Quote Originally Posted by foto-r3
This has to do with an OMEGA D5 Dichroic enlarger we recently bought here in Spain. To the best of my knowledge, these enlargers all came with the US voltage and were rigged-converted to 220V. Mine has two big transformers. The problem is: the enlarger works correctly but makes a annoying humming noise from the head --different from the otherwise quiet humming noise of the fan itself. When we hooked it up to a third-party solid-state voltage stabiliser, the fuse pops on the stabiliser every so often. I suspect that these enlargers do not normally make this annoying humming noise. Can anyone verify this, and, has anyone had a similar experience with voltage conversions and-or voltage problems that could shed some light on this...thanks.
I'm going to assume that the humming is still there even when you use the voltage stabiliser, if so then read-on. Also I'm going to assume that voltage stabiliser outputting 220VAC (rather than 110VAC).

The most likely cause of the hum would be the step-down transformer (220V-110V). If an under rated (power-wise) or poorly designed step down transformer is used you will over-load it causing hum. If there is a rating on this txformer then see how it's power rating compares to the power needs of the enlarger.

A humming transformer is operating inefficiently and will draw more power than it should. So if the fuse on the voltage stabiliser is chosen exactly for the enlarger (i.e. the ratings were chosen to match) then the additional (unnaccounted) power drain in the humming transformer core will blow the fuse (albeit intermittently if it is just over the limit since fuses are not binary in nature, they obey a time*current curve.)

So if that is the case, I'd get the step-down transformer replaced with one that can handle the power drain of the enlarger. If the step-down transformer is sufficiently rated then get another one anyway because it is probably a bad design ! Toroidal transformers are quieter conventional shaped (cubical ?) txformers and are used in audio amplifiers for this reason.