Temperature and implementation

Class D is “cool” in terms of how much power gets dissipated. If one were to heat-sink a class D amplifier like an equivalent class AB amp, they would remain utterly stone cold. The idea of course is to make the amplifiers more compact by reducing the heatsink. An idling UcD™ amplifier draws up to 2% of rated power. That’s 8W for a UcD400 amplifier. Whether that translates into a small or large temperature rise depends on the size of the heatsink. Please refer to the "Thermal design" application note for more information.
Yes! Never operate the amplifier without a heatsink or you will risk overheating it. Even the 90% efficient UcD700 running at full power dissipates as much as 70Watts. Simplest solution would be an all-aluminum case to which the amplifier is mounted. When using a steel case a regular aluminum heatsink should be used inside. Make sure there is always some airflow through the case by means of venting holes. Please refer to the "Thermal design" application note for more information.
Our modules are factory trimmed for best THD, not operating current. Operating current varies over a 20% range. The temperature difference is clearly noticeable but not a cause for worry.
We have an application note available for customers who wants to build high power touring amplifiers, please contact our sales department for personal guidance at sales@hypex.nl