Here's the SOLA site with all the details if interested: http://www.emersonindustrial.com/en-US/documentcenter/EGSElectricalGroup/products_documents/control_power_solutions/xformers/buck_boost_xformer/buckboost-xformers/buck_boost_transformer_catalog_pages.pdf No, these xfmrs do not hum loudly like the SOLA voltage regulators. Charlie