Vinnie Rossi: "When Ken asked me to help him design an ALO Audio flagship portable DAC/amp, he really wanted one that didn't sound like a typical portable headphone amp but instead more akin to his Studio Six desktop amp. The only way to get the big open and rich sound of that was to use tubes as well. After a few prototypes which each saw lots of adjustments, part swaps and finally a version where we tried going dual-mono for the voltage gain stage (using one 6111 per channel) and solid-state output section (current gain), we were able to achieve a sound signature that did indeed have much of the Studio Six DNA. He also wanted a healthy dose of power which means twice the signal swing over the 2.5mm TRRS balanced output. To chase lowest possible noise and microphonics, I decided against step-up transformers or DC-DC converters for the tube stage. We instead feed the clean power from the battery pack directly to the tubes' B+ (anode) and bias the circuit for high bandwidth, a linear response that extends past 50kHz and to deliver remarkably low noise floor and microphonics. 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 a higher-quality conductive plastic potentiometer instead of the more common carbon tracker.

"Ken's demand for top-quality battery support had us go with the Panasonic NCR18650 cells, the same as used in the Tesla Model S electric car. Ours connect in series for a 11.1V nominal pack. These are widely accepted as the finest 18650-size Li-ion cells made. The pigtail of the battery pack uses a keyed 2-pin header to be easy to remove/replace when the time comes. The pack is rated at 3400mAh, 1'000 cycles and features built-in protection against over-current (e.g. short circuit conditions). For the PCM/DSD USB converter, we went with a Cmedia USB receiver chip, Wolfson's top-of-the-line WM8741, a separate ultra-low jitter clock generator chip and all linear voltage regulation. And Ken wanted a dedicated 2Vrms line-out jack so one can use the deck as just a DAC. Linear regulation throughout plus class A tubes in a portable size of course make for a hand warmer but that's by design."


Back on hand warmer and also size, the CDM isn't ideal as a pocket-carried portable where its vents wouldn't breathe properly. I think of it as really a stationary device to be used at home or away from home like in an office, hotel room, beach cottage and such. Placing it upright as you would in a pocket to have volume control and outputs on top has it sit on its source selector toggle. Flipping it sideways closes off one bank of perf holes. The proper orientation is on its belly. As somewhat of a flounder then, it'll be too big for most walkabouts. End of small print.


If the Vinnie Rossi connection has you expect sonics in line with his prior Red Wine Audio or current LIO aesthetic; and/or if you remember how he used to represent WLM speakers and routinely shows with Harbeth to draw certain conclusions from that - you'd be right on both counts. I call that comfort food sound: rich in calories, substance and served up large. It seems to be a combination of tube/transistor circuits on batteries and Vinnie's preferred voicing from circuit/parts tweaks.


With experience gained over many years and perhaps personal tastes refined, the 'Vinnie sound' now is about comfort food served à la fine dining. Which is to say, it's gained in presentational refinement but remains about big robust nourishing portions. From yours truly to John Darko to Herb Reichert, that sound has gotten high fives, awards and major kudos. Ergo it's not the lean speed-freak aesthetic with its forward treble, razor separation and pale colours. To get more specific means wearing a few cans which are known to lean that way—Sennheiser HD800 and beyerdynamic T5p come to mind—and quantify how much weight and colour gains they make from being CDM'd. Might that really stand for Colour, Dynamics and Mass?