive the Stax SR-30's to satisfying SPLs, plus they don't seem to mind its lack of electronic damping since the Stax's hyper-thin membranes already stop and start on a dime.

Does the T-amp/SRD-4/SR-30 combo sound as good as a Stax Lambda Pro Nova attached to the Stax SRM-1/MK-2 combination? No. But the sonic advantage is not as lopsided as you might imagine. Sure the Stax Pro's have more tightly controlled and articulated bass and a more extended high end, but the SR-30's nearly match them in midrange purity, inner detail, and overall musicality. When it comes to portability the T-amp/SRD-4/SR-30 combo has a clear advantage since it weighs less than 1.5 lbs and can be run on batteries. For location monitoring, my Stax Pro's may soon be replaced by this lighter, cheaper, and more flexible rig.

If you own an earlier pair of lower voltage Stax headphones I encourage you to try mating them with a Sonic Impact T-amp. While the end result isn't as compact as the latest generation Stax ear-bud, it still delivers a fully portable monitoring solution for a ridiculously low price.

So there you have it — the Sonic Impact T-amp ranks as a fine electrostatic headphone amplifier, but is extremely limited as a loudspeaker amplifier. And it's cute in a cheesy plastic Jetson's way. Fortunately, the T-amp is also dirt-cheap.

The Accuphase E-213
Turning from the Sonic Impact T-amp to the Accuphase E-213 integrated amplifier is a bit like going from a plastic toy Chevy Nova to a real-life Lexus. When Accuphase's first products arrived in the United States during the mid-70's they were often referred to as "The Japanese McIntosh." In the intervening 30 years Accuphase has developed such a stellar reputation for quality that many audiophiles now call McIntosh "the Korean Accuphase." When it comes to premium-priced fully featured high-end audio gear Accuphase has earned the unique position of having few peers.

Although the E-213 stands as Accuphase's least expensive offering, at $2999 it can hardly be considered budget-priced.  Indeed nothing about the E-213 is cheap, and nowhere will you find any signs that the E-213 was built with an eye toward minimizing its final cost. It shares the same sumptuous exterior as its pricier siblings, as well as a similar circuit topology and ergonomic design. Only its somewhat limited power output of 90 Watts RMS (small by Accuphase standards) and single slot for optional accessory boards separates it from pricier Accuphase products.

Technical specifications for the E-213 promise 115 watts into 4 ohms, 105 watts into 6 ohms and 90 watts into 8 ohms. Total harmonic distortion weighs in at .04% from 20Hz to 20kHz with anything from a 4 to 16 ohm load. The damping factor measures 100 with an 8 ohm load at 50Hz. Frequency response at one watt varies less 0.2dB from 20Hz to 20kHz and less than 3dB between 2 and 150 KHz.  Signal to noise measures 110dB with a high level single ended input, 92dB with a balanced input, and 123dB from the direct to power amplifier input. The E-213's produces 42dB of gain from its high level inputs and 28dB from its power amplifier. Idling the E-213 draws 43 watts, while at full power it draws 230 watts.

The E-213's front panel displays Accuphase's classic cosmetics, with a pair of large VU meters occupying the center of the faceplate, flanked on either side by a pair of large knobs. The left-hand knob selects the input source while the right-hand knob controls volume. Underneath the VU meters are smaller knobs and buttons for turning power on and off, selecting main, remote, or both sets of speakers, direct to amplifier bypass selector, recorder selector, mono or stereo selector, loudness or contour circuit, tone controls bypass selector, treble, bass, balance, mute, and a headphone jack. As is Accuphase's tradition, all the controls are laid out in a nearly symmetrical arrangement.

The back of the E-213 has three sets of single-ended RCA line level inputs, one pair of balanced XLR inputs, a pair of single-ended RCA tape recorder inputs and outputs, one set of direct inputs that bypass the E-213's preamp stage, two pair of heavy-duty five-way binding posts, and a standard IEC AC inlet. On the extreme left side of the E-213's rear panel there's an option board slot that can accept Accuphase's DAC-10 digital input board, AD-9 or AD-10 analog phono input boards, or a Line-9 line-level input board.

As you would expect from a modern integrated amplifier, the E-213 comes equipped with a remote control to select input sources and volume levels. The remote's compact size and miniature stature almost guarantees that it will probably spend much of its time lost, nestled between cushions or buried under desktop detritus. Fortunately all the Accuphase E-123's functions can easily be adjusted from the amplifier's front panel.

For desktop set-up, where a subwoofer is standard, you must use the second set of speaker outputs for the subwoofer since the E-123 has no line-level outputs. If your subwoofer lacks high-level inputs this could present a problem. Older Stax headphone owners with SRD connection boxes will be forced to choose between a subwoofer and their headphones, or putting the Stax box in the middle of the subwoofer signal chain.

A Smooth Operator
For discriminating audiophiles the concept of absolute sonic neutrality ranks as an oxymoron of equal stature to "military intelligence." Even the Accuphase E-213 has a particular sound that differentiates it from a true "straight wire with gain." In the case of the Accuphase this sound could best be described as solid-state suave, slightly darker than neutral, and harmonically rich.

Even with the most inefficient desktop speakers I found the E-213 could produce more than satisfying volume levels without stress. According to the Accuphase's output level meters, the most punishing dynamic peaks used only about 25 watts. On my own live concert recordings, many of which have as much as a 50 dB dynamic range from the quietest passages to the loudest, the E-213 handled the finer details of the dynamics with aplomb. Even when played at rollicking volume levels loud passages never sounded compressed and quiet passages retained their subtlety and micro dynamics.

The E-213 resolves low level musical details almost as well as my reference system of the Monolithic Sound PA-1 passive/active preamp tethered to the Accuphase P-300. By coupling a purist preamp, such as the Monolithic PA-1, to the E-213 and bypassing the Accuphase's preamp section you can improve the E-213's overall performance by several notches. When attached to the Monolithic Sound PA-1 preamp, low-level detail actually surpassed my reference rig. For maximum performance without an outboard preamp it's imperative to leave the E-213's tone controls in bypass mode. Activating the controls places a noticeable veil over not only the E-213's resolving powers, but also its dynamic capabilities.

As you might expect from a solid-state power amplifier, the E-213's lateral focus far exceeds its three dimensional abilities. While not completely two dimensional, the E-213 certainly can't create the kind of realistic fully fleshed out images you can obtain from a top-tier tube amplifier. Still, on phase-coherent recordings you will hear distinct dimensional layers that create a convincing allusion of depth. Unfortunately most pop recordings will sound as flat as low-carb pancakes. But when it comes to lateral focus and pinpoint imaging the E-213 can rival any amplifier on the planet. On my own live concert recording of Brahms' Requiem every chorister's voice had its own unique spot in a lateral plane.

Taken as a harmonic whole the E-213 has a slightly darker than neutral palette. The combination of a sweet top end coupled with a warmish lower midrange and upper bass makes the E-213 sound uncharacteristically musical compared to a conventional solid-state amplifier. While it's high end is neither hooded nor rolled off, the E-213 still has less upper frequency extension than the Accuphase P-300. But the P-300's matter-of-fact harmonic presentation sounds more electronic and mechanical. The E-213's high frequencies more closely resemble the Bel Canto EVO-2, but without the Bel Canto's last bit of air and extension.

An amplifier's transient acuity translates in musical terms to the music's "pace." The E-213 delivers a trifle less speed than both the P-300 and the EVO-2, but never sounds sluggish, only a bit more relaxed and laid back. Its above average damping and current delivery keeps the bass under tight control, which translates into tuneful yet powerful bass response. With both the Thiel PCS and Aerial model 5's I could easily have turned off my subwoofer and lost little in the way of bass impact.

Given the E-213's musical presentation it should come as no surprise that even after an extended all-day listening session this amplifier still sounds as inviting as it did in the morning. When coupled to a superior speaker the E-213 can produce seductively convincing first class sound that can make leaving your desktop more than a little difficult. Although Accuphase makes several far more powerful and substantially more expensive power amplifiers, I suspect all but the most fanatical desktop listener will be deliriously happy with the E-213 at the heart of a very suave and satisfying high-end desktop system.