If used at all, most digital transformers used in the outputs of CD transports or the input of D/A converters are cheap jobs with ferrite cores, in order to improve on this we have commissioned a toroidal core made from very thin laminate spun 80% nickel strip, housed in a small plastic “doughnut." Buy one, compare the quality and be prepared to be shocked, there are good reasons why our Level One and higher Level 1xoversampling™ D/A converters have the reputation they have and the digital interface transformers have a great deal to do with this.