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. 

Modifying the MHDT Paradisea NOS DAC

The MHDT Paradisea is an excellent sounding example of a NOS (non over-sampling) tube DAC. If you're not already familiar with MHDT's offerings or the concept of a NOS DAC, I encourage you to read through my post regarding the modification of the MHDT Constantine DAC. Both of the units make use of a Philips TDA 1545A DAC chip and come in a handsome translucent dark acrylic.

The main difference between the two units is the 5670 tube buffer, which is directly coupled to the op-amp. Per the Enjoy the Music review of the Paradisea, various tube equivalents can be substituted, such as the 2C51, Western Electric 396A, 6N3Pi (6H3pi), or the 6CC42. I have yet to experiment much with tube rolling on the unit, but the example here came with a Western Electric 396A. Visibly, there are quite a few more parts in the Paradisea, and MHDT appears to have used mostly Nichicon MUSE electrolytics versus the Elna Silmics in the Constantine. The Paradisea also contains a torroid rather than a flat-pack transformer, it appears that MHDT has switched their entire line to torroids now, so I'd imagine this difference is indicative of the vintage of the unit. 


Of course the unit was going to be going under the knife, but I wanted to identify my purpose for doing so. When I first plugged in the Paradisea, I immediately noticed a more crisp and detailed presentation as compared to the Constantine. While the added detail is nice, the treble energy may be just a tad much for those of us with sensitive ears. Taking a look at the parts inside, every resistor was blue, which in nearly all cases means that they are metal film. Carbon film resistors typically are a tan color, of course when it comes to boutique resistors, vendors color them whatever they like (pink Takmans, green Kiwames, red PRPs, etc.).

The reason this makes a difference is that carbon films generally have a slightly warmer and more natural sound compared to the more detailed sound of metal film. The vast majority of new equipment makes use of metal film as it's very easy and cheap to get values within 1%. Carbon film is more typically found in vintage equipment, along with the slightly sweeter sounding carbon comp resistors. People tend to stray away from carbon composition these days (except for grid stoppers) as they pick up a little more noise and can drift over time, but they do have a nice sound and can be used as long as you are mindful of their shortcomings. Because I'm more fond of the sound characteristics of carbon film versus metal film, I decided that I wanted to replace as many metal film resistors as I could from the Paradisea. 

The original MHDT Paradisea with the top off

Resistors cannot be measured reliably when within a circuit, they need to be removed to be measured or you can read the color stripes on the resistor, although this can sometimes be difficult to determine a color (orange versus red, white versus gray) on a minuscule resistor. In most cases, I removed the resistor to measure it, wrote down the value and position, and only if it was a strange 1% value I put it back. Any other resistors that visibly matched these values were not removed. Common values were replaced with a combination of Kiwame (Koa Spears) and Takman resistors, the Kiwame leads needing a little bit of filing to fit. Some 1% uncommon values were replaced with generic 5% carbon films; I basically purchased large amounts of close values and measured them, picking out the ones that measured within 1% of the color code on the original resistor. It's a very slow and regimented process, but is enjoyable if you like working on electronics ;) 

Modifications in progress

The MHDT units come with some very nice parts for sure, but there can always be room for minor improvements. I opted to replace the stock film caps, which are relatively small compared to other caps of the same value. Based on dimensions, Auricaps, Obbligatos or ClarityCaps would be the closest match, all being a little bit larger. I selected Obbligatos as they tend to be fairly neutral and are a nice price for what you get. The problem with Obbligatos is their attractive gold shell is conductive, so when the leads are bent around the bottom or the cap is sitting on solder eyelets, the shell will short them. I usually put some 3:1 clear heatshrink over top to prevent this from happening. 

Clear heatshrink over top of the Obbligato cap

Heatshrink shrunk to fit

For the output caps, which is a very audible position for capacitors, I selected a matched pair of 2.2uF Mundorf Silver in Oil. These are quite large, with thick leads, so some creative mounting was required. The solder eyelets for the capacitor leads had to be enlarged with a 1/16 drill bit, and one of the caps actually sits outside of the unit for a very hot rodded look :) When solder eyelets are drilled, it effectively separates the conductivity from the top and the bottom of the board, so in some circumstances, depending on whether the copper traces on the PCB run along the top or the bottom, you have to solder not only to the bottom but the top of the board as well. 

Finished PCB - front view

Finished PCB - rear view

I opted to cover the leads of the right channel Mundorf capacitor with teflon, then sleeve them with black nylon as they would be visible from outside of the unit and needed to look nice. 

Finished mod, PCB in case with top off

Completed Modified Paradisea

The Paradisea now has a more warm, natural sound with slightly more bass quantity (while still being very controlled). Midrange seems to be more liquid and smooth. Overall, I'm very happy with the presentation. Now for some tube and opamp rolling! :) 


UPDATE (6/11/11): The Paradisea is made for op-amp rolling (pulling out the stock operational amplifier and putting a similarly spec'd one into the gold 8 pin socket). I dropped in a vintage NOS Tung Sol 2C51 tube and a Texas Instruments OPA2107AP op-amp in the unit. Immediately noticeable was a big bump in upper-end clarity and detail. I'll need to spend some time with the unit to see if this is preferable to the stock op-amp with Western Electric 396A or not (verify if this new-found detail is fatiguing at all over long periods).

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. Please keep this in mind.  

Modifying the MHDT Constantine NOS DAC

Choosing a DAC (Digital Audio Converter) is a lot like choosing a car; there are a tons of options out there, but there are only a niche few that best suit your preferences and personality. After sampling quite a few DACs at various meets, I've found that I personally prefer NOS DACs. NOS means non over-sampling. I feel that they generally exhibit a fairly smooth and musical character and are non-fatiguing. Some people relate the sound to an analog record versus a digital CD. If you are after a quick, precise and analytical sounding DAC, then these aren't for you ;)

There are a number of NOS DACs on the market, including offerings from Scott Nixon, Ack! Industries, Teradak Audio, MHDT Labs, Lavry, DIY Paradise, Pacific Valve and others. I would argue that the Taiwanese company MHDT is one of the most well known makers of NOS DACs. They've offered a number of different levels of DACs, including the Digital Renaissance, Constantine, Paradisea and Havana, some with tubes, some without.

The MHDT Constantine is solid state, meaning it doesn't include tubes, and is an excellent value if you can find one on Audiogon. They typically sell used for $200-250 and would make an excellent introduction to non-oversampling DACs. With a few tweaks, I was able to eek out a little bit more detail while maintaining the same character of the DAC.

Original MHDT Constantine - Click to Enlarge

Modified MHDT Constantine - Click to Enlarge

There are a few slots on the board for film bypass caps that hadn't been taken advantage of, so Sonicaps were used, along with a couple other places where they would fit. Two of the original Elna Silmic caps were in the way of the capacitors, so they had to be removed and replaced with longer legged Silmics (with teflon tubing preventing any shorts). The BNC was replaced with a Vampire BNC and the output caps were swapped in favor of gold Obbligatos. Both the Sonicaps and Obbligatos are well known values in the world of film caps. You'll find a rundown here on the famous Humble Homemade HiFi Capacitor Test.

UPDATE (5/16/2011): While I was modding my MHDT Paradisea, I decided to go ahead and replace the four 0.10uF stock caps in the Constantine 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.

Newly added Obbligato caps

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. Please keep this in mind.