Report Stereo Audio power amplifier 2 x 40W - 80W in Electronic Projects Design/Ideas Posted July 16, 2006 ok you are right but how much ampere should i have , a transformer of 2x38VDC @ how many amperes ??? A . what i think it would 500VA so if i multiply by power factor which i don't know , but assuming , it to be 0.5 , it is 300W that is 4A , so the transformer should be rated at 2x38VDC @ 4A , or else .. what do you suggest ???