ALO Audio Continental Dual Mono Dac/Amp

General Information

The ALO Continental Dual Mono

From ALO:" When we started working on our newest generation Continental wanted to do something amazing. We examined each element of the amplifier - 6111 tubes, Wolfson DAC, Power Supply, Volume Potentiometer, Battery, Capacitors - to find the best sounding component. As we put them all together we ended up with The Continental Dual Mono. "

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100+ Head-Fier
Pros: Portability (kind-of?), overall superb sound quality, ability to tube-roll
Cons: Limited to DSD 64, runs hot, sub-par battery life, could be more transparent
The last time I bought a product from ALO Audio was 4 years ago. It was the National. Before that, I had also bought a Continental V2, which was a very popular portable tube amp back in the days, often stacked together with a Cypher Labs AlgoRhythm Solo and an iPod Classic

To be honest, I didn't like them that much. Looking back now the reason is even more obvious: ALO's products back in the days either sound too harsh in their solid state amps or too "meh" in their tube amps. Paired with the AlgoRhythm Solo, they were even worse, as the Solo wasn't a very musical portable DAC back in the days. So I didn't expect much from ALO Audio for the last 4 years, even going as far as ignoring their products from my wish list.


The Continental Dual-Mono (CDM) changed my mind though.

First things first, this piece of brick is definitely overpriced as *explicit*. 200,000+ Yen for a new CDM here in Japan. That's Chord Hugo-level expensive. I would expect a portable product to be around the level of the 100,000 ~ 150,000 Yen price range, so this was a shocker. It's not to say this is so much worse than the Hugo that I'm deeming CDM unworthy of its price point, but with Hugo being so revolutionary in its FPGA technology, it's almost impossible for me to justify CDM's asking price.


Price aside and the well-documented heat issue aside, this is a winner, IMO. To simply put it, the CDM is an average DAC paired with a very good amp. I'm very disappointed that it does not do anything beyond DSD 64, rendering most of my SACD-rips useless unless down-sampled. I'm also disappointed in the DAC's lack of transparency and musicality in comparison to Chord's Hugo (and even the Mojo). The Wolfson chip inside does its job alright, though, sounding well balanced without being harsh to my ears. I don't have the most accurate ears, but I'm guessing it was designed along with the amp to be rolled-off in the highs. I would have liked a little bit more treble detail and extension, but that's nitpicking. Again, it does it job as a DAC.

CDM's amp section is where it really shines. As a hybrid amp, it doesn't have the stone-cold harshness of a solid-state but certianly retains a solid-state's neutrality. Nothing is really distorted beyond crazy levels, but I can definitely hear the tube-ness of it in its gentle highs and that natural yet authoritative bass response.
In comparison to Hugo and Mojo's amp, CDM is more powerful in the sense that it drives my Focal Elear and HiFiMAN Edition X V2 with much better dynamics and punch. On paper the CDM is weaker than both the Hugo and the Mojo in terms of measured output, but trust me here, you'll hear a wider sound stage and a livelier sound with the CDM. I'll also add this is without sounding "fake" or harsh, too. 

Hugo, on the other than, is more transparent, more detailed, and retains more of that sparkle-goodness in the treble department.

Quite surprisingly, I would not consider the CDM as having a "warm" sound. This is an amp with a neutral sound signature to my ears. I would only characterize it being south of neutral when being compared to Chord's products, but again, nothing is too distorted or too warm.

Funny thing is, remember how I said the CDM drives my headphones better than my Hugo? Well after extended period of time listening and cross-pairing, I do find that the CDM have better synergy with low-impedence headphones and IEMs (JH Audio Michelle, Sony MDR-EX1000 etc.) than the Hugo. But when it comes to mid-to-high level impedence headphones such as the Sennheiser HD600/HD650 or even some planar magnetic headphones, Hugo comes out as sounding more natural, driving them with better ease.

After moving away from iPods and into other DAPs in the past two years, I have become a supporter of high resolution music formats. Listening 24/96kHz and DSDis the way to go, IMO. So I must say, again, I'm super disappointed in that the CDM only supports as hi-res a format as DSD 64.

(Note: DoP or Native doesn't really matter to me)

[size=15.2px]Overall, I think it's a heck of a [size=15.2px]DAC[/size]/AMP combo. Not quite Hugo-level high-end-like sound quality, but certainly a winner among the others I have compared it to.[/size]

[size=15.2px]I actually prefer the CDM over the Hugo when I'm listening to larger orchestral works or pop music. Also, I would like to add that CDM sounds smoother to my ears when used as a [size=15.2px]DAC[/size]/AMP instead of just an amp. Granted, it will get very hot quickly as a [size=15.2px]DAC[/size]/AMP, but in order to get the sound I like, I'm willing to deal with some annoying quirks :wink:[/size]

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Headphoneus Supremus
Pros: see review
Cons: see review
Warm signature will pair well with many IEMs/headphones
Lush midrange
Tight bass
Dynamism without harshness
Tough construction
Emotive: breathes life into music
Custom PCB attachment method
Could be keep you from freezing to death if your car broke down during winter in the middle of nowhere
Runs hot
Moderate battery life
Limited to DSD64 and below
Lack of optical input (for users of AK and similar devices)
Gain & input selector switches protrude from chassis, reducing portability options
EMI/RF interference
Review Contents:
    Reviewer Introduction
    Product Introduction
Technical Specifications
Under The Hood
Review Approach
Hands On/Operation/Aesthetics
Sound Quality
    Sound Stage
Suggestions For Improvement
Reviewer Introduction
          I am both a stereophile and an audiophile.  I am an audiophile so as to further my enjoyment of the music I consider essential in life.  Life without music isn’t much life at all, when I’m able to hear details I couldn’t hear before in a song I’ve heard hundreds of times or when the song is brought to life even more via better reproduction the reason for seeking out exceptional audiophile gear becomes self-evident.
          A big THANK YOU goes out to @canyon-runner for lending me the ALO CDM.
Product Introduction
          The CDM is a unique collaboration between Ken Ball and Vinnie Rossi.  It’s a class AB tube and solid state hybrid DAC/amp, per Vinnie:
“As far as I know, the CDM is the only portable tube based amp/converter which is all linear voltage regulated.  Also worth noting is that we decided to keep the volume control in the analog domain, using higher quality conductive plastic potentiometer instead of the more common carbon tracker.”
          The ALO website ( summarizes the device:
“The Continental Dual Mono…delivers the low output impedance, tight bass and sonic precision of a solid-stage amp…with the added midrange richness, expanded soundstage and spaciousness of a tube amp.”
          Both men are well respected in the audiophile community; Vinnie being the amp, cable and source mod extraordinaire and Ken being a cutting edge innovator in the amp space.
Peering through the Gorilla Glass you’ll find dual class A mechanically isolated auto-biased Sylvania 6111WA tubes attached via Ken’s custom PCB.  Changing tubes is easy due to Ken’s system, just make sure you are installing the tubes on the CORRECT side otherwise you can damage your CDM.  Please see Ken’s video on swapping out tubes (  Various tubes can be purchased on the ALO website.  Ken says you should get 5+ years of use out of set of tubes.  Their design uses the tubes as a current buffer, supplying the current gain to the amplification resulting in a “clean, strong and dynamic signal”.  In amp only mode only one channel is used but both tubes remain powered, hence the “dual-mono” monniker.
          A Wolfson 8741 DAC chip is used for digital processing and a Cmedia USB receiver chip processes micro USB input.  According to Ken he chose the Wolfson 8741 because it had a very low signal-to-noise ratio, low distortion, low noise, superior linearity and an extended dynamic range.  Independent internal voltage stages (a linear voltage regulator is allotted to each stage) reduce voltage sharing and crosstalk across the various stages which allows for reduced output noise and cleaner amplification.  The left and right signals are independent of each other with regard to amplification.  The CDM can handle data up to DSD64.  An led light system indicates sample rate:

Red = 44.1, 48kHz,
Green = 88.2, 96kHz,
Blue = 176.4, 192kHz,
White = DSD​

          The CDM is a jack-of-all trades (minus optical).  It features a 2.5 balanced input/output (has lower IMD/THD/crosstalk than the other ports), microUSB to DAC, 3.5mm stereo and a 3.5mm line out.  A lo/hi gain switch and a load that is handled by class A/B transistors ensures your entire inventory from extremely sensitive IEMs to power hungry cans will be fed properly.  The CDM features 3x18650 batteries joined together in circuit.  They are high quality batteries, the same Panasonic 18650’s many flashlight enthusiast like myself use and also the same batteries Tesla uses in their vehicles.  The button top protection on each battery prevents these powerful batteries from exploding as a result of over or under charging.  The battery back can be popped out and replaced with a new one if you find you aren’t getting good battery life after years of use with the CDM.  As long as you can plug into the wall you can rock on.  Micro drilled vent holes dot the CNC’d aluminum chassis.  The unit is easy to tear down with a 1.5mm hex key.  Finish options include black or silver.  When Ken & Vinnie designed the CDM they wanted to “…do something amazing.”  Did they or is your money better spent elsewhere?  Read on to find out.
Technical Specifications
Important Internals:​
Wolfson 8741 DAC
2x Sylvania 6111WA Tubes
3x18650 – Panasonic 18650’s w/protection
Cmedia USB Receiver​
RMS Per channel, both channels driven:​
Single Ended
80mW - 32ohms
95mW - 50ohms
75mW - 150ohms
60mW - 300ohms​
125mW - 30ohms
145mW - 50ohms
110mW - 150ohms
95mW - 300ohms​

Input Impedance Single Ended is 10k
Input Impedance Balanced is 50k
Output both modes is less than 1 ohm​
Under The Hood
Review Approach
          I paired the CDM with my 16 ohm ADEL A12 CIEMs.  I used the Chord Mojo with both my 2011 Macbook Pro & S7 Edge, both in DAC/amp and amp only modes.  The A12’s are warm and dark with recessed highs, powerful sub bass and bumped mid bass.  There are removable modules available for ADEL compatible CIEMs (, for this review I will be using the manually adjustable module (MAM) at the ¼ turn from fully open setting and the B1 module.  I had the CDM for approximately three weeks, listening to it every day for 8-10 hours.
          The CDM is well protected in its’ thick walled minimalistic cardboard box and grey foam cutout cushion.  A small drawstring bag contains several elastic bands for stacking, a European style wall plug and a USB cable.  Also included is a typical cabled American plug wall charger and a small instruction manual.  
Hands On Operation/Aesthetics
          I get the same feeling of extreme quality I got from holding the Chord Mojo when I hold the CDM. It’s hefty.  All the words found on the device are engraved.  The finish is top notch.  The ports are all nearly flush with the body.  A s mall rotation of the potentiometer turns the unit on while dual LED’s indicating battery state and sample rate flank either side of knob.  The LED’s accurately displayed the sample rate as I cycled through DSD64 to MP3 on my Macbook using Jriver Media Center.  The potentiometer knob is grippy allowing for miniscule adjustments.  Unfortunately the gain and input switches protrude quite far from the chassis, making only a flat lay possible and restricting portable options.  The switches produce a reassuring click and feel solid.
          The CDM weighs approximately 15 ounces.  It’s about 5.7” long, approximately 3.2” wide and 1” thick.  The unit gets very hot very quickly, more so in microUSB fed DAC mode as opposed to Amp only mode.  High quality batteries reassure the user that the CDM can handle the higher temperatures and the vent holes do well to dissipate heat.  Putting it in a pocket or bag isn’t a good idea as it will get even hotter.  I have found it most convenient to use it unstacked on my desk.  With my laser thermometer I measured ~118F while running in DAC mode and charging at the same time for several hours.  The batteries deplete faster in DAC mode.  The DAC will not receive power unless a microUSB cable is plugged in.  I averaged about 6.5 hours from a full charge with time split between amp only and amp/DAC modes.
          I get more than enough volume with my ADEL A12’s on low gain.  I can’t imagine the CDM not being able to provide enough dB to any CIEM.  I did experience moderate EMI/RF interference with my S7 Edge, to eliminate it I used airplane mode.  To further eliminate EMI/RF I use ferrite devise in my microUSB-microUSB OTG cables.  I experienced no EMI/RF when using my Macbook Pro with the CDM and my S7 Edge was nearby.  I experienced no hiss on lo gain with my A12’s.
I had no serious issues getting the CDM setup, I did have to download a driver pack for my Mac:  I had no issues when sync’ing the CDM with my S7 Edge using a startech microUSB to microUSB OTG cable.
Sound Quality

          The CDM does a great job of creating a warm signature without sacrificing resolution and detail.  You get the tonality you expect from a high quality tube system without losing accuracy while simultaneously having the precision, tightness and black background of a solid state system-remarkable.  It takes the middle road between high resolution and a transparent musical experience, walking the tightrope perfectly.
          Everything sounds more alive with the CDM.  I can’t help but think of a warm fire, dancing on a cold winter night on one of my solitary winter hiking trips: comforting, warm and alive.  Listening to Chord Mojo now without the CDM, it sounds thin and dull.  The CDM breathes life into the music, infusing it with a warm dynamism that increases contrast between frequencies yet remains smooth and not harsh.  This life-energy that the CDM brings to the song is what I will miss most when I have to send it back to @canyon-runner and it’s likely I’ll to buy one myself someday because of this.    
Fed digitally via microUSB (DAC mode) there is a slight softening of the sound, a miniscule recessing of the high’s, increased bass quantity and increased separation between highs and lows, due to this I hear slightly less resolution when the CDM is fed a digital as opposed to a high quality analog signal form a top shelf DAC.  To extract the highest sound quality from the CDM you need to supply with a high quality analog signal from a powerful DAC.  In either mode I experience incredible separation, imaging, soundstage size/accuracy and immense micro detail pulling together into a lush cohesive and transparent whole.
          The stage of the CDM is much larger than that of my Mojo.  Width of the stage is the most noticeable aspect of the CDM’s soundstage presentation.  Mojo gave me the effect of hearing the cash registers in Pink Floyd’s Money as being an inch or two outside my CIEMs, the CDM increases this distance while allowing placement of the instrument in the stage to be more precise.  Floor space between the musicians on stage has increased and as such a more accurate stage is created-call it stage resolution.  Vertical height exceeds Mojo and is present across my head from left to right.  Depth is on par with Mojo, revealing layers of a song as individual yet part of the coherent whole.
          In amp mode and fed with an analog bitperfect signal from S7 Edge/Macbook -> Mojo -> CDM, this is the most resolution I have ever heard.  Details are more discernable due to the increased high and mid high presence from the CDM(remember my A12’s are rather dark and very warm).  The CDM does a fantastic job contrasting the highs from the lows, the mid-highs from the mid-lows and as a result you get this incredibly detailed output-especially when an analog input is used.  Micro details about and I couldn’t be happier with the resolution in amp mode.  When using DAC mode from my S7 Edge or Macbook Pro (bitperfect signal from both sources) I notice ever so slightly less detail than when running amp only mode with my Mojo.  This is due to the gently rolled off highs and slightly increased bass in microUSB mode.  The difference is pretty small and unless you were actively looking for it I doubt you’d notice it, but it is there for those of you who are willing to stare keenly into the sonic abyss.   
          Every time I listen to the CDM I find everything else disappearing and only the experience of the music remaining.  On many occasions I was listening to Bandcamp with the intent of wish listing albums I liked for future reference as I went along.  Several hours into the session I’d forgotten to wish list anything having heard many excellent songs.  The emotive, warm and alive signature of the CDM draws me in and sweeps me away every time.  It pulls me into the music and into the moment.  I experienced none of the pop’s, chirps or other issues that can often occur with tube systems.  I did experience EMI/RF when using the CDM with my phone but it was easy enough to simply switch on airplane mode to completely eliminate it, ferrites attached to the cable also lowered the volume on the interference.  When using my Macbook Pro as source with my S7 Edge about 2 feet away, I experienced no EMI/RF interference.  

          The CDM presents the mid-highs and highs exceptionally well.  I’ve never heard the pin point stage accuracy I hear from the CDM with regard to the highs.  Cymbals are placed accurately in stage, whether that be above and to the left, below and to the left, etc.  Finally I hear the twinkle/sparkle I’ve always wanted from my dark A12’s.  Helping this effect is the aforementioned contrast the CDM renders between the frequencies.  Extension is above average.  It’s twinkle without harshness or an unnatural roll off or recession.  Spikes are non-existent, high notes let you know they’ve entered the stage but they don’t stand out apart from the rest of the presentation-the transparency is preserved.  Micro detail is very good, probably good enough to satisfy most detail fanatics.
          It would be a tossup between soundstage and mids as to which is the strongest hand the CDM plays, both are exceptional.  The mids are lush, elevated, warm, incredibly detailed and smooth.  The balancing act between a warm smooth signature and micro details is performed flawlessly in this frequency spectrum.  Mids are full and slightly forward but in no way does mid bass bleed into the other frequencies, the decay is minimal due to the solid state attributes of the CDM. Timbre is ideal being neither overly musical nor harsh-a very transparent experience.  I detected no sibilance at all from the CDM even when tested with female vocals that are known to be sibilant.  Male vocals sound spectactular.  Take Matt Hyde from Beastwars, he sounds even more like he’s in the room with me.  His voice is more fleshed out, more present, and powerful.  The best qualities of vocalists are amplified.  No matter if it’s a male or female voice, the CDM renders voices with more stage presence and more life.  The mid presentation is very easy on the ears, lending to a fatigue free experience although I’ll admit I haven’t felt fatigue since switching to monitors with ADEL technology.  
          The lows-and the timbre-are where you can hear most that the solid state portion of the CDM is in play.  Both the mid and sub bass are energetic, bold, tight and punchy.  They enter the stage with authority and decay quickly allowing for more accuracy in the mid and sub bass presentation.  Extension is low and deep enough for my tastes.  The characteristic warmth and fuzz a tube creates is alive and well in the CDM but it does not distort micro or macro details to a noticeable degree.  The CDM wraps you up in it’s warmth, it’s an enveloping energy and something my Mojo can’t do on it’s own and it’s one of the reasons I enjoy the CDM so much.   
Suggestions For Improvement
          Use flush or barely protruding switches on the chassis and make an Amp only version of the CDM as many of us already have excellent DAC's.  I would love to see a cheaper version of the CDM minus DAC mode, it would be amazing if it were under $1,000 and I'm sure it would sell fantastic as long as the output sounded exactly the same as the CDM sounds now.
          It’s a pretty safe bet that the CDM will pair very well with most any headphones/IEMs you own.  With it’s warm enveloping sound, great detail, no harshness, excellent dynamism and contrast, massive soundstage, tight and authoritative bass decay, fast timbre, inky black solid state background, a lush sibilance free midrange and smooth sparkly highs you'll be in audiophile nirvana in no time.  It does get hot so don’t stuff it in a bag.  Two of the switches stick out far and render many portable modes of carry impossible because one would be positioning the CDM with it’s weight on those switches in many instances and I wouldn’t do that to the CDM.  Runtime is good, expect approximately six hours from a single charge.  Charging while playing means you never run out of music so long as you can plug into a wall outlet.  The price is high but when you consider the quality of the parts and the sound quality I find it on par with other top shelf audio gear.  The battery and tubes are both serviceable by the consumer without too much headache.  Tubes are plug and play so long as the tubes utilize Ken’s custom time saving attachment method. There’s no optical input but I do not need it as I don’t use optical connections.  DSD64 is the quality limit but not an issue for me since having heard DSD many time’s on a competent system I would agree with Rob Watt’s of Chord that it sounds flat and lifeless and I prefer FLAC.  EMI/RF interference will happen with a smartphone not in airplane mode, I experienced none with my Macbook.  
          The CDM is an absolutely incredible piece of audio gear, I will miss it when I give it back to @Canyon-Runner.  The CDM is well worth the price and I know you’ll be very impressed with the sound quality it produces.
forgot to mention one thing; I had ALO put the Sonotone single ended triodes in, and apparently they run just a bit less hot than the stock tubes-and, although I dont personally have a comparison, I hear people like the sound a bit better too...just FYI
Thanks for your comments!
One of the most thorough reviews on HeadFi. Thanks Ike! Time to hit the classifieds!


Headphoneus Supremus
Pros: Sound quality, flexibility, warm tube sound, tube-rolling, portability
Cons: Sensitive to interference, runs hot, higher price-tag (but worth it)
Let’s get something out of the way first. You might be saying something like “Another 5-star review? Seriously? Does this guy ever give anything but 5-stars? Is this dude on happy pills or something? Geez Louise…” Guilty as charged. Another review, 5 more stars given to another piece of Head-Fi gear. Why? So here’s the skinny (and the reason I don’t write for anyone but myself) – I only invest the time (which is non-trivial) in writing these reviews for gear I feel incredibly strongly about. And as an optimistic person I tend to feel the most for things I love. So yes, I tend to write mostly 5-star stuff. Will this always be the case? Who knows, but for now it is. Also I only write a handful of reviews but I (luckily) get listen to and play with a bunch of gear. Okay, now onto the reason we are here, the review of the CDM.
Actually, let’s pause another second first. In writing this review I had a bit of an observation/inspiration, which is included towards the end of what surely is going to be yet another very long review. So if you’re not all that interested in the CDM review but you want to read a bit about my “observation” (dare I say a new “law of HF audio”?) jump down to the part that starts with “***” (it’s easy to search for this string) and see what you think. Now, back to the regularly schedule review, I promise this time!
So after buying and reviewing the ALO Rx ( and getting to know Ken Ball, the main-man behind the magic at Portland, Oregon based ALO Audio, I had the chance to try out his other new headphone amp, the Continental Dual Mono (or “CDM” as its friends call it). The CDM can be thought of as the big brother to the Rx, sharing a similar design philosophy, aesthetic and to some degree sound signature. However, when you pull out the birth certificates and compare them you will see that they’re more like half-brothers for a number of reasons, including: 1) there are two fathers to the CDM, both Ken Ball and Vinnie Rossi (who tag-teamed on its design), 2) they have different amplification lineage, with the Rx running solid state while the CDM utilizes tubes (as would befit an “older” brother), 3) the CDM has more tricks up its sleeve in being able to power both full-sized and sensitive IEM’s as well as acting as both a DAC and amp, and 4) the CDM lives in a richer neighborhood, coming in at $1,495 USD to the little brothers $299. So actually, when you look at it they’re quite different – something along the lines of ‘brothers from another mother’. But Dad had a strong blood-line when it came to his external appearance, and you’ll see the similarities in the Rx and CDM casework.
So let’s cut to the chase. Is the CDM a worthy big brother to the CDM? Will the family be happy when it shows up to Thanksgiving dinner with a “hot” date? (Sorry for the pun, the meaning of which will become clear later.) The answer is “damn-straight” – if the CDM was my brother I’d roll out the red carpet for him (good thing I only have sisters so I should be safe in making this statement) and pour him a nice glass of 30 year old single malt. This is one amazing piece of gear. Is it worth the ~5x price-tag? Again I would answer in the affirmative. For all that it can do, and how well it does it, the CDM is IMHO an amazing value. For while I said in my other ALO review that the “Rx is clearly not a Swiss-Army type of amp” the CDM actually is. Amazing tube amp? Check. Rock-solid DAC section as well? Check. Portability? Most of a check. Ability to power all sized cans? Check (at least for my transducers, with the Noble K10’s and the Audeze LCD-3’s monopolizing most of my listening time). And the CDM is clearly a sexy beast, with almost everyone I’ve shown it to in person saying “Wow!” when they first see it. I’ve also had a number of people ask me “what’s that?” when I’ve been using it on planes or trains. In fact one person who asked me about it turned out to be a potential client – so the CDM is a good business development tool as well!
More details you say? Okay, we’re getting there. First of all (my first minor gripe) the setup process was a bit of a bitch in getting my computer to recognize the CDM. However, I blame that more on CMedia than ALO. Turns out I had to do some updating of drivers and also removal of other DAC’s drivers (which also used CMedia) in order to get it working. And actually in full transparency the issues with the PC are the reason I have my CDM. I got a random call from Ken asking if I was a PC user (clearly they’re more MAC than PC’s guys out in the Pacific Northwest, with I guess is a bit ironic given the proximity of Redmond versus Cupertino, but we’ll save that discussion for another time). I have to admit I felt a bit awkward in answering “yes, I still use a PC”. It was kind of like admitting that you were one of the AV-nerds in school who the teachers called on to get their gear working (I have a sneaky suspicion there might be more than one of us here at HF with that background, right Brian?). Ken asked if I would be willing to help trouble-shoot and write some of the user’s guide/FAQ stuff for the CDM, and after having heard the CDM prototype at CanJam SoCal I was like “heck yeah!”. And without any pre-arranged agreement, and with no strings attached, Ken (who’s a total mensch by the way) told me after all was said and done with the work I had volunteered to do to keep the CDM in recognition for the time I invested in helping get the CDM up to speed.
So now that the PC and the CDM were talking, we were off to the races, and the CDM was hot out of the gates. Yes, hot. The CDM is hot stuff, literally and figuratively – like Shannon Elizabeth in American Pie (sorry, I have to put in a movie reference every paragraph or two). This tube powered unit sure pumps out some thermal energy – even the volume knob gets pretty warm! I recommend picking the CDM up by the sides around the vent holes, which by design stay cooler. I’d guess from touch (I actually used to have my touch calibrated to temperatures – the fun stuff you learn working in a chemical plant) that it gets up to around 140F maximum, which I think is similar to what Ken measured. Some can hold onto something this hot for a number of seconds, while others will find it hard to even touch for all but the shortest times. This CDM gets hottest in my experience on the part of the chassis between the window and the volume knob, and gets the hottest when you are playing the CDM while it is plugged in to the wall charger and also are using it for both DAC and amp duties. This heat also makes the vent holes very important – so my advice is not to throw the CDM into a bag or pack – let it breathe man! However, once you are aware of it and get used to the heat I didn’t find it to be an issue.
How do you tame the heat? Well, as I already said you keep it well ventilated. And you can also try changing out the tubes. Yes, this bad-boy is on a roll, a tube-roll that is. With the purposeful design the two tubes in the CDM are easy enough to swap out. One Allen wrench, some static dissipation and a few minutes of your time and you can significantly change not only the heat-generation of the CDM but more importantly its sound signature. First the heat. The “pencil tubes” that the CDM uses come in two different types – single and dual triodes. What does that mean? Google it if you want details, but essentially the duals can do stereo duty, handling two signals at once, while the singles are well, just single. Since it is a dual-mono design (the “DM” in CDM) the amp only uses one channel, but has to power both sides of the tube, even the one not being used. So more power equals more heat, oh and less battery life as well. So there is benefit to the single triodes, although you do have to be careful when installing them as the green-PCB boarded single-triodes are chiral, which is chemistry-speak for they have right-and left-sided versions. So be very careful when you’re installing them to put them on the correct side of the CDM or else bad things can happen (I’ve heard of one Head-Fier who already made this mistake and ended up doing some damage to their CDM). To play it safe be sure to watch Ken’s video on how to swap tubes in and out of the CDM, which can be found on the ALO site ( Oh, and two more hints – 1) getting the volume knob off the first time can be a challenge. It can get a little stuck, even after loosening the nut, so just give it a little extra “oomph” the first time after you’ve unscrewed it, and 2) there are little squares of tape holding the back sides of the tubes to the PCB (nothing worse than tape stuck on your backside!), so be careful and apply constant pressure on the tubes after you’ve disconnected the ports to the PCB and the tape will let go. After the first time it’s all easy-peasy.
So what are my thoughts on the different tubes regarding sound? Well our friend Lieven wrote an in-depth CDM tube-rolling review on Headfonia recently which I will point you towards here ( as he did a really great job on it. I’ve only tried three tubes so far, but they are three of the biggies, and the first three in his review – the stock Sylvania 6111’s, the Mullard 6112’s and the Sonotone 5719’s. First, the stock NOS Sylvania 6111’s are a very solid and well-rounded performer (and easier to source) hence why Ken includes them with each CDM. I could have been happy with just leaving them in the CDM and going on with my business, but hey, this thing is built for rolling and who am I to stand in the way of progress? The Mullard 6112’s are IMO simply amazing – the clear choice for wonderful, tube-typical warmth and emotion. Sucky part is that they cost quite a bit more and are very hard to source, so they’re not often available. If you get the chance I highly recommend you pick them up. So my thoughts on those two tube-types (try saying that five times fast!) match with Lieven’s take. Where we diverge somewhat is on the Sonotone 5719 single triodes. I found the 5719’s to be a bit thinner and not quite as engaging, especially compared to the Mullards. However, YMMV, and the 5719’s do run cooler, so they are worth trying out. Now with the Mullards in place I feel like I don’t have to do a lot of swapping around. Whew, at least that’s one element off the audiophile merry-go-round (at least for now!).
“Damn it man, you haven’t talked about how the flippin’ thing sounds yet! Get on with it already!”
Okay, okay – I get the hint. Let’s talk about the all-important SQ. First the soundstage is wider and taller than the Rx – although their depth is similar to my ear. The CDM provides clearly the best soundstage I’ve heard my K10’s throw that I can remember. For example on Eiji Oue’s amazingly recorded “Reveries” the haunting “Gymnopedie No. 1” is broad and nuanced at the same time, with the clarinet solo seeming to hang in space, suspended by who knows what. On R.E.M.’s “Laughing” from “Murmur” the bass has real depth while the symbols seem to sprout out of your ears and eyebrows like the errant hairs on a mad-scientist. This is good stuff.
Like well-designed tube gear the CDM allows you to see the delicate nature of instrument images. It’s not that you’re overtaken by additional detail, which there certainly is, but rather the way the details and instruments are portrayed that is so impactful. It’s like looking a painting by a master and realizing that while the overall image is stunning, that the fine brushwork is so nuanced and refined and that this extra texture makes the whole picture better. The delicate nature of the note is delivered with great power where needed. It’s like switching between a compound bow and a crossbow. They both can be incredibly accurate but when you move from an arrow to a bolt the difference in mass makes the impact much stronger (as Tywin Lannister found out that fateful night on the commode for you GOT fans out there). When the source tells the CDM to punch it, the CDM says “how high?”, even when going high means reaching low, hitting you deep in the gut (again, reference Tywin Lannister…). And talking about impact, if you want to see what a good DAC/amp really does for you then get a CDM and an iPhone camera adapter (Lightning to USB). Then listen to the same track via the iPhone’s (mine’s an iPhone 6) headphone jack and then through the CDM. Wow. Anyone who isn’t knocked over is either: 1) deaf, 2) not anyone who should be reading a review on Head-Fi, or 3) really, really loves Steve Jobs and thinks Apple products are bullet-proof in every way. The impact, the resolution, the pure musicality is night and day.
After listening to the CDM using the standard 3.5mm TRS cable I moved to a balanced cable (ALO Tinsel 2.5mm TRRS to silver barrel “custom IEM” 2-pin). This added even more to the soundstage and detail retrieval. In terms of the soundstage it takes what is impressive and gives it more depth, while the resolution also bumps up a notch, with more air between the instruments and micro-details. So for fun I switched from the K10’s to the LCD-3’s (the F model) and flipped the CDM’s switch to higher gain. OH MY EFFIN LORD. The CDM powered the LCD-3’s much better than I thought it would, bringing plenty of power to the party. It clearly needed the High gain setting, maxing out on Low gain, but then it only used half of the volume range to play the Audeze’s plenty loud. Seriously, if I was told I could only have one piece of gear to drive both my CIEM’s and full-sized cans I would take the CDM in a heartbeat and be perfectly happy, knowing that I wasn’t giving up much in performance to a much larger and more expensive desk-top system.
For more SQ information here are some of my notes for specific artists and titles:
  1. The Eagles, Hotel California: The bass line is much more “alive”.
  2. London Grammar, Strong: The squeak on guitar strings, the space of her voice, the impact of the keyboard bass line – completely more 3-dimensional.
  3. REM, Laughing: The bass line and kick-drum both have real texture and nuance, even though they are roughly in the same frequency range, a nice trick.
  4. The Chieftains/Diana Krall, Danny Boy: So amazingly emotional!
  5. Peter Gabriel, The Barry Williams Show: Incredible bass section, both the bass line and the kick drum and CDM is the best I’ve ever heard it sound on my K10’s – again real texture and impact without drowning out the high hat or Peter Gabriel’s fine vocals.
  6. Coldplay, Always in My Head: The texture and tone of the bass line is fantastic. This is a strong bass line no matter what you play it on, but on the CDM it’s like it adds another dimension, moving from 2D to 3D as you can now hear and almost feel the texture of the notes coming off the bass. Also the duration of the notes is like they’re hanging in midair.
Clearly lots of good stuff on a bunch of different types of music.
So some downsides to mention – hey, I roll transparently my friends! First the extra resolution comes with the typical price – you get to hear the stuff you weren’t necessarily supposed to. A number of times I’ve sworn that I hear a “hiss” from the amp, but each time I stop the music and fiddle with the CDM I realize it’s not the amp, it’s what has been recorded on the track. Bad recordings sound, well, not so hot. Second, and most importantly, the CDM is highly susceptible to outside interference. ALO wisely points out that you should keep your cell phone away from the CDM, and they’re right. Interference is such that you want to make sure your CDM is not near your phone or anything else giving off a lot of noise or is actively transmitting. I don’t have any issues with hiss when nothing is playing, but I can hear some interference quite often if I’m not careful with where I place the CDM. Seeing how hot it gets, you’re going to want to be careful where you put in any way! So keep your smartphones away, and also be careful with some computers how close you put it, as I found that to be an issue with my computer since it has a built-in broadband card as I got the same cell-signal interference. One the plus-side if you want to get all Jason Bourne you could potentially wave the CDM around and see if there are any listen devices hidden in your room. Third, while the CDM is technically and practically portable, it’s pretty big and not that convenient to hike around. On flights of ~2 hours or less I just use my trusty Rx stacked on my Fiio X3. For longer flights where I’m going to settle in for a bit I’ll pull out the CDM and the related cables and watch people get nervous as they wonder what they hell I’m powering up as it starts to glow. However, once I’m at the hotel (yes, I travel a lot) the CDM is my go-to source of audio bliss.
*** (Yep, observation time – talk about a total non-sequitur!). Okay, I’m now naming what I believe to be core element of head-fi, which came to me as I was reviewing the CDM and that I’ll very humbly call “Michael’s Law” (yes, that’s what the “m” stands for in mscott58 if you didn’t know). My observation is this – the better something sounds the less you pay attention to the equipment in the moment. This last part is important. When we get drawn into the music, at a basic and almost spiritual level (almost) everything else seems to go away – you are just one with the music. At some point thereafter, whether it be a few seconds or a whole night’s worth of reference tracks later, you snap out of it and say something like “holy crap, that (insert equipment name) sounds amazing!” (just like I did with the CDM on a few occasions). I think this is also a key element of audiophilia (is that even a word?), that to listen best we must listen with our hearts and souls. Forget about the numbers of drivers, the bit-rate, the composition of the cable, the age of the tube, whatever (and yes, even the price of the component) and just listen - let yourself get taken away. The further and deeper you go, the better. And I don’t give a rats-ass if that piece of equipment cost you $5 or $5,000 - enjoy the experience, wallow in it like you’re Wilbur after winning the county fair, lose some sleep, write silly reviews that use too many pop-culture references, call your friends over – whatever it is that makes you happy. And then be willing to accept that this experience that was so important to you will likely not be replicated for a good percentage of your friends/fellow HF enthusiasts. This happens so often that “YMMV” should be tattooed on the back of all of our hands so that we see it when we start flaming each other on the boards, using phrases like “it can’t” and “you don’t get it” and “zip-it Lachlan” (sorry, couldn’t resist). Back to my point, which is getting quite long I know, but the more you’re looking for a difference (like the damned and dreaded double-blind test), the more you want to find something and you risk focusing so hard on this that you lose the music, that you move away from the thing that we all should really (IMHO) be seeking – that true musical bliss. So the harder you have to try, the more you are focused on the equipment the less that piece of gear is really doing it for you.
Time for a very snobby analogy (but hey, we never judge each other here right? Ha!). Anyway I have been lucky enough to drive a fair number of very nice cars, and I had a similar “observation” driving something that costs so much it makes my head spin (and you think we have an expensive hobby?). So as a kid I always loved Lamborghinis. Heck, who grew up in the 80’s and didn’t have a picture of a Countach somewhere in their room? (I had both a picture and a model I had made and painted to look like the coolest cop car ever). So fast-forward a few decades and I got to drive a Lambo for the first time, and really drive it on a private 1.7 mile road course along with a Ferrari and a few other TOTL cars. Now I’ve always respected Ferrari’s, but the Lambo was my first real car-crush as a teenager. And guess what – I found myself wanting to like the Lamborghini (a Gallardo) so much, that this was what I was thinking about, not the driving experience. And like most ‘first-time’ things, it wasn’t all that enjoyable – likely for either of us. Juxtapose that with the Ferrari, where I wasn’t all giddy about the manufacturer (although they are “so choice” as Mr. Bueller would say) but I soon found myself completely lost in the driving experience. I became one with the road as that Italian beast slid around the track at speeds that I’m glad my wife didn’t see me post. I wasn’t thinking about the car or how much it cost or anything else really, I was lost in the moment, becoming one with the machine, experiencing and enjoying what it was built to do, and how I interfaced with it. This is how we should be with audio gear – lost in the music, letting the gear help us get there versus having the gear be the destination. For those who agree with “Michael’s Law” (okay, I admit the name is stupid, we can surely find something better and no, Warren or Wata, you don’t get to just put your own name it) let’s never forget to keep our focus on the music.
Okay, now back to the review – this is a review, right? Wait, what was the product again? Oh, yeah, the red-hot ALO CDM. I think it’s about time for a conclusion (as we rapidly head towards 4000 words and beyond). The CDM is an amazing amp/DAC on almost any scale, but is even more amazing when you consider that it is portable, it uses tubes and allows for easy rolling. Pricey? Yes. Worth it? Definitely. Ken and Vinnie, well done my friends, well done. 
@ mscott58, Honestly, I could not ear a difference... Those are very good tubes. I tend to lean toward the 6021 these days either the Mullards or the Sylvania brown label. I need 2 CDM to do this AB testing properly :), it is very difficult to do it with one only. I am using my Oppo HA1 as a reference so I can get the deltas between tubes with quick A to B connections, but that is not ideal. Also I have tried my last A/B testing with the HE1000 and this is a mistake as it is too forgiving. This need to be done with headphones which are less forgiving, So I came back to my LCDXC for these test. 
@mscott58 , Very many thanks for your amazing rewiev .
@kikouyou - I hear you. Hard to A/B when you have to go through all of that to change the tubes out. 
@Submariner2 - Glad you liked it! 
Next will come the CDM vs. Mojo input, with some teaming up of them as well! 


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