Hey All,
Some customers have noted the heat generated from the CDM.
The purpose of this post is to demonstrate the typical running temperatures of the CDM and further point out that the CDM, being a tube-based amplifier, does generate heat that is not typical with most solid-state portable amps.
BACKGROUND INFO
The CDM uses two 6111 subminiature vacuum tubes that will each generate approx. 2W of heat when running normally. These tubes are the main source of heat you feel from the CDM’s enclosure. In addition to this, some IC’s on the CDM’s circuit board (PCB) will also generate heat. The design of the CDM uses the enclosure as a heat sink that transfers this heat safely away from the PCB and dissipates this heat into the enclosure, where it then radiates to the outside air. It is
normal for the enclosure to operate in the 90 - 130 F (32 – 55 C) range. All of the CDM’s components are rated for operating beyond these temperatures.
When using its internal dac, the CDM will generate the most amount of heat - as we use linear voltage regulators to feed the DAC stages. Linear regulators are less efficient than switching regulators (DC-DC converters), but offer lower noise and better performance for high end audio applications such as the CDM.
We recommend that you:
- Do not obstruct / cover and vent holes of the enclosure, especially when using the internal CDM dac.
- Take care when touching the CDM to note that it does get hot to the touch, especially when in DAC mode
- Are mindful that the CDM is a tubed-based portable amplifier/dac, and it is
normal for tubes to generate heat, as they contain “tube heaters” (filaments) that are required to heat the vacuum inside to tube to function. This, along with the use of linear voltage regulators (above) where chosen for what we believe is the best sound quality in the smallest sized enclosure. Doing so requires the enclosure to get warmer than most portable and transportable amplifiers – especially those that do not use tubes.
TESTING
The typical temperatures we have documented are summarized in the following tests.
Testing procedures were as follows:
- Running the CDM in analog mode (dac not connected) - balanced line input to the CDM while driving both SE and balanced headphones simultaneously AND also charging the battery.
- Running the CDM in DAC mode - balanced line input to the CDM while driving both SE and balanced headphones simultaneously AND also charging the battery.
- Measurements were taken after the amp has reached its peak operating temperature, in this case after 1 hour of play.
- Temperatures were recorded via an IR thermometer at various locations on the exterior of the CDM (please refer to the following diagrams).
- Ambient temperature at the time of testing was 76F (24C). The stock tube used was the Phillips 6111 (note - temperatures will be lower if a single triode tube with 150mA filament current draw is used such as the 5719 or 5718) instead of the 6111 family with 300mA filament current draw).
The highest recorded temperatures in our tests was 123.9F (51C), however depending on the angle of the IR thermometer and the locations of the test, the temperatures can be marginally lower or higher.
Additionally the testing was done using a black CDM and the temperatures recorded were consistent with that of a silver unit.
As a reference, the recommended temperature of coffee that is safely drinkable sis 137F (58C) as reference is here:
http://www.ncbi.nlm.nih.gov/pubmed/18226454
Also interesting to note that, 1) Most people prefer to drink it in the 155F – 175F range, and 2) McDonalds was sued for
serving coffee in the 195 – 205F range and it causing burns when it spilled on a customer.
Thank you
Ken