Mark Harder
New Member
I'm a newbie here, so I'm puzzled by contradictory advice as to the secondary voltage required of a power transformer when building an audio power supply. I'm building a +/- 40V DC supply and the BOM for one design specifies a "42 - 45 V, 2A CT" transformer. Now, I'm pretty sure that, for example, a 22-0-22V transformer won't cut it since 22*1.414 is only ~30V AC, pp. So, I'm assuming that the authors meant a 44-0-44V transformer in this case. However, another plan recommends that I pick a transformer with a secondary voltage giving 1.414*V AC= ~5 - 10 V AC in excess of the required DC voltage. In this case, I would choose a transformer with a 32V to 35 V AC dual secondary to make a +/- 40 V DC power supply (45/1.414 = 32V & 50/1.414 = 35V). What is the true rule (of thumb or whatever) for picking transformer secondary voltages?