Hi Cliff,

The SMPS is particularly cool and quiet running, and its inevitable that a linear supply will make that worse. The supply itself is physically noisier, some of them unacceptably so, though the large Condor and Power-One supplies are very quiet.

They still disipate more heat than the SMPS though, so this is only going to make it more likely that the fan would come on. Whether that actually happens will depend on the ambient temperature and the degree of local ventilation. I wouldn't assume that the fan won't come on, and I wouldn't set the fan control to "Always Off". I'd leave it to the default "As Required".

I'm trying to minimise all these downsides by various means though. Choosing a large, over-rated supply will mean that the transformer is lightly loaded, and runs more quietly (and with less ripple!) Large supplies have larger heat-sinks, and will run cooler.

Using the CP498 means that the "hot end" sits above the fan and the air inlet, giving convection cooling the best chance. The CP498 also enables me to easily de-couple the transformer from the heat-sink. Part of the noise comes from the vibration from the transformer coupling directly to the heat-sink & chassis. Mounting the xformer in rubber bushes (but still with an earth strap) reduces noise very effectively.

This also enables the heat sink to be regidly mounted to the controller chassis, allowing the chassis to contribute to the heat-sinking. The LPS heat sink on my 861 is rubber-mounted to the chassis, which in hindsight is the worst case. The ideal configuration is a compliant-mounted xformer and a hard-mounted heat-sink, which is what I'm proposing here.

The short of it is that there are several things that can be done to manage heat and noise, but I'd assume that the fan will come on from time-to-time.

BR, Nick