DC offset for audio circuits

[walters]

What is DC offset?
Why is DC offset Bad?
What is Good DC offset?
What is Bad DC offset?
AC riding on DC offset or DC?
DC offset applies to both upswing (positive) and downswing (negative) waveforms
what does this mean?

[audioguru]

Hi Walter,
You are probably talking about the DC offset voltage at the output of an audio power amplifier that is direct-coupled to a speaker without a coupling capacitor.

The offset voltage is the DC voltage measured at the amp's output that is applied to the speaker all the time. It is never good:
1) It causes the amp and speaker to heat-up.
2) It causes the cone of a coil and magnet speaker to be moved away from its center position all the time, causing distortion and reduced power handling ability for both the amp and the speaker.
3) It is an error voltage that nearly all electronic circuits have. Very good amps have a trimpot that can be adjusted to null the offset voltage to zero. ;D

[Guest Alun]

Some of the more expensive op-amp ICs are laser trimmed to offset null.

[audioguru]

Yes Alun.
Good point! ;D ;D