December 2012

Eastern Electric Minimax DAC Plus, The Burson Discrete Op-Amp
And The Dexa Discrete Op-Amp.
With so many different combinations of tweaks, you could lose yourself among the slew of Op-Amps and tubes.
Review By Jonathan Lo

  The Eastern Electric DAC Plus has generated a lot of on-line buzz, probably because it seems to offer tremendous bang for the DAC buck. For example, my current reference Weiss DAC202u (with USB option) happens to utilize the same Sabre ESS 9018 32-bit DAC chips as the EE DAC Plus and cost 7 times more. While it would not be correct to imply that the DAC chip is the end-all of DAC design, does all that precision Swiss engineering in Weiss really worth that much more than the EE design in terms of sound quality? To answer this question directly and expeditiously for myself, I went ahead and purchased the EE DAC Plus sound unheard. Having had experience with some Eastern Electric products in the past, including the EE MInimax tube preamp, I was reasonably confident I would not regret the purchase either way.

One reason for the purchase was the ability to roll op-amps via the factory-installed op-amp sockets, which I knew would make a big difference from my past op-amp rolling experience. I was especially intrigued to try the recent "discrete op-amps" from companies like Burson and DEXA. Another reason for the purchase was the M2Tech OEM asynchronous USB input which is capable of transmission up to 192kHz, which opens up the world of computer audio without having to go through many hoops. Lastly, the EE Dac offers both solid state and tube output stages, which can be changed with one push of a button. Utilizing the op-amp options, digital input options, and output stage options, one can literally tweak this DAC to exactly suit one's tastes, which cannot be said of most DAC's from prominent audio companies, including the Weiss.

Highlights of the MiniMax Vacuum Tube DAC Plus
• Sabre ES9018 DAC chips
• Separate power transformers for digital and analog sections
• Inputs: AES/EBU, BNC, RCA, TosLink optical and USB
• M2Tech OEM 24-bit 192 kHz asynchronous USB input
• Tube and solid-state output selectable
• Phase In/Out selectable
• Sampling Rates: 16 to 32bit @ 32 kHz to 192 kHz

Sound Bone Stock
The EE DAC Plus comes stock from the factory with two NE5532P (dual) and two NE5534P (single) op-amps. The tube socket, accessible from the back, comes equipped with one Shuguang 12AU7 dual-triode tube. When solid state output is chosen, both NE5532 and NE5534 are in the signal chain, and when tube output is chosen, only the NE5532 and the 12AU7 tube are in use. When used in stock solid state configuration, the overall sound was detailed, bold, rich, and energetic, with plenty of bass power. While not as smooth and refined as the Weiss DAC202u, music was extremely involving and fun. You will not find some limp, pale, wimpy, and overly-refined sound with the EE Dac; the listener is more likely to be bobbing his head and moving his feet to the groove and simply getting into it. A strong, forward, and dense center image anchors the soundstage, while instruments at the edges of the stage can easily be heard and seen, a nice 3D performance for a somewhat budget DAC. Detailed and exact descriptions of things like soundstaging, level of resolution, and tonality changed with different op-amps, but the general stock sound quality was already very high and enjoyable.

The tube output stage option can be a blessing for many audiophiles, especially for those who do not employ a good tubed component or two in the system. Interestingly, the sound quality difference between solid state and tube output on the EE Dac was not as large as one might have guessed. With the decent stock Shuguang 12AU7, the tube output had a smidge more bass warmth, a bit more uneven upper frequencies, and some of that tube harmonics, which some may call "tube distortion." My system already sports a highly-modified and tweaked Transcendent Grounded Grid tube preamp as well as tweaked-out 2A3 tube amps, so EE DAC's tube output really was not needed to add additional tube magic. In fact, the solid state stage came across as slightly more pure and transparent in my system, but the preference could easily run the other way for systems with less tubes.

Tube And Cable Rolling
With a bevy of 12AU7/5814 tubes in my boxes, I did roll a bunch of them into the EE Dac. Without going into excruciating detail about various tubes, I will mention a few. The often-recommended Psvane 12AU7 was indeed cleaner and clearer, although the degree of change was not huge by any means. E80CC tubes can be rolled into EE DAC without problems, and the Tungsram E80CC did what it usually does, i.e. dynamic, large, and detailed. Raytheon 5814 brought its usual refinement, balance, and clarity, proving once again its well-deserved reputation. The rare Siemens 5814A early long-plates are one of my favorites, and it did power forward with its supreme resolving capability, speed, and cleanliness. However, since the EE DAC Plus also tends to lean in that similar direction, the combo was perhaps a bit too much of a good thing in this instance in this system.

Going forward, I ended up taking out the tube altogether and using the solid state output for most of the op-amp rolling. Taking the tube out did improve the sound a bit in terms of clarity and ease, probably by reducing the power demand on the power supply. It's also reasonable in order not to continue using up tube life when only solid-state output is used. As usual, USB cables and digital cables made their differences. I settled with the Cardas Clear USB cable, which is probably too underrated in the boutique USB cable world. Now it was time for some serious op-amp rolling!

Traditional Op-Amp Rolling
NE5532P (dual) and NE5534P (single)
This is the stock set of op-amps that ships with EE Minimax Plus DAC, and they are probably a well-reasoned, affordable choice since they sound quite likable with a smooth, rich, warm sound that will nudge some "digital" sounding CD's into the direction of analogue, vinyl type of tonality and naturalness with plenty of "chest" in male vocals like Leonard Cohen. These are not the highest-resolution op-amps, but since the Sabre DAC's tend to have plenty of detail resolution, the overall level of resolution is still high, and if the DAC owner is not the tweaking, DIY type, he could easily stop right here and be happy. It is easy to dismiss these early on as "cheap stock" op-amps and not really give them the proper audition, which would be a mistake. Compared to many of the high-speed, modern op-amps, the NE5532/34 offers a uniquely lower and denser tonality, which may just be your cup of tea.

LME49990 (single) and dual-LME49990 adapters (dual)
LME49990 (single) and dual-LME49990 adapters (dual). 
These tend to be polarizing in user opinion, as some detest them while others adore them, and it’s easy to see why. Compared to NE5532/4, these are like turning up the contrast by two notches and brightness by one notch on your TV while taking sugar out of your coffee. Even recordings that are usually a little dull and low in detail come alive with these op-amps, which present break-neck speed and much more defined, detailed images. Thwack on the drum comes across with more tensioned bounce and purpose while any blur or boominess are history. Since the asynchronous USB input tends to be a little more forgiving than S/PDIF, some people may find the USB input to match better with LME49990, and those with single-ended triode amps may fall in love while those with straight-up solid state amps may complain they are "bright" or "ruthless". While their tonality is definitely much sunnier than something like NE5532, they are so clean and even, as usual, it all depends on system synergy.

OPA2604 (dual)
I had high hopes for this one, as many have reported good success with these in the dual op-amp position. However, I preferred the stock NE5532P, which preserved instrumental and vocal texture better without highlighting image outlines. OPA2604 reminded me of when too much noise reduction is applied in photography; image has clear and shiny outline but inside the image, small textures and details have been smoothed over too much, leaving a bland, lifeless subject. This may be what some look for if they want nothing to sound like a digital recording and no album to have grating moments, but other op-amps represent a more realistic rendition.

LM6172 (dual)
These sound like what OPA2604 should have sounded like, filling clearly-lit outlines with nice amount of texture and micro-detail. This is a high-speed op-amp with 100 MHz bandwidth and 100 V/us slew and can be touchy in certain circuits, ending up oscillating. Staying true to the high-speed pedigree, tonality is a little speedy, meaning airier and brighter than something like NE5532 which has only 10 MHz bandwidth and 10 V/us slew rate. Truth be told, NE5532 has more of what audiophiles call tone and naturalness, despite (because of?) the slower speed. LME49990 is categorized as ultra-low distortion, ultra-low noise and tends to draw up the image density a little tighter and more detailed than LMy6172, especially in upper-midrange. It, however, is less forgiving compared to LM6172 regarding recording flaws.

OPA627 (single)
This is an outstanding op-amp for audio use, and unfortunately one of the most expensive. While not as fast or high-bandwidth as many recent op-amps, OPA627 magically combines generous tonal richness with natural clarity, which is a tough feat for any op-amp. Compared to NE5534, there is extra life, resolution, and that sparkle which keeps one glued to the seat. LME49990 followed by OPA627 in the circuit seems to strike a nice balance in terms of musicality, tone, detail resolution, density, and speed. While OPA627's tonality can be said to be on the meaty side compared to something like LME49990, it doesn't quite cross into the obviously chest-resonant mien of NE5532.

OPA827 (single)
Whenever OPA627 is mentioned, OPA827 tends to be mentioned as an alternative. Ti categorizes OPA827 as "low-noise, high-precision" op-amp, and while its slew rate is not as fast as the LME49990, its sound does not seem slow at all. While there are similarities in sound between OPA627 and OPA827, they do sound different enough as not to be interchangeable. Compared to OPA827, OPA627 seems to add a slight but pleasant amount of sparkle to female vocals, not enough to be bright or grating but just enough to direct a little more attention to vocals. OPA627 probably adds a tiny bit of girth to lower-mid to upper-bass as well, which can sound more impressive. However, OPA827's even and neutral balance makes it sound closer to something like the very neutral DEXA discrete op-amp compared to OPA627, NE5532, etc. Once again, the neutrality sword is double-edged, but it can be a useful tool for those who know how to season their system with many different spices.

Discrete Op-Amp Rolling
Burson Discrete Op-amp
If one thought OPA627 was expensive, Burson discrete op-amps are an order of magnitude more expensive, not to mention the massive size compared to the ordinary op-amps. In fact, these are so large that the top cover of Eastern Electric Dac Plus needs to stay off in order to fit them. So why would anyone want to use something like this? While some outstanding overall sound quality could be achieved through all the traditional op-amp rolling, there was usually a nagging sense of slight grain to the tonal textures, at a level almost subliminal and in varying amounts depending on the particular op-amps in use and recording quality. One may not even notice it much on clean, well-produced albums, but on much of popular music, this grain could lead to hardness, which in turn led to the listener's inability to relax 100% completely in the listening seat. Burson discrete op-amp gets rid of this effect to the point I found myself easily transported into the music with relaxed neck muscles. When pumping up the volume with rock, ordinary op-amps grow more tiring with increasing volume, to the point one does not dare turn the volume up any higher. Bursons let you crank it up without grain, brightness, or distortion getting in the way of enjoyment. Does this mean Bursons are rolled-off, smoothed-over, or less detailed? Casual listeners may come to such a thought, but they would be incorrect. When one shifts attention to specific parts of he sound on recording he knows well, all the detail is just as present, often more so, but the lack of artificial highlighting or abnormal contrasting just makes the soundscape more soothing. Make sure to let these huge op-amps burn in continuously for awhile, which will deepen the seductive tonal palate and burn away a layer of haze.

www.BursonAudio.com

DEXA Discrete Op-Amp
It is interesting, but perhaps unsurprisingly the DEXA discrete op-amps also share with Bursons the complete lack of what I would term op-amp grain mentioned earlier. There is just none of that slight textured grain to the images and backgrounds prevalent with ordinary op-amps. Drawing analogy to photography, if ordinary op-amps represent photos shot at highish ISO of say 800, Bursons and DEXA's represent perhaps ISO 100, being much more clean and grain-free. Does it mean Bursons and DEXA's sound the same? Not at all. While both share a clean canvas, they paint with different brushes. To draw a rough comparison, one could describe the difference by saying DEXA is like Burson with a little bit of energy transferred from upper-bass/ mid-bass to low-treble/ upper-mids. As implied, Burson comes across a bit richer and meatier while DEXA seems a fraction more airy, sparkly. When a kickdrum is hit, there is more bass mass and impact with Burson, but the bass is more controlled and defined with DEXA. A lot of the popular music sounds a smidge more tolerable with Bursons, while the best audiophile recordings probably sounds clearer with DEXA. Personal preference and system synergy will dictate one's ultimate preference here, and I suspect systems with more tubes in the signal path will synergize better with DEXA. Before passing judgment on DEXA, one should give them plenty of continuous burn-in, before which they can sound a little uptight, cool, and detached. Several days' worth of continuous playing brought forth their true character, which is clean, clear, neutral, resolved, sounding neither thin nor warm. Some op-amps "seem" resolving and neutral, but the DEXA truly lets one gaze deeply into the recording without adding significant artifice of its own.

DEXA New Class-D
There is no law preventing mixing and matching of these op-amps, and great results could be obtained by mixing Bursons with DEXA. Their size difference is rather remarkable.

Having tried Burson duals with DEXA single op-amps and vice versa, the resulting sound can be said to be somewhere in between in character. There is a tiny difference depending on whether Burson comes before DEXA or the other way, but the general impression was similar enough as not to matter too much. A smart way to choose may be to choose the combination with the least amount of expense involved. It was also perfectly viable to use a discrete op-amp in one place and a traditional op-amp in another place. Something like Burson followed by OPA827 and DEXA followed by OPA627 produced wonderful results as well, and the exact combination that will work for a given system cannot be predicted with certainty without trying.

Now What? Is There A Conclusion?
With so many different combinations of tweaks available, it is easy to lose oneself among the slew of op-amps and tubes. It requires a high level of concentration and diligence in order to keep meticulous track of what is really heard and what is imagined, and I recommend intermittently going back to the stock configuration to sort of "reset" the brain and draw valid conclusions. After everything is said and done, the stock machine with stock NE op-amps produces quite special sound quality already. If coming from ADxx or CSxx DAC chips from a generation or two older, a well-engineered Sabre DAC can be an eye-opening experience in terms of sheer resolution unleashed. However, if implemented incorrectly or matched to the wrong system, there is no guarantee Sabre DAC will be both detailed and musical. However, there is no denying that EE DAC Plus is hitting way above its price class, even in stock form. Roll in some nice op-amps, maybe even some discrete op-amps if budget allows, and this capable DAC can further be shaped and molded into a digital source just perfect for a given system. Eastern Electric, Burson, and DEXA should all be congratulated for their fabulous products, which all end up giving us audiophiles more and better choices.

Specifications
Type: Digital to analog converter
Frequency Response : 10 Hz to  40 kHz
Sampling rates : 16 to 32 bit, 32 kHz to 192 kHz
Dynamic Range : 135dB
Digital Input Impedance : 75 Ohm
Tube 3K ; Solid State 200 Ohm
SNR Ratio: Tube 105dB, for solid-sate it is 120dB
THD : 0.2%(Tube) 0.02%(Solid State)
Main Voltage : 120V, 230V, 240V switchable
Dimension: 320 x 220 x 58 (LxWxH in mm)
Weight: 4.5 lbs
Price: $1100

Company Information
Eastern Electric Audio Dealer 
Morningstar Audio Imports 
44 East University Drive, 
Arlington Heights, 
IL60004

Voice: (847) 255-1150
Website: www.MorningStarAudio.com