Join Date: Jul 2004
Location: Scottish Borders
35Vac gives ~ 50Vdc, 35+35Vac gives ~ +-50Vdc.
Check through a few posts. You will find many estimating methods and a few that get much closer to reality. All involve the use of SQRT(2).
You need to know the rated input voltage as well as the rated output voltage of your proposed transformer. You also need the VA or current rating and the regulation figure of the transformer.
Finally you need the "normal" voltage available at your home. This "normal" varies from minute to minute and hour to hour, but should always be between the tolerance limits specified by your electricity supplier. Except when there is a mains failure where zero volts becomes available or "brown outs" when the available voltage falls below the lower tolerance limit.
As listeners we would not design for continued maximum sound quality during "brown outs". But we would design for "no damage" in event of mains failure and repeated attempts at restarts.