Bias adjustment on solid state amplifiers

Thanks @erik_squires ,

Based on your answer, why would anyone try to change bias on a SS amp? 

For the original question generally bias is set at the factory during the initial check and then again after a burn in period. Transistors and FETs don’t age the same as tubes and so while it may drift it normally wouldn’t be too much. It will drift more with temperature and line voltage than with age. Doesn’t mean it can’t be done or checked with a service manual and volt meter if one wanted to.

My experience has been that bias and DC offset are two separate adjustments. Bias sets the standing current through the output devices and somewhat the transition into class B. DC offset zeros out any DC potential between the two output terminals.

Ideally, SS amp bias would be set according to the average voltage coming in on your mains. 

The main reason to increase the bias of a SS amp is to reduce crossover (i.e. notch) distortion, but it is not really something a consumer should do, and the benefits are rarely worth the risk to the transistors and power supply.

Where exactly to set the bias point for a given transistor is a matter of some art. Enough to eliminate gross distortion but not enough to warm the room.

Best,

E