Does anyone know if the input to an old TRC931 is source selectable inside? I know some of the older boomboxes had different input transformer taps you could use - or even just a switch. If not - is it an easy changeover to put in an old US TRC931 input transformer (IF i can find one) - or do they make an aftermarket transformer of the right size and shape i could use INTERNALLY? i'm not really interested in an external series of plugs.