|All In Your Head
November 2007Citypulse Audio EF3.01 Headphone Amplifier
by S. Andrea Sundaram
If you desire to hear every minute detail on a recording, there is no better way to do so than by placing transducers mere centimeters from your ears or, in some cases, into your ear canals. Amongst audiophiles, there exists a community of dedicated headphone listeners who will spend thousands of dollars on dedicated headphone amplifiers -- capable of producing only very little power, but with vanishingly low distortion and self-noise well beyond what is possible with a conventional power amplifier. There are a great many more audiophiles who listen through headphones on a much-less-frequent basis, yet still demand great sound. Many of us in this latter group cannot justify to ourselves, or perhaps our significant others, thousands of dollars for a component we don't use every day. On the other hand, we cannot content ourselves with the afterthoughts that are the headphone outputs built into other products, if those outputs exist at all.
Fortunately, a number of companies are now marketing moderately priced headphone amplifiers with a level of sonic sophistication that, while not matching that of their much more expensive cousins, can give a satisfying listening experience. One such offering is the EF3.01 from Citypulse Audio, a Chinese company whose products are distributed in the US by Nat Distribution. Besides the EF3.01 headphone amplifier, Citypulse Audio's other products include an integrated amplifier and two digital-to-analog converters -- one that supports USB. The Citypulse brand has only been in existence since 2005, but the company founders come with nearly 50 years of combined experience in the audio industry.
The EF3.01 ($629 USD) measures 9 7/8"W x 2 1/2"H x 11"D and weighs 10 pounds. Some of that weight doubtless comes from the very solid chassis, but another large part comes from the two toroidal transformers that power the amplification circuitry. On the front of the EF3.01 are a large toggle switch -- which looks like something that came off the space shuttle -- for power, a single 1/4" headphone jack, and a volume knob. Also on the front are a power indicator and an IR receiver for the remote control. Although a headphone amp is often not far enough out of reach to require a remote, the EF3.01 can also be used as a single-source preamplifier, making remote volume a welcome feature. On the back are two sets of high-quality, chassis-mounted, RCA jacks -- one for source input and the other for preamp output. Power comes in via a standard IEC connection, making power-cord upgrades possible.
The EF3.01 is dual-mono in design, with a class-A output stage. It has a quoted frequency response of 10Hz-60kHz with no level given for maximum output. Being a solid-state design, the EF3.01 is capable of driving headphones with impedance from 32 to 600 ohms, which covers the vast majority of full-size cans. Input and preamp-output impedances are both 100k ohms, which should work well with most ancillary equipment. The signal-to-noise ratio is quoted as a respectable 102dB, and distortion is a modest 0.015% (no level given). One specification that I like to see on headphone amps but seldom do is self-noise -- the noise the amp produces when no signal is present, usually given in milivolts. Lamentably, Citypulse Audio does not furnish this specification for the EF3.01.
The EF3.01 does not look particularly elegant or expensive, but there is nothing cheap about its appearance either. The only thing that separates it from being a square box are the slightly curved sides of the faceplate and chassis. While I have no real complaints about the looks, I do have some minor gripes about the feel of the EF3.01. The volume knob is set out from the faceplate a good bit, but the actual part that turns is somewhat shallow. The knob, at least on the review sample, did not turn smoothly, seeming to catch in a few places along its course. When turning it, I could hear a scratchy mechanical sound, but there was no static through the headphones, as can happen with some other volume implementations. The remote is all metal, but the buttons were a little loose and rattly. None of these complaints about the Citypulse is serious, but I do expect better at this price.
Normally, there is very little to do in setting up a headphone amplifier -- connect it to your source, give it power, and plug in your headphones. I found an appropriate place on my equipment rack and plugged the EF3.01 in. The power cord supplied with the unit was abnormally short, so I used one of similar quality that I had lying about. My previous integrated amplifier had a mechanical source-selection knob that would route the selected signal to the record-out jacks even when the amplifier was powered down. Alas, the relay-switching of my current integrated does not allow for such a convenient way of connecting a headphone amplifier to all sources. I had to unplug whichever source I wanted to hear from the integrated and connect it to the EF3.01.
From my Trigon Vanguard 2 phono-stage, interconnects were JPS Superconductors, while from my Ayre C-5xe universal player it was QED Silver Spiral. I used the EF3.01 with two different pairs of headphones -- the ubiquitous Sennheiser HD 600s and my preferred Ultrasone PROline 2500s. Not only do these two headphones have different sonic signatures, but they are also electrically quite different. The HD 600s having a nominal impedance of 600 ohms to the Ultrasones' 40 ohms. An amplifier that is electrically compatible with both of these designs should be capable of driving almost any headphone available.
Perhaps to increase its usefulness as a preamp, the EF3.01 has quite a lot of gain. Whether high gain is good or bad in a headphone amplifier depends a lot on the listener. If you find that headphone outputs of various devices cannot deliver the sound-pressure levels that satisfy you, then you should give the Citypulse headphone amp a try. It has the ability to make headphones play at levels equivalent to the speakers typically found on notebook computers. (Never try a headphone amp at full volume with the headphones on your head, though, or you will almost certainly damage your hearing.)
The downside of having so much gain is that the volume control is only usable over a very limited range. The problem of excessive gain is compounded by the sensitivity of the EF3.01 being only 1.0V-- half the level of a typical CD player output. On most discs, I found that a 30-degree rotation of the volume knob took me from silence to the edge of my tolerance of loudness, even for short periods. While there is nothing unusual about the setup I used, listeners with less efficient headphones, lower-output sources, or those who just prefer listening at higher levels will be able to have finer control over their listening levels with the EF3.01.
Though I had a few complaints about the experience of using the EF3.01, I had fewer about the sound. For me, the first test of a headphone amplifier is whether it makes any noise in the absence of a signal. Headphone listening can be a much more intimate experience than listening to speakers. I find that in the softest passages of a symphony, or in the silence after a track, the presence of any hiss or hum can shatter the world that good music creates. Through the Citypulse EF3.01, I heard a very slight hum and only appreciable hiss with the volume all of the way up. In what I discovered to be the usable volume range, the hiss was not noticeable. I have heard headphone amplifiers that are truly noise free, but I have also heard many that cost more than the EF3.01 and are far noisier, so the Citypulse passes the self-noise test.
For those who think that headphones can't deliver bass, they need only connect their favorite pair of cans to the EF3.01 for an enlightening experience. With it, the Sennheiser HD 600s exhibited reasonable depth and weightiness. The plucked bass on the Andrea Pozza Trio's Sweet Lorraine [Venus TKJV-19154] was taut and bouncy, though still a little reduced in volume than I might expect when listening through full-range speakers. When I substituted the Ultrasone 'phones for the Sennheisers, the quantity of bass increased dramatically. I heard deeper extension and far more power through the PROline 2500s than I had through the HD 600s. The difference was so vast, it seemed as though someone had come along and turned up a bass tone control.
This added weight could certainly appeal to many listeners, but it came at the expense of some definition. The timpani strokes near the beginning of Tchaikovsky's Violin Concerto, as played by Julia Fischer and the Russian National Orchestra on the SACD of the same name [PentaTone 5186 095], were clearly delineated when listening through the HD 600s. Through the Ultrasones, they gained both weight and depth, but blended into each other. Through the Sennheisers, in the same piece I could clearly hear the difference between the pizzicato arpeggiated figures in the low strings and the subsequent bowed figures. Through the Ultrasones, the attack was still different, but the decay of the pizzicato notes was very similar to the short sustain of the bowed notes. While the EF3.01 could coax a greater quantity of bass out of the Ultrasones than out of the Sennheisers, it did not have the same control over that bass. Other headphones may produce a different balance of power and articulation, but with these two choices I found the bass frequencies of the EF3.01 much more to my liking with the HD 600s.
I also found the treble range of the Citypulse EF3.01 to be a more synergistic match with the HD 600s than with my preferred PROline 2500s. On the same Tchaikovsky disc, the cadenza at the end of the first movement offers some beautiful high notes against an empty background. Through the Sennheisers, the EF3.01 reached delicately into the upper frequencies, fading into nothingness. Through the Ultrasones, I heard more of the harmonic texture of these notes, but the overall impression was a bit rougher around the edges. Just as with the low frequencies, I concluded that the EF3.01 had adequate extension, but it took the right partnering equipment to show off that extension properly.
Some say that if the midrange is done right, then nothing else matters. The Citypulse EF3.01 has a clean, solid, midrange that works with all sorts of music. Whether jazz or classical, vocal or instrumental, the EF3.01 managed a neutral tonal balance. While I might prefer a little added tube warmth in this range, I can't call the EF3.01 lean. Each instrument sounded, more or less, as it does in real life, with no bloated violins or razor-thin cellos. Voices were also rendered in proper tonal proportions. On the title track of The Girl in the Other Room [Verve B000182602], Diana Krall's voice had the right mix of huskiness and breathiness. The EF3.01 clearly brought out that Krall's voice has depth but is not supported from the diaphragm. That distinction is one that can be easily lost by a component that does not have an even response over the middle frequencies.
Soundstaging presents an interesting problem for headphones. The only designs that I've heard construct a convincing soundstage are those from Ultrasone. Even the PROline 2500s need a good headphone amplifier to perform their out-of-the-head trick, and they managed it with the EF3.01. With other amplifiers, I've heard them throw a stage that is a little wider and a little deeper, but the results here were still very good. I could clearly hear the placement of instruments with respect to one another, and their proportions were believable. When voices moved across the stage on Wagner's Der fliegende Holländer [EMI 674052B], I could hear them moving in space, not merely panning from one channel to the other.
There is no shortage of choices in headphone amplifiers around the Citypulse EF3.01's price. My reference for quite some time was the Musical Fidelity X-CAN v3, which currently retails for $499 -- not out of line with the cost of the EF3.01. Even before sitting down to do any listening, there are some clear differences between these two components. The X-CAN v3 is a somewhat smaller package than the EF3.01. Primarily, the difference in size and weight is due to the X-CAN's wall-wart power supply, as opposed to the internal transformers of the EF3.01. The Musical Fidelity unit looks to be the more expensive of the two, with its polished faceplate and beveled edges. The volume knob is also an ergonomic wonder -- turning it is pure luxury. These two amplifiers are also different electrically. The Musical Fidelity employs tubes, though it is not solely a tubed circuit, while the Citypulse is entirely solid state. Looking at the back of each unit, you will find both inputs and outputs, but in the case of the X-CAN v3, the outputs are only a pass-through. The X-CAN v3 cannot be used as a preamplifier.
These two headphone amplifiers also sound quite different. The Musical Fidelity amp is fairly quiet in the absence of a signal, but the Citypulse is noticeably quieter. Both amplifiers can play louder than I care to listen, but the EF3.01 seems to have an endless capacity for volume. I wouldn't classify the X-CAN v3 as wispy and ethereal, but the EF3.01 has a far more solid and robust sound. The Musical Fidelity amp presents music, whereas the Citypulse does more to drive it forward.
In the bass frequencies, the Citypulse is the clear winner, having significantly more extension, weight, and impact. The bass response of the Musical Fidelity amp is sufficient for most types of music, but it won't impress bass fanatics. At the other frequency extreme, the X-CAN v3 is more open and airy than the EF3.01 -- painting high notes, and their harmonics, with a lighter brush stroke, thereby revealing more of their subtle structure. The midranges of both amplifiers are well rendered, but in different ways. The Musical Fidelity endows instruments and voices with more warmth, the Citypulse with more physicality. I find the Citypulse to be the more neutral performer, but the slight colorations of the Musical Fidelity add a little extra beauty.
In a crowded marketplace, it can be difficult for a product from a relatively new company to stand out. The Citypulse EF3.01 is a competently designed product with reasonable build quality. Given the right headphones -- seemingly those with highish impedance -- it is capable of delivering an all-around honest and enjoyable performance. For those listeners who want a little extra power, particularly in the bass, the Citypulse EF3.01 can deliver better than most headphone amplifiers at its price point.
As with any piece of audio equipment, the final arbiter of its quality and value is you, and determining this is especially easy with a headphone amp. So grab your favorite pair of headphones -- especially if they are Sennheiser HD 600s -- and give the EF3.01 a listen. I was impressed, and I bet you will be too.
...S. Andrea Sundaram
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