On Thu, Mar 02, 2006 at 03:04:29PM +0900, res0u2uc@xxxxxxxxxxx wrote: > Hmm. Well, my knowledge here isn't great, but I think having > a capacitor at the output of a Class A amplifier would > prevent it from operating with a DC offset. No. The essential point of (balanced) Class A is that both halves of the output stage (the one giving the + and the one giving the - voltage) are both active all the time and never 'cut off'. This doesn't imply there is any DC in the output signal, since this is usuaully the difference between the two halves, and so the DC cancels out. Anyway the DC component required for Class A would burn your speakers in a fraction of a second. > You're right about most gear using capacitors. Most > transistor amps are Class B or AB which output AC. Older > tube amps, however are usually Class A to reduce the number > of tubes, and like my dad's old Heathkit, have a big > transformer on the output. Transformers in tube amps are mainly there to do impedance matching, not to block the DC. There won't be any DC going into the transformers primary in a decently designed amp anyway - it would saturate the transformer and make it appear as a near short circuit to AC. -- FA
