作者:millwood时间:
supply rail voltage is usually determined by your transformer and is fixed.
what you can change is the idle current. so the right question should have been, given my transformer, what is the right idle current?
here is a rough calculation.
let's say that you have a 27vac transformer. the DC output is about 27vac*1.3=35v. assume that you use bjt output devices and the saturation voltage is 1v, the maximum voltage swing on the load is then 35/2-1=16.5v.
further, we are designing for a 6ohm load (fairly typical for an 8ohm nominal impedance speaker), the peak output current is 16.5v/6ohm=2.5amp.
that means the idle current is 2.5amp/1.3x=2amp, assuming a push-pull output stage with a 1.3x multiplier.
each device will dissipate about 2amp*17.5v=35w. That's about the limit for a to247/to3p device rated at 100w dissipation (at 25c).
the whole amp dissipates about 35wx2=70w, and you for all likelihood will need a 100w transformer (27vac*2.5amp).
the o