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Reviewer: Ryan Clarin
Source: Meridian G08, Meridian G07
Amps: Eddie Current EC-01 [this review], PS Audio GCHA [review], Emmeline HR-2, Emmeline II Raptor
Headphones: John Grado RS-1, Joe Grado HP-1000, Sennheiser HD600 with Cardas, Sennheiser HD650 with Equinox, Shure E5
Cables: VH Audio Airsine, BPT L-10 power cord, BPT IC-SL interconnects, Chimera Labs Advantage II interconnects
Power: BPT PPC outfitted with Oyaide Rhodium outlets, Oyaide Rhodium outlet on wall.
Review components retail: $349; $299 for standalone EC/DC impedance converter; $595 for both

The Eddie Current EC-01 is a new offering from Craig Uthus, formerly of Moth Audio. This piece is the result of a collaboration between Eddie Current and the Laconic Company from Latvia, Russia. The EC-01 houses the power supply and circuitry in one compact box of sturdy brushed aluminum. The regulated power supply features a toroidal transformer with a huge bank of highly rated capacitors, allowing the music to be played for about 10 seconds after power is shut off. The signal circuitry utilizes a 6N3P for gain and two 6N6P tubes as output tubes. Apparently, these are NOS Russian military issue, quite rare and not commonly used. My research has also shown that the 6N6P exhibits similar mu and distortion specs to the 5687 tubes but supplies 3 x the current while output impedance remains about 1/3rd that of a 5687. The 5687s have gained popularity in the headphone amp world for their high current output as demonstrated with the Emmeline II Raptor and the SLAM iterations of the SinglePower line. Yet these Russian tubes in the EC-01 appear to offer even more current drive. The Eddie Current EC-01 is a single-ended Class A OTL designed to drive loads between 60 and 600 ohms. The EC-01 is based on the Laconic HA-03B, to which Craig has added a voltage regulator on the 6N3P while upgrading all power supply capacitors. The output stage has no gain and uses its two triodes stacked on top of each other to provide the drive for the headphone load. The voltage gain comes from the third triode and Craig believes that this topology creates "a sonic signature that is close to neutral with the specified load."

Going back to his stint with Moth Audio and past Eddie Current products, all of his creations utilize vacuum tubes. I asked him why he favors tubes. Craig replied that "all active devices have a sonic signature. FETS, MOSFETS, transistors, tubes. To complicate things, the circuit topology that is implemented for any given technology -- tubes, transistors -- also has a sonic signature. The drive capability, source resistance, bandwidth, noise and the type of load -- resistive, reactive -- also affect the sound. In my opinion, the transfer characteristic of the triode vacuum tube is the closest to sounding like music."

When I received the EC-01, I was taken aback by its small stature and plain-as-Jane chassis. However, once I popped the hood to take a peek at the internals, it was clear that Craig and Laconic stress substance over style. A highly rated toroidal transformer appears to be a major influence on the amp's overall weight, with a huge bank of capacitors located underneath. Point-to-point wiring is cleanly routed and the EC-01's layout is very compact and utilizes a two-layer approach similar to the Emmeline II Raptor to enable its small footprint. The tubes each have their own damper to aid with tube life and microphonics. The pictures show what's inside this $350 headphone amp. At least by my accounts, it's a lot. The amp also has two inputs and the fuse is accessible from the back.

Craig burns in the units for 48 hours, which he claims is sufficient since further break-in is unnoticeable by his account. I added another 48 hours and decided to listen from there on out. Right off, I was startled by the amp's dynamic nature and after 3months, I am still smitten with how hard this thing can rock. The EC-01 has a very punchy, fast sound, with great bass drive and extension. Bass was quick and taut and each note is clearly delineated within the musical line. Extension was superb and the actual force of the bass is substantial and hard-hitting without being bloated. I've used the analogy before that bass should be like an upper middleweight boxer - with the muscle and power to knock anyone down while retaining the finesse and agility to glide effortlessly across the ring. The EC-01 can easily hang with some of the heavier-hitting solid-staters I have listened to. Obviously bass on headphones is quite a different experience than one gets from speakers which can pressurize air to be felt over the entire body. Yet I was more than satisfied with the EC-01's bass and even more amazed that it was coming out of a little OTL single-ended triode headphone amp. This thing can kick butt. It had my toe tapping wildly.

Another thing that should be noted is that the amp is dead quiet. With the volume pot turned to max, there is just a tiny hint of hiss that's barely noticeable. I would imagine most listeners would not even hear it. Under normal listening volumes, blackground is clearly evident. There is silence between notes, which I believe to be a big part of the EC-01's punchy, dynamic nature. The ultra-efficient Shure E5's were able to reveal some natural tube hiss but it was so low that the E5s had to dig quite low towards the bottom of the noise floor to pick it up.

With the Sennheiser HD600s, there was some harshness on top, with the presentation a bit forward and a slight edge to the upper midrange. This gave the Senns a Grado-type sound, making guitars sound even more electric and lively but adding just a bit of nasality to some of my favorite female singers. Further burn-in did not appear to smooth it out so I contacted Craig to get his opinion. "Yes, I agree. When I first started working with Laconic, the amplifier had unacceptable background noise. I got that under control but it is a little too fast for headphones like the Senn 600s. This is very subtle and most people can't hear it. Looking closely at the square wave response shows a slight overshoot starting at 10kHz. It is only .5dB above baseline but enough to add an edgy sound to the presentation."

I received one of the very first EC-01s from Craig's initial batch and a couple of things still needed to be ironed out. About a week after receiving the amp, the fuse blew. Craig diagnosed that the fuse value set by the Laconic Company was incorrect for the typical 120V AC used here in the States and quickly dispatched a new 1.5A fast blow fuse. The EC-01 has worked perfectly since. Craig also decided to implement a damper network on the output of all EC-01s to help ameliorate the edgy presentation I detected. According to Craig, "...the damper is the opposite of the series resistance plus inductance of the 600/650 Sennheiser headphones. It basically cancels the phase shift and frequency anomalies when driving a reactive load. It is simply a RC network across the load with the correct values for R and C." Craig also mentioned that "all headphone amps without compensation with relatively high source output resistances like 80 ohms in the case of the EC-01 will exhibit a rise in frequency response as the impedance curve of something like the Senn 650s rises. The 300-ohm and even 200-ohm cans like the Beyers do it too." Craig even sent me two scope traces to show the effect of the RC damper network. Both graphs show the square wave response of the Sennheisers at 10kHz. Anyone who received an EC-01 from the first run can send in the amp for a free upgrade. Future customers have the option of having the damper implemented or not.

Early on within the review process, Craig had also mentioned that he was considering implementing an impedance converter box that would allow users to hook the EC-01 to low-impedance cans like Grados. Operating in single-ended class A operation without an output transformer means the EC-01's 80-ohm output impedance is a mismatch for the Grado's 32-ohm input impedance. Just for kicks, I went ahead and plugged in my Grado RS-1s and HP-1000s anyway. They sounded okay with decent volume but things were a bit strained, lacking in dynamics and focus and the bass was bloated and woolly with very little drive and extension.

However, that was probably due more to the high output impedance of the EC-01 than any lack of inherence drive. The 5687s drive the low-impedance Grados with ample control and the 6N6P purportedly supply thrice the current of the 5687. Craig used to produce the transformer-coupled HD25 with a 6SN7/6AS7 combination that drove Grados very nicely. He had to discontinue it since due to high manufacturing costs and lack of sales. I asked Craig about the use of output transformers in tube designs. "Transformers are the bane of tube amplifier design. Single-ended transformers like the ones used in the older HD25 have the DC voltage the tube needs to see flowing through the transformer. This makes the transformer harder to design, bigger and more expensive. If there is no DC on the transformer primary, it can be smaller and have much better performance at a lower cost. The HD25 had good transformers but since the EC-01 is AC-coupled (meaning there is a DC blocking capacitor), no DC gets to the output and the transformer can be much better. The catch 22 is that the cap/transformer combination, no matter how good the parts, never sounds the same as a good transformer with DC flowing threw it by itself. Specs are one thing, sound is another. Everything is a trade-off."

For his optional impedance down-converter, Craig did have a transformers custom made from Electra-Print to "exhibit perfect square wave response with headphone loading. It has a bandwidth of -.5 dB from 8Hz to 30kHz. It lowers the source out of the EC-01 from 80 ohms to 15 ohms. It increases drive to the Grado RS-1s from 50mW to 750mW. Since there is no DC, the primary can be wound differently. That transformer in your setup has no overshoot or ringing. It is almost a perfect transformer. The HD25 did have a little overshoot and ringing and if you looked at the square wave response, it was pretty ragged around 10kHz. This manifested as a slightly rough high-end response. So comparing the two, the HD25 was punchy and in your face. It played with authority. The EC/DC-equipped EC-01 is very accurate but smooth at the same time."

Craig sent me this fix for the EC-01 in preproduction form [above]. It consisted of an open frame chassis that housed the RC damper network and the transformers. There are two output jacks, one labeled high, the other low. The high output jack has the damper network on it while the custom transformers feed the low output jack. A front panel switch selects between the 2 jacks and a ¼ inch lead out of the back hooks directly to the headphone output of the EC-01. Don't be alarmed by the apparent ghetto nature of what Craig sent me. It was something he simply concocted in order for me to check out the effect of the damper on the EC-01 with high impedance cans as well as the effect of the output transformers. The production EC/DC [below] is contained within a nice chassis with beautiful gold silk-screening. It sports a polarity switch, one ¼ inch input, one ¼ inch output, 1 set of balanced outputs and 2 sets of unbalanced outputs. [In general, one would wish that manufacturers waited until a product was truly finalized rather than using the review process to fine-tune their gear while submitting prototype add-ons to our writers - Ed.]

I listened to the Sennheisers through the damper and enjoyed what I was hearing. The sound remained dynamic, punchy and fast but was smoother and more natural on top. As a tube design, it had all the sonic goods that come from a finely executed tube amp while compromising very little. Tubes simply deliver the goods when it comes to soundstaging where, in my opinion of course, they are superior to solid-state designs. The EC-01 was so adept at capturing spatial and ambient information that it breathed new meaning into the phrase "being in the recording".

As stated in previous reviews, I have a listening preference geared more toward air and ambiance and the EC-01 was more than satisfactory in that regard. While the PS Audio GCHA had great depth and width, the EC-01 not only matched but exceeded its scale while sounding more cohesive and together. Especially SETs are known for their midrange and the EC-01 is a winner. There is the expression that female vocals on a good headphone amp should sound like the signer is sitting on your lap, singing right into your ear. The response can be startling. Females lost their nasal tone present without the damper and sounded like real sexy women who simply demanded your attention. The female voice has the ability to be warm yet resonate upper frequencies. It can be smooth yet have bite, and can also sound forward and intimate while remaining relaxed. The EC-01 made the likes of Ella, Jacintha, Jane Monheit, Alison Kraus, Aimee Mann and Joni Mitchell utterly breathtaking. In regards to soundstage and midrange reproduction, the EC-01 is best described as sounding alive. The stage is big and cohesive and the air around the performers breathes. Instruments are present and immediate without being overtly forward, possessing what I like to call palpable presence. There must be something rather unique about the process of thermionic emission because even though there are plenty of great solid-state designs that can do soundstage and midrange well, it seems that to go that extra mile and break into that area we like to call realism, tubes are the way to go.

In my book of generalizations, headphone listeners fall between two extremes, bassheads and airheads. I'm close to the middle but lean towards the airhead side because space and air get my musical jones burning. My listening preferences lean towards the midrange side of things as well. As a singer and chorus director, accurate timbre within the vocal range is very important to me and I am usually able to compromise other aspects if a component gets the midrange right while portraying an accurate sense of space. That is probably why I gravitate towards and simply enjoy music more from tube amps. It also explains why I am pretty much a dedicated Grado and Sennheiser user. The Grados give me the midrange I need and the Senns the soundstage. I noticed over time that the EC-01 was just a tad hot in the presence region. For some listeners, the midrange presence might be a bit much. To my ears, it does make a very nice pairing with the Sennheiser HD600s, complimenting their inherently recessed midrange.

With the Sennheisers through the transformer output of my EC-01 fix, I noticed a couple of key differences. The bass became tighter, faster and had more apparent extension. Craig had mentioned that the amp might be a bit too fast for the relatively slow and thick-sounding Germans. Through the transformers, my opinion here changed completely. Through the stock output, there appears to be a slight mid/upper bass bloom that makes it sound like the cans are dragging just a bit behind the music. The transformers clean up this drag. Craig had mentioned that "the high impedance headphones have a huge bump at resonance. Where they are averaging 300 ohms or so, they can peak at 620 ohms at around 90Hz. So an amp with a high source-out will have a rising voltage between about 30 and 120Hz. This makes the headphones sound like they have more bass but it is exaggerated muddy bass. With the transformer, the Z-out drops and because the primary is loaded with a constant R, the frequency response of the Senns becomes maximally flat. You will hear that as tight clear bass but not tube-like bass."

My listening impressions affirm that statement. I also noticed on the Senns that the edgy forward presentation caused by the stock EC-01 was not only ameliorated by the transformers but that the entire transition between upper mid/lower treble was smoother, more natural and also more accurate than sans compensation. The whole spectrum was more balanced, linear and sounded closer to that ideal of neutrality we always joke about being able to recognize. The highs in general had a more feathery shimmer to them. The transformers do a great job at smoothing out the 8-10kHz rise and I ultimately preferred the sound with the Sennheisers through the transformer output.

What about the Grados? With the aid of the transformers, my Grado RS-1s and HP-1000s sounded absolutely marvelous. The EC-01 clearly has the current drive and output to move these transducers the way they were meant to be moved. The Grados are known for their midrange and tight snappy bass. There is a slight upper midrange emphasis that gives the Grados their slightly forward presentation, which you either love or hate. With regards to staging, Grados are a bit compressed and two-dimensional when compared to their airier German counterparts. The EC-01 and Grados proved to be a highly synergistic pairing, with the EC-01 strengthening the positives about the Grado sound while downplaying their liabilities. The RS-1 was sweet and highly textured, the bass got a bit crazy but that's why Grados are fun and why people love the RS-1, colorations and all. The highs were as smooth as butter and there was a nice sense of depth and space around the performers.

As mentioned previously, the output power of the EC-01 into the 32-ohm RS-1s increases from 50mW to 750mW with the transformer fix. If you thought the 5687 was a tube to be reckoned with, the 6N6P is a 5687 on steroids. With Grados, I personally prefer the old-school Joe Grado HP-1000s. They are more balanced and neutral, with inarguably the fastest, tightest, most tangible bass I have ever heard from a headphone. They are also free from the upper midrange bump the John Grados seem to exhibit. The EC-01/HP-1000 pairing was heavenly. Due to their studio monitoring nature, the HP-1000s can sound cold and analytical with certain recordings, especially over solid-state amps. There is an inherent leanness to the sound, which is probably more accurate but at times can impede on musical enjoyment. The EC-01 makes the Joe Grados sing, bringing the midrange just a bit forward and giving it sweetness and texture that exudes musicality. The bass remains taut and well extended, with the highs appearing to have even more extension than before. The pairing extended into the stratosphere but remained cohesive with the rest of the spectrum. Cymbals and hi-hats sparkled and shimmered without restriction. The highs are what I love about vinyl playback and the combination of Meridian G08, transformer-coupled EC-01 and Grado HP-1000 consistently delivered musical goose bumps.

There is one caveat potential buyers should be aware of. According to Craig, "the EC-01 without any compensation goes out to 200kHz or so. Very high bandwidth, very fast. The transformers in the EC/DC need that high bandwidth to translate the high frequency energy. When the EC-01 is modded to compensate for the high-impedance 'phones, the bandwidth drops to about 40kHz. This is not a problem when driving the Senns or other similar headphones but if the EC/DC is used with that mod, treble extension will fall off above 16kHz to sound slightly mellow. So you see my dilemma. If I mod all the amps and someone buys an EC/DC, they will be disappointed. If someone buys the EC-01 without the mod and with the EC/DC, they could be disappointed. So the buyer has the option of getting the amp with the mod, or without the mod depending on how they will use the amp."

If you are a dedicated Sennheiser user or exclusively run high-impedance cans, I would suggest getting the mod since the damper smoothed out the somewhat edgy presentation caused by the .5 dB rise at 10kHz. However, if you are like me and use Grados and Sennheisers, you are better off getting the EC-01 without the damper mod but with the EC/DC. The EC-01 is $349, the EC/DC is $299 and the combo is $595.

I did have the opportunity to explore some tube rolling. The previous observations were made with the stock tubes, which to my ears sound quite good. The only possible tube replacement for the 6N3P is the 6H30. However, the 6H30 cannot be dropped in without some modification to the circuit. The 6N3P operates at a higher voltage rating in the current circuit and the 6H30 would essentially fry a resistor or two. The common replacement options for the 6N3P are the 396A, 2C51 and 5670. The Western Electric 396A is way too expensive for my taste but I found a local tube supplier with an abundant stock of NOS 5670 tubes, all military spec with black plates. I picked up a Sylvania, KenRad, Raytheon and General Electric. They made subtle differences to the stock 6N3P tube. The Raytheon made the midrange a bit too forward for my tastes but featured lots of depth and layering in the soundstage. The Sylvania had a nice balanced presentation that leaned a bit to the warmer, smoother, lusher side. The KenRad I didn't spend too much time with as it was essentially a shoe-in for the stocker. My favorite was the General Electric - great balance, cohesive from top to bottom, great bass extension and slam. Each of those tubes cost $10 so tube rolling is pretty cheap. Most users should be more than happy with the stock tubes, but you may want to experiment a bit later to tailor the sound to your specific setup.

I spent the majority of my time using the EC-01 through the transformer output. I have had numerous amps in-house over these past couple of months and while each has received equal time with me wearing the reviewer hat, whenever I wanted to listen purely for enjoyment, I always went to the EC-01 first. In addition to critical listening, I also sample amps from a more casual, laid-back mind set. Then I usually pick a random amp and surf the web or play some PS2. I might jam on the keyboard along with the recording and try to transpose a solo or do some harmonic analysis to keep my chops. With the EC-01, I always found myself too immersed in the music that I simply couldn't do anything other than sit back, relax, close my eyes and go off. This ability to simply listen for pure enjoyment and satisfaction is what defines a component as "musical". The EC-01 simply reaffirmed that notion and thus was a somewhat unique experience for me. She was one of the easiest amps to listen to. She was incredibly effective at being utterly distracting. The EC-01 review was the most enjoyable review I have written so far. Craig Uthus is knowledgeable, very honest, upfront and by user accounts on the HeadFi forum, offers great service. My musical enjoyment went up to a whole new level with the EC-01 in my system.
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