You should be use toroidal transformer, good rectifier diods (fast enough) and big high quality caps. All this things are necessary for good amplifier. Also I thing that 3A is to small for your need. It shoud be at least 5Amps transfomer. In most amplisfier designs there is no need for stabile supply voltage for output stage( it only must be filtered enough). For input stage you can easily make power suply with some LM317HV. Check this datasheet you will find out more.
Amp will be working without this, but not well.