Eastern Electric Minimax Tube DAC Plus

Eastern Electric Minimax Tube DAC Plus

The 4 op-amps in clear view. The two white plastic capacitors are coupling caps for the tube output stage

A closer view. The OEM M2Tech USB board is at the rear of the unit

The subject of this review is the Eastern Electric MiniMax Tube DAC Plus (which I will refer to as the “Plus”), which is an upgraded version of the original Minimax DAC. The original Minimax DAC was based on the Sabre ES9018 DAC chip and was unusual in offering a choice of both a solid state and tube based output stage (using a single 12AU7 tube), and volume control.

In comparison, the Plus loses the volume knob and upgrades its crippled USB input (red book only for the original version!). There are also a number of component changes, including an upgrade to separate power transformers to handle its digital and analog sections, and some fine tuning in the power supply and tube output stage.

Input flexibility remains excellent with a total of 5 inputs, USB, BNC, RCA, Optical and AES / EBU. The USB port (sourced from M2Tech) now supports up to 24/192 kHz sampling rates and is asynchronous.
Output is single-ended only. Why no balanced outputs considering the ease of implementing this out of the ES9018 ? I presume this is because of the single tube stage. Having a tube stage for balanced operation would require a second tube at the very least.

The front panel (like the original version) also offers on-the-fly switching between the tube and solid state output stage, as well as phase inversion. The unit does not remember user settings and will revert to the tube output stage as a default when switched on.

The tube output stage is constantly energised once the unit is switched on, so you can forget about leaving the unit on permanently unless you listen to the solid state output stage, and remove the tube from its socket all together.

Physically smaller than standard component dimensions, the Plus is best described as a slightly shrunk 2/3 scale model. Fit and finish are very high for the price and operation of knobs and buttons always feels solid and reliable.

Thankfully, tube replacement is relatively easy, as the tube is accessible from the rear panel. However, it is a bit fiddly as there is a tube damper / shield to remove first. The tube sockets are very tight and physical space is limited to pry the tube out from. Users are best advised to remove the top cover first before trying to remove the tube - the additional space on top makes this a far easier task.

This unit is well run in having been bought second-hand. The Plus replaced the Calyx 24/192 DAC on my equipment rack. Both units were setup in the same way, fed by a 2011 Mac mini running Pure Music 1.84. The digital signal is then fed via USB to the DAC. For USB cable purposes, I alternated between a L A T USB-2 cable and my regular cable, the Entreq Konstantin (hooked up to the MinimUs ground conditioner)

Sound quality

Initial listening experience with the Plus was disappointing. After a good 20 minute warm up for the tube stage, the Plus was clearly not as resolving as the Calyx, with a slightly vague and hazy presentation. Somehow, the ESS Sabre micro-detail magic was missing. Who let the pixie dust out of my system ?

Switching to the solid state output stage was a wholly different matter. The characteristic ESS Sabre sound was back. Being a dyed-in-the-wool tube person, this was somewhat disappointing. The sand based output was clear, incisive, with both more 3-dimensionability and authority. Arguably, the only advantages offered by the tube output stage was a slightly thicker tonal density, more mid-bass bloom and smoothness.

Most of my listening was eventually done on the solid state output stage with upgraded op-amps, which is covered in greater detail below.

The Plus would be best described as a smooth operator, with a slightly warm and laidback tonal balance. It would never be accused as being bright, but cleverly avoids sounding overly warm and woolly. Consistently even handed throughout the frequency range, the Plus does not overemphasize any part of the frequency specturm.

Bass is tuneful and would be considered as class average in terms of impact and extension. Drums and double bass have suitable impact and depth respectively.

Midrange is smooth and detailed and the human voice is quite engaging. I noticed though that the voicing on the midrange is warmer and sweeter than usual. Listening to Eva Cassidy's album, "Live at the Blues Alley", Eva's characteristic clear and sometimes piercing voice was thicker and sweeter than usual. The usual sibilance problems with her voice also seemed to be greatly reduced.

High frequencies are detailed and extended, with equal emphasis between the leading edge and reverbation from crash cymbals. In comparison, the Calyx has less snap on the leading edge, with greater emphasis on reverbation.

Soundstaging wise, the Plus has a more intimate presentation compared to the Calyx 24/192, with the impression of being seated at least a few rows closer to the performance.

Image sizes are slightly larger compared to the Calyx, but with less definition overall. If you like your voice and instruments to have more body and density, you will like the Plus.

In terms of resolving power, and separation, the Calyx is clearly superior to the Plus. The Calyx keeps its composure under the heaviest of mixes, and has excellent micro detail retrieval, especially at low volumes.

Op-amp tweaking

A quick search on the internet will reveal a fair amount of discussion on op-amp rolling. I tried some quick substitutions just to see the magnitude of improvement offered. The stock I/V op-amps, a pair of dual channel NE5332 op-amps were substituted with a pair of National Seminconductor LME49720 op-amps. The solid state output stage, a pair of single channel NE5334 op-amps were substituted with Burr Brown OPA627BP op-amps as well as National Semiconductor's LME49710.

After about 10 hours of burn-in, some listening tests were done. Significant gains in most areas, including bass authority, clarity and soundstaging were observed. This makes op-amp rolling a no-brainer.

As a matter of taste, the OPA627 had a fuller balance, almost sounding tube like in its bloom and liquiity. The LME49710 had more focus and speed. I preferred the much cheaper LME49710 in my system.

For the ham fisted, it would be best to get a more technically proficient friend to help. For the uninitiated who insist on DIY or death, please observe the following,

1. Dual channel op-amps must be substituted with dual channel  op-amps, and the like for single channel op-amps.

2. Ensure voltage compatibility. The Plus has a dual voltage rail of +/- 15VDC.

3. Observe strict anti-static precautions, op-amps are easily fried.

4. Be very careful when removing or inserting op-amps, the legs can be quite fragile. Invest in an op-amp puller.

Tube tweaking and rolling

Any hope for the tube output stage ? Users are advised to try removing the tube shield. I prefer the tube stage without the shield – the sound is noticeable clearer and has more “air”. I generally do not like tube damping of any form, as I find that it can easily make the sound too dark and dead.

The stock 12AU7 tube supplied is brand labeled as “Eastern Electric”. Internal construction looks very similar to Shuguang, and is presumably OEM sourced from them.

I tried substituting the stock tube with a National 12AU7 black plate (likely to be a relabeled RCA). This was much better than the stock tube, but at the end of the day, I still preferred the solid state output stage.
If you prefer the solid state output stage, the Plus sounds better with the tube removed totally - presumably this eases demands on the power supply.

Phase Inversion 

Although some discs sounded better with phase inversion, I left the button alone. It became a bit of a chore having to remember which discs sounded better with inversion. Nevertheless, this may be a useful feature to some.

Conclusion

Locally, the Calyx is almost double the price of the Plus. However, the Plus is an absolute bargain in context of its asking price.

In order not to be misconstrued as a lack of affection for the Plus, I personally feel that listeners on a tight budget should plump for the Plus. So should listeners that have a variety of sources, or would be listening primarily through the co-axial or optical input. The Calyx shines best through its USB input

The ability to tweak the unit through op-amp and tube rolling is to me, one of the strongest points of the Plus. Such tweaking is helpful to fine tune the unit to suit the end result that the user is trying to achieve.

The Plus is a competent performer at a competitive price. Well specified, and offering a choice of both solid state and tube output stages, it is likely to appeal to the masses, although I ultimately preferred the solid state output stage.

On the downside, the Plus is no giant slayer nor class leader in the ESS 9018 product class. The Calyx 24/192 ultimately has its edge over the Plus in terms of confidence, resolution and natural effortlessness.

Entreq Konstantin USB cable and MinimUs

I love organic products ! Coming from Sweden, are these delicious (but unfortunately inedible) products, which are the brainchild of Mr. Per-Olof Friberg.

Mr. Friberg is self-described as a farmer. This is a rather refreshing change from the background of the founder of some other audio companies, e.g. NASA scientist, aerospace engineer, weapons-I-Can't tell you what I made scientist, espionage agent .... OK I made up the last one.

The MinimUs came in a plain cardboard box and "interesting" packing. I opened it in front of my significant other who was half expecting to see some lovely pears packed, but no, it was just another boring audio device.

The MinimUs is a wooden case, which is much heavier than its size suggests. The wood fascia looks like it is laser engraved. The rear sports a single copper binding post. Interestingly, the binding cap is made out of wood - careful now with tightening the cap, you don't want to strip the threads.

All connector housings are made out of wood.

The single ground binding post. 

What is inside ? I have no idea. Shaking the box produces a rustling sound, much like sand. The unit is well sealed (with no visible screws), so we can forget about taking this box apart.

The instruction manual suggests that a single MinimUs can be used for up to two sources, while two boxes can be used for the speaker cables. If you go for the larger unit, the TellUs (which has 3 binding posts), you can treat the whole system.

No cables are provided, so I jury rigged some out of a unused Canare F-10 RCA plug, and some 14 AWG mains cable soldered with alligator clips on each end (which I use for my DIY tests). Entreq of course sells the required cables, in both copper and silver. Pricing is reasonable, so you don't have to resort to my measures.

The instructions warn against using the MinimUs as a replacement for protective earth. We could therefore assume this to be some type of ground enhancer. How this enhances ground, I have no idea. But it certainly enhances the sound.

Hooking up the MinimUs to an unused output (sorry, my amp is out of inputs. Ground is internally connected together anyway - verified by a multimeter), quickly shows how potent the MinimUs is. There is no superlative descriptions of lowering of the noise floor, or blacker blacks. Rather, everything is thrown into sharper focus. There is useful enlargement of the soundstage and improvement of spatial clues. However, the best way to describe this is a relative relaxation in tone, a increased sense of ease and flow, for want of a better description. I particularly appreciated that the MinimUs did not deaden the sound nor kill the sense of air, which sometimes happens when using ground enhancers / mains filtering products.

Coming to the Konstantin USB cable, more than a passing resemblance to an old kettle cord is noted. Much like the MinimUs, the Konstantin uses wood plug housings. Attached to the USB B plug side, is a female headphone socket that accepts a mating plug wire, which is intended to be attached to the system ground, or alternatively the MinimUs.

Grounding the Konstantin USB cable to the MinimUs.

First, let us be clear on the debate on whether or not USB cables make a difference. If you strongly believe that it does not, then this would be the point that you would conclude that I have absolutely no credibility. You can also pat yourself on the shoulder for the time you have saved from having to read the rest of this drivel.

For those of you still with me, you would agree that USB cables do sound different, although the "why" and "how" still remain a question mark.

The Konstantin is quite a special USB cable. It casually kicked the Nuforce Impulse cable I had lying around into the abyss of no return before coming face to face with the L A T USB 2 cable. The L A T muttered some excuse about having a dentist appointment, and turned tail in a flash.

Initial evaluations of the Konstantin were made without any grounding, which turned out to be a big mistake on my part. The first few hours with the Konstantin were not eventful. The sonic picture was a little distant and the tonal balance of the Konstantin was delicate, albeit lightweight.

An additional 10 hours of burn in helped somewhat, but the general lightweight balance remained. At this point, I took out the grounding cable, stripped the insulation at the end and connected it to the MinimUs.
Instantly, the cable came into focus, and the music took on sufficient tonal density to look like a real picture, rather than the pastel shades of water colour paint prior to that.

Want an incisive presentation with emphasis on the leading edge of notes, with explosive dynamics ? Looks elsewhere.

The best word to desribe the Konstantin / MinimUs combo would be "natural". The combo has a sense of ease and unforced naturalness that will guarantee hours of listening pleasure without listener fatigue.

Tonally, I would put the Konstantin / MinimUs in the neutral camp. Despite its musical and natural balance, this is neither a veiled nor shut in cable. It excels in both micro detail and placement of instruments. There is a noticeable increase in transparency coming from the L A T cable (let's not even talk about stock cables here).

Bass and dynamics are not of the bone crunching variety, but are both fast and tight. This cable impresses most in the midrange upwards, where the human voice is nicely balanced and is placed in fine balance between smoothness and transparency. Drum set work is a real treat, with nice impact and decay on ride cymbals, and the opening and closing of hi-hats coming across in a clear and distinct way.

This is not a cable that would immediately impress on A/B comparisons. It was only after some extended comparisons that the strengths of the Entreq combo becomes apparent. In comparison, the L A T is messy in its soundstaging, and lacking in refinement. There is a hint of harshness that is immediately noticeable when switching from the Entreq to the L A T.

Any critcism ? The first would probably be a lack of upper mid-bass bloom that could be helpful in some systems to fill out the lower registers. The second would be price. The Entreq combo (and I really see them as a system rather than as separate components) are in serious price territory. The resulting four digit price tag (in Singapore dollars) would have many chuckling at the "insanity" of purchasers. Should you care ? As one senior audiophile once told me, "Who is to say it is wrong if the money makes the most improvement in your system for the amount spent ?".

What about using the Konstantin without the Minimus ? There is a slight loss of quality if you tie the grounding wire to a normal ground source, e.g. your preamp chassis or the ground of a RCA input, but I would say that you would be missing about the final 10 % of what this cable is capable off.

I also tried this in a friend's system recently. He had recently bought the Oyaide Continental 5S USB cable. The Oyaide has a dynamic and exciting sound. It is the perfect kick in the pants if your system sounds slow and dull.

The Oyaide had a more forward presentation, with better "projection". The Entreq had superior low level detail, and refinement . Interestingly, the Entreq had superior imaging and control, with vocals and instruments locked firmly in their place. The Oyaide is less than half the price of the Konstantin with MinimUs, so you could say that the odds were stacked against the Oyaide.

I certainly would not advocate that everyone rush out to buy the Entreq. In fact, in modest set-ups, the L A T USB cable was quite impressive, especially if you consider that it costs 10 % of the Entreq combo. But if you have a very good setup, and the Entreq does it for you, then it is really is the icing on the cake. Highly recommended.

Calyx Coffee DAC and Headamp

Good things come in small packages ! Well this does not always hold true for audio equipment, but nevertheless, the Calyx Coffee is really diminutive and cute as a button to boot.

The Calyx sports the current in-thing for DAC chips, the ESS Sabre. At the Calyx’s asking price, you obviously luck out if you were hoping to get the Reference Sabre chip. Instead, you get the ES9023 which sports two D/A convertors (vs. the eight found in the Reference chip). Like the rest of the Sabre chips, the ES9023 also boasts technology such as Hyperstream Architecture and Time Domain Jitter Eliminator (the complex technical details of which overwhelm my feeble mind).

Interestingly, the ES9023 chip includes a 2VRMS driver which would presumably allow a designer to skip the op-amp stage and use the ES9023 as a single chip solution.

On the bright side, your hard-earned money gets you a 24/96khz capable DAC with asynchronous USB connection, and a fairly competent headphone amplifier. The most obvious target market for the Calyx would be in a computer based head-fi or desktop set up. Given its small size and portability, it is also the perfect traveling companion, and was in fact the reason I purchased one. Pack in a nice pair of earphones with your notebook and the Coffee, and suddenly your work trips do not seem so lonely after all.

Dressed in a shade of a rather weak looking cup of Java, the Calyx is a simple bar shaped device. On one end, you will find its single USB input, and on the other, a pair of RCA outputs, and a 3.5 mm headphone jack.

The top of the unit is adorned with a single neat row of small gold buttons, that can control the source computer, with the ability to control play, skip and volume control (including mute). Stick on rubber feet are provided, so no worries about marring the beautiful surface of the Calyx. No cables of any form are provided, which is fine with me. Most freebie cables end up in the dustbin anyway. The Calyx draws its power from the computer’s USB port and there is no option to power it from an external 5V power supply.

Shaking the unit results in an alarming rattling sound. I was worried that something was broken inside, but the dealer assured me that it was just the buttons. True enough, the rattling stops if you apply a bit of pressure on them. Other than that, build quality is excellent. There are no screws or joints on the top and sides of the unit, so the Calyx is presumably milled from a single aluminum block. The bottom plate is screwed on though, making the enclosure of the Coffee a two piece assembly.

Installation was straight forward and hooking up the Calyx to my computers running Windows XP and Mac OS/X Lion were hassle free. No drivers were required and the Calyx was immediately recognized. Everything worked as expected, including the operation of the buttons to control the volume, etc. The steps were a bit coarse though, and I ended up using the slider bar on Windows to control the volume of the Calyx.

The Calyx Coffee has enough juice to drive most ear or head-phones on the market. It certainly had no problem driving either my 250 ohm Beyer DT-880 or my Audeze LCD-2. With the latter, volume is almost maxed out, so LCD-2 users who listen very loud may want to look elsewhere. Sound quality is good, well above average and far better than you expect for its price.

Hooking up the Calyx to my main hi-fi system, I questioned the sanity of using cables (Acrolink 7N-D5000 RCA and LAT International USB 2) which were more than 8 times the cost of the Calyx. I then awaited for the David vs. Goliath moment. After a few minutes, it was obvious that my Audio-gd DAC 19 was in no danger of being outclassed by the Calyx. The Audio-gd is close to 4x the cost of the Calyx, so no surprises there.

The Calyx has what I consider to be the typical Sabre house sound - slightly laidback and hyper-detailed. Sabre chips do not have the incisive leading edge emphasis of more analytical chips, but instead presents its sonic picture in a natural way. The details are all there, but are not presented with the stark contrast and leading edge emphasis of some of its competitors.

Bass is firm and slightly full. However, it lacks slam and extension. Bass freaks will definitely not be satisfied. You could say that the Calyx is slightly bass shy but the overall quality of its limited bass is quite high.

Midrange is one of the Calyx’s stronger points with a smooth and natural human voice. The usual suspects of sibilant tracks are quite well behaved and it is unlikely that this DAC will come across as cold or harsh. Listening to Eva Cassidy's album, “Live at the Blues Alley”, you get a sense that the Calyx chooses to honey coat things. The usual sibilance and slightly piercing quality of Eva sounds very nice on the Calyx – a bit too nice to be true.

High frequencies are clean and fast, and the sense of acoustic space is well conveyed. Nevertheless, treble extension could be better and is easily bettered by more expensive equipment.

Imaging is good, but soundstaging is slightly flat, with a reduced perception of width and depth in recordings. This is very noticeable as a loss of presence and air on Janos Starker's recordings of Bach's Suite for Solo Cello. Instruments and voices are also placed further back than my usual gear, with slightly smaller image sizes.

The Calyx is also not the most dynamic DAC out there. Rock and metal lack some energy and rawness. Faster music sometimes comes across as being a bit too polite.

Detail wise, the Calyx is definitely a significant upgrade over a stock computer soundcard or chip. However, some level of microdetail is lost, which is apparent when compared to the Audio-gd.

Two things I would have liked to see would be support for a RCA digital input, and support for 88.2 khz sampling rate. The first omission is forgivable since the Calyx is clearly not intended for primary use in home systems. However, the second omission is less so. The lack of 88.2 khz sampling support deprives native decoding of some source material out there (admittedly quite rare), as well as 2x up-sampling of red book material. My personal experience with red book up-sampling, is that it sounds more natural up-sampled to 88.2 khz compared to sample rate conversion at non integer multiples, e.g. 96 khz. I know what many will say, the big brother Calyx DAC is the answer to my wish-list.

In summary, the Calyx is a great upgrade for computer audio users. It is very competitively priced and competent. I am very impressed with the Calyx Coffee and recommend it highly for a portable computer based setup, and even more so, if primary listening is being done through head or ear phones. If using inefficient or difficult to drive headphones, I would advise you to try before you buy.

For home rigs, the Calyx is a less convincing proposition. While it is adequately suited for budget rigs, spending a bit more would definitely pay more dividends in the long run. Then again, for the money, you certainly could do a lot worse.

The weaknesses of the Calyx Coffee should be viewed in context of its affordable price. When used without reference to better (and much more expensive) equipment, the Coffee is musical, offers a useful upgrade in resolution and is pleasing to the ear. It gets a lot of things right, with good tone, especially for those with a musical diet tuned more towards jazz, vocal recordings and chamber music. It is only when you do direct comparisons to other gear, that you realise what is missing. Throw in its head amp stage, and you realise the excellent value proposition presented by the Calyx.

Postscript - Calyx Coffee users should try pairing their units with the ifi iUSB power supply. This provides a significant boost to the performance of the Coffee.