Leaving Class A — Nelson Pass / 2008

The meters on our amplifi ers are different. They refl ect the current consumption of the amplifi er, and when the amplifi er is operating, they don’t go down to zero like the meters on other amplifi ers. This is because the electrical current consumption of our circuits has a fairly high value at all times, a property called the bias. The bias current runs through the amplifi ers at a minimum value, determining the class of operation – Class B, Class AB, or Class A. Class B has no bias current, Class AB has a moderate bias current, and… More...

Arch Nemesis — Nelson Pass / 2010

A poster of Einstein once said, “Things should be made a simple as possible, but no simpler”. This can apply to audio amplifiers, but if they are evaluated subjectively, the simplicity thing can get a little of of hand. Of itself, minimalism exerts a strong aesthetic attraction, and there is a reasonable belief that fewer components in the signal path allows more information to get through with less coloration. If like me you are interested in understanding of how we hear distortions with our brains (instead of our meters), you might appreciate that simple circuits help isolate these phenomena. I… More...