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April 2006

Enjoy the Music.com Review Magazine
Mhdt Laboratory
Paradisea and Constantine DACs
A tale of two DAC units.
Review By Joe Audiophile (Scott Faller)
Click here to e-mail reviewer


Mhdt Laboratory Constantine  I've got no doubt that you are asking yourself, who the heck is Mhdt Labs? Well, lets see if I can help fill in that gap.

Not too long ago one of our readers dropped me a note asking about some different DACs that were available on the market. He was in the market for a good sounding, affordable tubed DAC (aren't we all). We talked about the usual suspects. I brought up the Hagerman Chime, the Scott Nixon tubed DAC, the Audio Note DAC Kit 1.1, the Musical Fidelity TriVista and a few others. I even brought up taking a vintage California Audio Labs DAC and sending it to somebody like John Hillig at Musical Concepts and having it modified. One of the local guys uses a CAL Alpha modified by John and it's stunning compared to my stock CAL DAC.

At any rate, the reader wasn't overly interested in a kit which is by far the most affordable. The other DACs we talked about were getting little on the pricey end of the spectrum. As I thought and searched, I didn't come up with a thing to help him out. Then one Saturday I called my mate Geoff over in France. Geoff knows all things cheap and great sounding. He told me to do an eBay search for a DAC. He mentioned that when I got all the hits, take a look at the ones from Taiwan. He mentioned a certain builder made one heck of a good sounding DAC for not much money (Geoff couldn't remember the exact name).

Mhdt Laboratory ParadiseaSure enough, I did a search at eBay and found a guy offering several different designs, including a tubed DAC for not much money, relatively speaking. I looked at his feedback and noticed he had hundreds of sales without a single neutral or negative feedback. The manufacturer was Mhdt Labs. So I decided to drop them a note and see if he was up for a review. Of course, they jumped at the chance.

Mhdt Labs offers four different offerings in their line of DAC's. Two of the DAC's are standard solid state and the other DAC's utilizes a tube as a buffered output stage. I asked Jiun-Hsien Wu, Chief Designer for Mhdt Labs if he would be interested in sending one of his solid state DAC's along with the tubed DAC. Sure enough he agreed and sent the Constantine (solid state) and the Paradisea (tubed).

I've stated over and over previously, that I don't know anything about DAC designs, so don't get the idea that I'm going to try to impress you with digital drivel. One thing I do know about is the quality of parts and the importance of a good layout. That is what initially drew me to these units. I'll pepper the design section with bits I've read on the net but I can't attest to their accuracy. In the end, I can tell you exactly how these two little gems sound. That you can take to the bank.


Basic Design
Let me start by recapping what Jiun-Hsien Wu of Mhdt Labs states about their DAC units. Both of the units on hand utilize the Philips TDA 1545A non-oversampling (henceforth know as NOS) DAC chip. The TDA 1545A has 16 bit resolution. The units have a dual voltage power supply transformer that can accept input voltages or 110 or 220 at either 60 or 50 Hertz. Both DAC's can handle Toslink, RCA coax or BNC digital inputs. The printed circuit boards are fiberglass FR4 94V grade, which meet the UL-94V-0 standard (as I'm told). This is more than ample considering the B+ rails of the digital section is running under 15 Volts (see later text for the tube buffer operating voltages).

The cases are constructed from a 5mm smoked, transparent acrylic. The cases are etched with the Mhdt Labs logo and the name of the DAC. In the case of the Constantine (the tubed DAC), Jiun-Hsien Wu has laser cut ventilation holes in the top of the casing to allow the heat buildup from the tube to escape. On both units, the left and right sides are open to allow ‘flow through' ventilation.

You might be concerned about the fact that these are ‘handmade' pieces of gear. I'm here to tell you that the fit and finish on both of these DAC's are stellar. You'd swear that these were production pieces rather than something hand cut, drilled and assembled. They are beautifully made.

Mhdt Labs has their transformers custom wound for both DAC's. From top to bottom, these DAC's are using quality passive parts. You'll find cottage industry names like Rubycon (ZA and ZL series) capacitors, Sanyo OSCON, Elna and Silmic capacitors used throughout. Mhdt private labels their own metalized polypropylene capacitors used in the signal path. There is also a combination of Dale RN series, carbon composition and other metal film resistors used throughout the DAC's.

The active components used in both Mhdt DAC's are the NOS 1545 DAC. The Constantine uses the Analog Devices 826 opamp and the Paradisea uses the Burr Brown OPA2604.

As I understand from talking to someone that knows more about digital design that I do, Mhdt Labs has chosen the same route that Audio Note does with their DAC's, they don't incorporate the ‘brick wall filter' in their designs. There are people within the industry who feel that this is ‘improper' design, but then there are people who design by listening and deciding what sounds best. Mhdt is in the latter camp. I'm not saying who is correct, just letting you know there are two different philosophies out there.


The Paradisea's Tube Buffer
The Paradisea DAC uses a single 5670 vacuum tube. This tube is directly coupled to the output of the Burr Brown OPA2604 opamp. Mhdt Labs is not using a coupling cap, resistor or transformer between the opamp and the grid of the 5670 vacuum tube. In other words, the 5670 tube is directly coupled to the opamp using (essentially) a modified Loftin-White design. Mhdt has chosen a slightly larger output coupling cap for the Paradisea, a 1.5uF as opposed to the 1.0uF used in the Constantine.

The Paradisea can take various equivalents like the 2C51, Western Electric 396A, 6N3Pi (6H3pi), or the 6CC42. The great part, the most expensive of these tubes is the Western Electric. At last check on eBay, the WE396 was selling for under $20 bucks. The vast majority of these tubes will run you between $4 and $6. That means you can pick up scads of different flavor tubes and still have plenty of money left over for pizza and beers.

Jiun-Hsien Wu has added a separate transformer and Pi filter to handle the load and regulation of the tubed buffer stage. Mhdt Labs has chosen to run the tube at a very low voltage. Jiun-Hsien Wu picked 19 Volts as the B+ operating point for the tube buffer. This does a couple of things. First it extends (dramatically) the life of your tube. Second, it makes the design and size of the DAC much more manageable since you don't need a big honkin' transformer and high voltage caps for the Pi filters power supply.

Just a quick word about the buffer stage for those not familiar. A pair of nice sounding opamps, the Burr Brown OPA2604's, handles the gain stage on the downstream side of the internal Philips 1545 DAC. Just downstream of the output opamps resides the 5670 vacuum tube. This tube adds a nominal amount of gain to the output stage. The tube acts as a buffer, which gives the DAC the tube qualities that many of us have come to know and love. In other words, the design of the Paradisea is not a true tubed gain stage, it is merely a tube buffered output with the critical gain stage being handled by a pair of quality opamps.


A Non-Statement About Digital Sampling Rates
In the realm of digital to analog conversion, there are hugely differing opinions as to which method of conversion sounds the best. We have non-oversampling (as is the case with the Mhdt Labs DAC's), we have oversampling and we have upsampling (notice I left out SACD as I'm only speaking of Redbook).

The camps out there will each defend their chosen sampling procedures to the death (if need be). I've found that each of them can sound quite good when done well or quite bad when done poorly. In my case, I've got the AH! Njoe Tjoeb which allows me to use the stock output of the Philips TDA 1545 along with the OPA2604 (or the AD 826) opamp or I can drop in the 24/192 upsampling board if I so desire.

As for my preference in sampling rates, I like them both, but I vacillate. I'll go for a while listening to the stock, NOS chip and then I'll get a wild hair and install the upsampling board and listen to it for a few months. Then I get bored and yank the board back out for something different. As you can tell, I really don't have a preference. I sort of sway with the prevailing winds. I just like the breeze.

When it comes to the sonic differences between the two sampling rates, hopefully I can explain them without causing some sort of flame war or getting too many email bombs. The upsampled units that I've heard tend to exude a large amount of (apparent) detail. I said ‘apparent' because of the mathematic interpolation an upsampler does. The upsampler samples the information on a CD and then ‘approximates' the additional detail through a complicated algorithm. Upsampling (as I understand it) stretches the data points apart (of sorts) and fills in the gaps with approximated data, smoothing the data stream curve. The end result is, the upsampled signal that comes out of your speakers supposedly has higher resolution. You hear more detail, there is a greater breathiness to the sound on your CD. As I stated earlier, done well, upsampling can sound very good. Done poorly, it can sound like cats mating. Upsampling can also bring the soundstage quite a bit more forward into your room. And yes, just ‘average' upsampling can be quite harsh, fatiguing and can have a definite digital sheen to it.

In a back to back comparison between the two, non-oversampling can sound a bit dull and lacking in detail. But, after your ears become accustomed to the non-oversampled chip, you begin to understand that the presentation becomes far more relaxed and less aggressive. I hate to use this term but it sounds less forced. In essence, less digital sounding. Even though it isn't vinyl, it contains a few more of its qualities (IMO) than its higher resolution cousin, upsampling.

I guess what I'm getting at is the differing sampling rates are ultimately a personal preference. Each can sound quite good when done properly. If you want some seriously technical information regarding sampling rates, do a Google search using "upsampling vs. oversampling" as the search parameter. You'll get enough reading material to keep you going for weeks on end.


So Lets Talk About How They Sound
The vast majority of my review of the MHdt Labs DAC's were done using the Bolder Cable modified Squeezebox and the Rev 1 Power Supply. I used my DeZorel mains conditioners in front of all of my gear. Since the Constantine and the Paradisea are essentially the same design with the only major difference being the tubed buffer stage of the Paradisea, they sound quite similar. The difference being the restored dynamics and the naturalness the tube provides.

When directly comparing the two, the Constantine comes across with a light, delicate touch to the music providing loads for detail without coming across as being aggressive or overbearing. The Constantine is quite dynamic and paints a sharper sonic picture. The Constantine provides slightly better imaging. The sonic musicians are just a tad better defined in the holographic space we all love so much. As I listen I find the bass and midbass response of the Constantine slightly less pronounced when compared to the Paradisea. I suspect it has to due with the tube buffer stage of the Paradisea. In turn, the bass of the Paradisea has more weight and impact which may or may not be what you are liking for in your DAC. The bass of the Paradisea is quite firm and authoritative when you pick the right tube (more on tube choices later).

Comparing the two (at least in my system and with my heavy preferences for tubes), the Constantine can seem a bit thin in the bass and midrange. Don't read that as being a negative attribute because it isn't, it's just my preferences coming out. In fact, another hardcore SET and Lowther I know (and you all know too) and respect fan thinks the Constantine sounds more ‘real' than the Paradisea. Again, it all comes down to personal preference.

Keeping my preferences in mind, I find the Paradisea has a more accurate timbre than the Constantine. The tube restores some of the dynamics to the original compositions. Though I'd prefer a true tubed gain stage as the output of a DAC, the combination of a quality opamp and the tubed buffer stage works in concert extremely well. The Paradisea gives up a little definition and polish for more authority and dynamics. At the same time the Paradisea gives you a very slightly wider and deeper soundstage.

Guessing at your personal tastes here, if you are a detail freak, the Constantine is the logical choice for you. It does a great job. Its very well suited to you solid state guys out there. The Paradisea falls right into my musical sweet spot. The authority and weight it projects is a perfect match to my system. It isn't the least bit fatiguing. To me in my system, the Paradisea sounds more like real life. Don't misunderstand, they both have their faults but in the same vein, they both sound extremely good.

The great part is neither of these units show any hints of veiling the music in the least. They both are some of the cleanest and most accurate NOS DAC's I've had the pleasure of listening to. Granted, pick the wrong tube for the Paradisea and you'll hear some sonic goo, but the tubes are cheap and very readily available. It's more than obvious to me that Mhdt Labs listened first and then looked at the bottom line last.


Roll Your Own
As I've mentioned, the 5670 tube and its variants are cheap and readily available. To date I've found 6 different variations of the 2C51 tube. Each one has its own unique flavor. The Paradisea ships with a new old stock JAN GE tube. It sounds just fine. As I started collecting different brands I found that in my system the black plate Bendix sounded the best, even better than the Tungsol's I picked up. The bass was nice and firm and the treble was crisp, clean and extended.

I haven't gone to the point of searching out every variant out there and giving them a listen. The owner of Mhdt Labs seems to like the sound Western Electric 396A. One of these days I'll run across one other than on eBay. Last thing I want is to get into a bidding war and pay more than the tube is worth.


Lets Talk About Some Music
In my time I've spent with both of these fine sounding DAC units, one of the songs I was most taken by was Eva Cassidy's "Fields of Gold" (the Sting classic) from the Songbird CD. Every time I put this CD on a good CD player, I usually end up having to listen at lower levels because Eva's voice gets butchered by jitter and God knows what else. I have to say that the combination of my Bolder Modified Squeezebox and the MHdt DAC has made this CD sound better than I've ever experienced before.

Eva actually takes on weight and proportions. The notes from her guitar leap from my Lowthers. I'm hearing layer upon layer of detail just as it was recorded. Her voice has that chestiness that drew me to her initially. There is ZERO hint of grain or edginess coming the Paradisea. The highs are nice and extended. I can also plainly hear the gentle tape hiss from the analog masters.

Listening to Lyle Lovett and his Large Band doing I Know You Know, these guys absolutely come to life with the Paradisea. From the gentle touch of the brushes swirling around the drums to the ever present strumming of the hollow bodied rhythm guitar coming from the left channel, the sounds are deeply dynamic and extremely well defined. Lyles voice carries the presence not often heard from lesser gear. He comes to life with the help of the Mhdt Labs DAC units.

Moving onto something a bit livelier, Robben Ford's Up The Line has Robben matching lead guitar notes with a baritone sax in portions of the song. The sax has this big phat sound that is just nearly perfect. The overlaid instruments are easily distinguishable. The Paradisea and the Constantine don't cover up any of these complex music passages.

Next up is easily one of the most dynamic CD's that I own. Ronnie Earl's Still River on the Audioquest label. It's now long out of print. Listening specifically for that ultra cool Hammond B-3's intonation, each of the DAC units do a fabulous job reproducing its sound. The B-3 comes through on both units as the warm, wonderful organ that it truly is.


Side Story
Funny, not long I was in an antique shop and I was asking the owner if she had any old radios or vacuum tubes in the shop. She said no but then stopped me and said she had an old organ in the back room. She mentioned she couldn't figure out how to turn it on. She said it made noise like it was running but they couldn't get any sound out of it.

When I looked at the organ I saw it was a Hammond. I spun it around to see which model it was I saw the tag that stated it was a M-3. Not quite the caliper of the B-3 but a great sounding organ nonetheless. I reached under the keyboard and flipped the on switch and then pushed the start motor for the speaker. Once the oscillator got up to speed I engaged the drive and she was playin' music. Not anything recognizable since I was at the helm but some really cool sounds were coming out of this vintage organ. I showed the owner how to get the organ running and talked to her for a little while her mom played some gospel music and hymns and then I set myself down the road again.

Sorry, I got sidetracked


In The End...
The sounds the Paradisea and Constantine produce are nothing short of lovely. So few non-oversampling DAC's get the music right top to bottom and this happens to be one of those occasions. Its not very often I get a piece of gear in the old homestead that can make my nipples stand up at attention but this one does it (I know, that was probably too much information but you guys know me by now). Truly, the MHdt Labs Constantine and Paradisea DACs have made me forget that I'm listening to gear. When I listen, all I hear is music, magnificent and pure just as it should be.

When it comes to which one is best for you, that could be a really tough choice. Both are truly excellent sounding units that will absolutely hold their own with the heavy hitting non-oversampling DACs out there. If you are a solid-state guy looking to see what tubes might do for your system, the Paradisea is a great choice. The tubes are cheap and easy to find. I really think you'll like what you hear. If you are a tube guy at heart, the choice is obvious, you'll love the Paradisea.

If you are a detail freak or don't care for the sound of tubes, the Constantine should be best suited for your system. It's clean, accurate and doesn't come close to hinting at listeners fatigue. If you're a tube guy and your system is just a bit too ‘tubey,' take a hard look at the Constantine. It does a great job and should tighten up your digital front end quite nicely.

Both of these DAC units are truly soul stirring...  and the best part, they're cheap compared to much of the competition. Are you guys looking for a giant killer? These little David's are hiding in the bushes if you are willing to look outside the traditional purchasing paths. Will either of these miraculously transform a crappy recording and make it sound like something from Sheffield Labs? Not hardly. Will this little pair of DACs make those marginal recording sound considerably better? Absolutely. They will also take all of your favorite audiophile recordings and it will breathe new life into them.

Keep in mind, as it is with all small manufacturers, Mhdt Labs crank gear out as quickly as time affords. They don't have huge factories with dozens of assemblers and automated soldering lines. The small manufacturers usually have a backlog that may take a few weeks (or longer) to plow through before the piece you ordered gets built so try to be patient.

Both of these pieces come with my highest recommendation based upon their tremendous sound and their miniscule price tag. And don't think for a minute that these can't compete with the big boys out there, because they can, easily.


My Ratings
Please keep in mind this rating system is used to compare the Mhdt Labs DAC units against absolute perfection, or cost-no-object DAC design. If you see what you think may be a low(ish) score, it's because there are DAC designs that are even more refined but consequently cost considerably more. To top that off, if I assign 5's across the board, I've just painted myself into a corner leaving no room for that ‘ultimate' DAC. You won't see me handing out many 5's. In turn, I feel I need to leave room in the ratings system to accommodate those DAC units.


  Constantine Paradisea


Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High-frequencies (3,000Hz on up)



Inner Resolution

Soundscape width front

Soundscape width rear  
Soundscape depth behind speakers

Soundscape extension into the room


Fit and Finish

Self Noise

Value for the Money


Type: Stereo digital to analog converter

Frequency Response: not available

Output Voltage: not available

THD: not available

Inputs : Coaxial (RCA and BNC) and Toslink - switchable

Tube Complement (Paradisea): 5670 (or equivalent)

Weight: 2.5 pounds each

Dimensions: 23 x 6 x 15 (WxHxL in cm)

Price: Constantine approx. $375 (eBay), Paradisea approx. $500 (eBay)


Company Information
Mhdt Labs, Taiwan
Proprietor: Lin-Li Chuang
Designer: Jiun-Hsien Wu
E-mail: mhdtgang@yahoo.com
Website: www.geocities.com/mhdtlab/












































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