Modifying the MHDT Atlantis DAC

MHDT has a cult following in the DAC world, and for good reason. They may not all be featuring the latest chip designs and 768kHz inputs, but new technology doesn't always have a direct correlation with better sound. Case-in-point, the prices of 1960s equipment made by H.H. Scott, Harmon Kardon, Marantz and McIntosh all continue to increase from more and more audio enthusiasts desiring the musical qualities inherent from the Golden-era of audio. Granted if you are a purist and want a straight line response curve, these won't scratch that itch, but if you crave a warm musicality MHDT has few peers that can rival.

The Atlantis is one of the latest offerings from MHDT, and much like last generation's Havana, along with the current generation's Stockholm, features a R/2R Multibit DAC. The Stockholm, Atlantis and Pagoda are unique as they have discrete transistors in the I/V stage, no opamps at all. Opamps are often looked down upon as they can be a "one-size-fits-all" type of solution, and the tasks they perform can generally be done better with discrete components. The Atlantis features a AD1862-J DAC chip, and uses a tube-buffered output stage (GE5670).

MHDT Atlantis with stock internals

Luckbad, a member at headphone enthusiast forum HeadFi, created an AWESOME table that compares the more recent MHDT DACs:

Mhdt Labs DAC Families ​
Models​	Havana​	Havana 2​	Stockholm 2​	Atlantis​	Pagoda​	Steeplechase​
Spec
Input Capacity USB (Max)​	16bits/48kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​
Input Capacity SPDIF (Max)​	24bits/96kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​	24bits/192kHz​
Output  Format​	16bits​	16bits​	16bits​	20bits​	24bits​	24bits​
Digital Receiver Chip​	CS8414​	CS8416​	CS8416​	CS8416​	CS8416​	CS8416​
USB Chip​	CM102AS+​	CM6631A​	CM6631A​	CM6631A​	CM6631A​	CM6631A​
DAC Chip​	PCM56P-J​	PCM56P-J​	PCM56P-J​	AD1862-J​	PCM1704​	AK4396​
DAC Chip Construction​	R/2R Multi Bits​	R/2R Multi Bits​	R/2R Multi Bits​	R/2R Multi Bits​	R/2R Multi Bits​	Delta-Sigma 1 Bit​
I/V Stage​	Voltage out  DAC's Internal OPAMP ​		Current Out Discrete Transistors I/V,  No OPAMP, No feedback​			Current Out  AD847AQ as I/V​
Tube Buffer​	Tube Buffer with 5670/2C51 ​
Output level​	2.6V​	2.6V​	3.0V​	3.0V​	3.0V​	2.8V​
Output impedance​	32 ohms​	32 ohms​	32 ohms​	32 ohms​	32 ohms​	32 ohms​
Inputs Available​	3 Inputs -- USB/ RCA/Optic​		4 Inputs -- USB/RCA/BNC/Optic​
USB Input Topology​	USB1.0​	USB2.0​
USB Driver for Win XP/W7/W8​	No Needed​	Yes, Needed​
USB Driver for Linux/Mac​	No Needed​
Dimensions clear (WxDXH) ​	260X150X60​		276 x 150 x 60 mm​
Dimensions w/ socket ​	280X170X60​		295 x 170 x 60 mm​
Weight​	1.8Kg​		2Kg​
Box Color Avialable​	Black Only​		Black/Silver Selectable​			Silver Only ​

It's been fun to see the progression of MHDT DACs over the years. The chassis used to be made completely out of acrylic. Now only the front cover is acrylic (a nice thick acrylic) and the rest of the body is make of aluminum panels that screw together. In addition, the op-amps are going away and there is more utilization of surface mount components on the PCB. The circuit boards have also become more robust, which is nice when exchanging components. Other components generally stay about the same, from Nichicon Fine Gold electrolytic caps in the power supply, Nichicon Muse caps and Sanyo/Panasonic OS-CON caps elsewhere, as well as MHDT brand film caps which I imagine are sourced in Taiwan.

I generally like to replace the Muse caps with Elna Silmic II for a little more warmth, as well as Soniccraft 600v 0.1uf and 0.22uf Sonicaps for the smaller film caps, as Sonicaps are a great value and are small in form factor compared to most other audio capacitors. For the output caps, replacing with the best quality that fits that you can afford is generally the best strategy, as they are directly in the signal path.

MHDT includes a larger toroid in the Stockholm, so I wanted to upgrade the power supply in the Atlantis. I checked Mouser and Digikey for a larger toroid and no one seems to make a unit with the two secondaries needed, so you'd either have to have two toroids (which wouldn't fit in the case) or snag one from MHDT directly. The larger unit from the Stockholm fits perfectly well in the Atlantis, you don't even have to drill a new hole to mount it. While they look similar in size, the larger one is twice the volt-ampere rating.

Comparing the larger toroid from the Stockholm (black) to the stock Atlantis unit (white)

The RCAs on the unit are perfectly fine, but I was able to source some nice ones with teflon insulation, so I installed those. The unit on the left is the teflon insulated one, it looks a little bit different but fits perfectly. 

Teflon RCA left, stock RCA right

The RCA for the digital coax was replaced with a Vampire BNC (about $13-14). I chose Jupiter HT paper in wax caps for the output. They've served me well in other applications and have a nice natural presentation. I happened to have several Kiwame resistors that I ordered from Partsconnexion. 

The Jupiter 2.2uF 600V caps had to be shoehorned to fit. While they fit fine in the Havana (albeit tightly), the Atlantis opening was a little narrower despite the slightly larger chassis footprint. Reviewing my options, I decided to stand the caps off the board slightly to clear the small Oscons and sand down the heatsink to allow the capacitor to wedge up next to it. It doesn't get terribly hot, so we'll see how that goes.

While I don't go out of my way to get audio fuses (I'd be pretty grumpy if a $70 fuse broke, and I'm a little skeptical as the resistance in a fuse is minimal), PCX had a few on sale for $12 from HiFiTuning so I figured I'd give it a shot. $12 is a drop in the bucket for audio gear as you know. Swapping the 400ma stock fuse with the gold fuse seemed to increase the higher frequencies (by a small degree), so it may be counteractive when you're after a warm-sounding DAC. I'll be testing more, but that's my initial finding. I may try in some other equipment to see if that's consistent if they're still cheap for my next order ;).  

Click to zoom in

The DAC sounds excellent. More resolving and clear than my Paradisea and less forward than my Havana. It's my favorite sounding MHDT so far and very easy to listen to. I hear the Stockholm is even better (based on forum banter around the web), but this is a DAC for a few bucks less. 

UPDATE: I found some 30mm aluminum feet with a damping ring on Aliexpress that are a nice step up from the stock plastic feet. They're  quick and easy replacement and are less than $10 for a set of 4.

The Fine Print:

Please remember that modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a posted modification and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. 

Modifying the MHDT Havana DAC

MHDT has a cult following in the DAC world, and for good reason. They may not be featuring all the latest chip designs and 24bit oversampling converters, but new technology doesn't have a direct correlation with better sound. The equipment designed in the 1960s from H.H. Scott, Dynaco, Harmon Kardon, Marantz and McIntosh is still well sought after today for it's excellent sound qualities. Granted if you are a purist and want a straight line response curve, these won't scratch that itch, but if you want to enjoy the music they'll fit the bill perfectly well.

The MHDT Havana comes after the venerable Paradisea 3, which is an excellent sounding example of a NOS (non over-sampling) DAC with a tube buffer. Both the Paradisea and the previous Constantine make use of a Philips TDA 1545A DAC chip and come in a handsome translucent dark acrylic. (See the posts covering the modification of the Constantine and the Paradisea.) Unlike the previous two, the Havana uses no op-amp for I/V conversion. Opamps are often looked down upon as the tasks performed can generally be done better with discrete components. The Havana features a 16 bit R-2R Burr Brown PCM56P DAC, and uses a tube-buffered output stage (GE5670).

A stock MHDT Havana DAC

It's interesting to see the progression of MHDT DACs over the years. Not only are the op-amps going away, there's more aluminum panels and less acrylic body panels, as well as the utilization of more surface mount components on the PCB. The circuit boards have also become more robust, which is nice when exchanging components. Other components generally stay about the same, from Nichicon Fine Gold electrolytic caps in the power supply, Nichicon Muse caps and Sanyo/Panasonic OS-CON caps elsewhere, as well as MHDT brand film caps which I imagine are sourced in Taiwan. 

The stock PCB removed from the chassis

I generally like to replace the Muse caps with Elna Silmic II for a little more warmth, as well as Soniccraft 600v 0.1uf and 0.22uf Sonicaps for the smaller film caps, as Sonicaps are a great value and are small in form factor compared to most other audio capacitors. For the output caps, replacing with the best quality that fits that you can afford is generally the best strategy, as they are directly in the signal path.

Below is a partially modified unit. Note the Nichicon FG power supply smoothing caps have been bumped up to 3,300uF (there's plenty of room), most film caps have been replaced, and I had just started installing the Elma Silmic II caps.

Partially modified PCB, note larger Nichicon FG filter caps, Sonicap film caps

The RCAs on the unit are perfectly fine, but I was able to source some nice ones with teflon insulation, so I installed those. The unit on the left is the teflon insulated one, it looks a little bit different but fits perfectly. 

Teflon RCA left, stock RCA right

The RCA for the digital coax was replaced with a Vampire BNC (about $13-14). I chose Jupiter HT paper in wax caps for the output. They've served me well in other applications and have a nice natural presentation. I happened to have several Kiwame resistors that I installed in the tube buffer. 

The completed mod

The Jupiter 2.2uF 600V caps just narrowly fit in the Havana chassis. I tombstoned one of the Sonicaps to ensure there was enough clearance. One thing I found odd was MHDT never grounds their DACs. I understood there wasn't much of a point with an acrylic chassis, but now that they're brushed aluminum, might as well use it as a shield. The electroplating is very thick on the chassis and needs to be sanded away to make contact. I used a Dremel on the metal under each screw and put everything back together, checking for continuity with a multimeter. I had to re-hit a few of the holes but eventually got there. I ran a wire from the ground on the IEC to circuit ground and connected to chassis ground, so now we have a safe and shielded DAC. 

Boxed back up

Everything is sounding very nice so far. The op-amp-less design is a little more forward than the Paradisea (which is very warm and syrupy), but still very natural sounding and makes for an enjoyable listen. When I say forward, I simply mean related to other MHDT DACs. It's still warm compared to 95% of DACs on the market. I still have to let the Jupiters burn-in, which in my experience just takes a couple of nights of audio running through them, but everything will open up once they do. 

The Fine Print:

Please remember that modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a posted modification and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. 

The Latest Updates - Bottlehead and MHDT

Like an artist may say that a painting is never done, or the guys at PIXAR saying a movie is never finished, some of us electronics nuts feel like a project is never done. There is always another tweak, another piece to be added, substituted or upgraded. In the interest of keeping all information on a particular project in one place, I regularly go back and edit existing posts to include updates.

The first update to cover is the MHDT Constantine NOS DAC. When I was placing an order for some nicer caps in the MHDT Paradisea, I opted to get a few for the older Constantine as well, replacing the four 0.10uF stock caps with Obbligatos. A little bit of drilling of the soldering eyelets was required for the thick leads. Luckily, the Constantine board is one sided and I didn't have to worry about the conductive shells of the Obbligatos touching any traces. I did opt to add Teflon sleeving to the leads so that they wouldn't short across the shell though.

A few more of those beautiful gold Obbligatos for the Constantine

You can find the rest of the story here:
http://www.diyaudioblog.com/2011/02/modifying-mhdt-constantine-nos-dac.html

The second update covers a few additional modifications for the Bottlehead Crack headphone amplifier.  I managed to squeeze in a Solen 220uF film cap in the final electrolytic power cap location, sitting on a pair of standoffs. I also took the time to bypass the other two power caps with a pair of low-cost Audiophiler 2.2uF film caps. A Triad C7X was selected with a rating of 270ohms to take the place of the final resistor in the power supply (also 270 ohms). Since pretty much all the real estate has been used up on the plate, two 2" aluminum standoffs were used to raise the choke above the capacitor near the RCA inputs. This required adding 1" spiked feet to the bottom of the wood base for adequate clearance, just like in the Bottlehead S.E.X. build.  

Large Solen power cap and Triad choke

You can find the rest of the story here:

http://www.diyaudioblog.com/2011/02/bottlehead-crack-otl-headphone.html

Finally, just a few days ago a MHDT Paradisea NOS DAC modification project was finished up. A variety of nice items were installed including Takman and Kiwame carbon film resistors along with Obbligato and Mundorf Silver Oil film capacitors. Next on the list for this mod is a Burr Brown op-amp to replace the stock Analog Devices one. 

Some creative mounting of the Mundorf Silve Oil Caps

You can see the whole story here:

http://www.diyaudioblog.com/2011/05/modifying-mhdt-paradisea-nos-dac.html  

Be sure to keep an eye out on other posts for new updates. I hope to be finishing up the Millett Jonokuchi headphone amplifier in the next few weeks, along with casing up a completed AMB Mini Cubed portable headphone amplifier. Of course it will be unique looking like my other projects ;)

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a modification posted below and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.