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.