Review: Tube Rolling The ALO CDM

Tube Rolling the CDM – A guide to get started

Before you start rolling in different tubes, do check out Ken’s videos on how to handle the CDM/PCB and how to install the tubes.

The CDM’s reviews can be found HERE and HERE

Nathan, in his CDM review said: “CDM requires you to be familiar with bolts, screw drivers, ESD wrist bands, and elbow grease”. It’s no secret, I’d probably burn down the house if you gave me a soldering iron, but after having looked at the videos I immediately ordered one of those ESD wristbands (they’re really cheap) and started looking for tubes. My house hasn’t burned down (yet), the CDM still works and I’m still alive. So basically anyone can roll tubes in this unit. It takes about 5 minutes to open up the CDM, replace the tubes and close it back again. I have to say you kind of get the hang of it after trying a dozen different tubes. CDM still is cosmetically flawless, it’s built to roll tubes. One guy even dropped it but the CDM just kept working.

There are two kinds of miniature tubes available for the CDM: Single Triodes (green pcb) and Dual Triodes (black pcb). You have to pay attention when installing single triodes as the L/R markings are important as explained in the video. The dual triodes you can just plug in either slot on the board. The single triodes require less battery power and produce less heat, so in theory they are the ultimate tube but we all know our ears don’t always agree with the numbers.

All tubes below are compared to the stock Sylvania 6111WA. This test was conducted using two CDM units, one equipped with the stock tubes and the other with the after-market tubes. I used a Fiio HS2 signal switcher to select the CDM/tubes, a Resonessence DAC and the reference Hifiman HE-1000 headphone (CDM on high gain. Review of this beauty next week). ALO Audio sent me 10 different sets of tubes.

Something you do need to know: The differences perceived between these tubes are not night & day. Some differences are very subtle, some are easier audible but it’s never a completely different sound. So don’t expect a complete change in sound signature from rolling these tubes. The CDM is a hybrid tube amp and the effect the tubes have isn’t like with an OTL desktop amp in example. But there do are noticeable difference. It takes a good half hour for the tubes to sound their best. Let’s get started.

Sylvania 6111WA

Sylvania 6111WA

  • Showing good level of detail
  • Tighter and maybe drier/cleaner sound, which makes it excellent for fast paced music (like punk rock, grunge)
  • Bass doesn’t reach very low but has good punch
  • Good stock tube that doesn’t do anything wrong but it doesn’t excel either
  • Easier to listen to when music is really quick and busy (like punk rock)
  • 42°C is its temperature when warmed up


Mullard 6112


  • Smoother sounding.
  • Bass reaches deeper, is better layered. Maybe a bit looser and slightly less punchy but really good.
  • You get a very rich sound, especially in the mids. It sounds more spacious
  • Shows more extended treble with better layering
  • Wider soundstage and overall more airy sounding
  • 41°C


Sonotone 5719 (Single triode)


  • Treble is more layered, extended and slightly more focused
  • Like the Mullards they have a richer sound, especially in the mids. More spacious delivery
  • Bass reaches deeper, is better layered but looser. A slight less punchy feeling because of the more spacious sound but it body wise is closer to the stock tubes than the Mullard 6112
  • More airy sound, closer to the Mullards
  • Wider sound stage/more space between the instruments
  • Runs a lot colder to the touch (about 38°C but feels like a lot less)

It continues on Page 2, after the click HERE or below

4.6/5 - (16 votes)

Lieven is living in Europe and he's the leader of the gang. He's running Headfonia as a side project next to his full time day job in Digital Marketing & Consultancy. He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years.


  • Reply October 3, 2015


    Wow no comments yet? Well I liked this article – the CDM sounds like a winner of a niche device. I’m curious how it would work with my Ortho-type headphones.

    • Reply October 3, 2015


      Thank you, it took a lot of work. ALO was supposed to link to here from their site but they still haven’t.

      I really enjoy the HE1000 with the CDM, I haven’t really tried my LCD2 and LCDXC with it. And both my EL-8s are boxedup (not that exciting)

      • Reply October 3, 2015


        Have you listed to the MD Alpha Prime at all? – Do you think that would be a good match?

  • Reply October 17, 2015


    How does it pair with with the HD650?

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