For reference, I have posted the results of the ALO Audio CDM’s RMAA tests here.
I spent a paragraph or two describing why CDM isn’t a portable amp. What I didn’t say was that it is almost perfectly suited to earphone setups. Right now I’ve got it plugged into the super-sensitive Ultrasone IQ (reviewed here). When fed by an iPhone’s USB signal on low gain, I can rotate the volume pot by around 20º before volume gets too loud. When fed through the iPhone’s headphone output, I get about double that. Additionally, balance between left and right channels is very good, even at low volume levels.
In low gain, the CDM outputs minimal amounts of hiss: it is lower than both the AK100 and early iPod nanos. In high gain mode, it hisses slightly more than either unit. Meaning: custom earphone people, ortofon e-Q8 people, Ultrasone IQ people, you’re in luck. Who may not be in luck are Shure SE846 (reviewed here) users. As much as I love it, the SE846 is too sensitive. And the CDM is a powerful amp. If you’re keen on using it as a DAC with your iPhone (whose software is incapable of dropping the CDM’s volume), you’ll blast your ears. Of course, in OSX, Windows, Linux, Haiku OS, etc., pre-DAC volume levels can be adjusted from within playback software. In which case, you’re in luck.
Conversely, if you’ve got a high-impedance headphone, employing CDM’s DAC will net you more volume. CDM won’t bleed your DT880/600 anything like TELOS. At its highest volume setting, and when fed a USB signal, it spits about 20dB more volume than I can comfortably take. And CDM performs near flawlessly right up until a full twist of the volume pot, in either gain mode.
Its personality diverges somewhat based upon which input, digital or analogue, it is fed. The biggest difference is the DAC’s software low-pass filter, which gently rolls off high frequencies by about 3dB at 20K.
And low notes are more fibrous and contrasty when CDM is fed via USB. Despite its high-frequency roll off, with CDM’s DAC running the show, low-to-high contrast is the name of the game.
Fed analogue signals, CDM’s sound signature is shaded by super fine gradient fades within each frequency band, allowing you to hone in on the small things: the soft donk of the kick against the bass drum, the ringing forward edge after in the press of a piano key, the connective whispers between words as Mark Knopfler Communiqué’s with fans. Beyond the micro, each element pulls together in a perfect blend into which you can sink just as much ear into percussion as you can into vocals, into strings, into wood. The photographer in me wants to equate this with the classic 10,5cm f/2,5 LTM and SLR Nikkor tele portrait lens for 35mm cameras: sharp as a tack, but not so contrasty that it defaults greys to black. So flattering was that lens that it and its 85mm predecessor essentially put Nikon on the international map in a day when Leica was everything. And yes, I’m saying that CDM is audiophile equal.
Not that ALO are starving for attention or market. But CDM, more so even than Studio Six, is bound to redefine what people expect from the Oregonians. It is that good.
The contrast, great infra-frequency detail, and soft, deep gradients CDM serve make a superlative match to midrange-wide, contrasty headphones like the DT880, the IQ, and melt softer-sounding headphones like the Oppo PM-2 as sweet as peas.
But if you want that extra bite, that extra contrast between highs and lows, plug CDM into something USB. Bass gets bolder, highs and upper mids get shinier. Either way, CDM softens transients in typical valve amp fashion, but remains as stable as a good solid state amp.
At macro level, CDM nails everything.
And most-importantly, it is load-agnostic. Plug in your favourite earphones, or your favourite headphones and you’ll get the same base sound signature. No frequency drop outs, no sudden, violent peaks. You’ll get the sound ALO designed sans aberration. The only area CDM gives up under the heavy load of low impedance earphones is stereo separation. Still, under the load of the Earsonics SM2, it manages an impressive average of 66dB.
As with most amps, it completely ignores the load of the DT880, of the HD600, etc. And because it supplies nearly perfect signal even when dialing its volume pot fully up, if you really want to hurt your ears you can, and you’ll go deaf under quality signals. But no matter what you do, CDM won’t get your DT880/600 as loud as a powerful desktop amp.
That is, unless your DT880s are balanced, in which case, they’ll go another 10dB or 15dB above the volume to which CDM drives them in single-ended mode. Pair that with USB and BAM! You’ve got power.
Plugging into CDM’s balanced output lowers both THD and IMD distortion to levels nearer those of a solid-state amp. And, it eliminates stereo crosstalk by a further 7-10 decibels. Each of these is immediately audible. If you’re into the more intimate sound of valves, my suggestion is to work the single-ended line inputs and outputs. If you’re into bite and verve, try USB and balanced. You’ll also get a LOT more power that way.
I’ve got three favourite headphones to pair with CDM:
Campfire Audio Orion – this somewhat laid-back earphone has this strange thing for the CDM’s ultra-textured, smooth gradient bass and contrasty USB feed.
Ultrasone IQ – this earphone needs valves. CDM’s absolutely stable signal and smooth gradients turn this sometimes-gratingly contrasty earphone into sweetness and light.
Oppo PM-2 – not only is this my new favourite headphone, it melts when plugged into an analogue-fed CDM. Lovely in every way possible.
CDM is stable, powerful, wonderfully machined, beautifully branded, and a great match for everything from sensitive earphones to full-size headphones. Its brilliant DAC even nails native DSD decoding, adds spicy contrast, and a thoughtful low-pass filter. CDM even does balanced, from the DAC or the wire. It is expensive. It takes up the same footprint as an iPhone 6 Plus. It gets hot.
But if you’ve got an extra spot open in your mains, and you want a great amp or DAC that pays homage to the soft, warm valve sound, but under load remains as stable as a Vorzüge PURE II, CDM is your best option.
Again, this thing is destined to redefine what you, me, and the dudet down the audiophile street, know about ALO Audio. Awesome.