The Sweet Spot by Nelson Pass

Every audiophile understands the term - that confluence of conditions that elicits the best performance, whether it’s a particular listening position or components that complement each other sonically.

Finding the Sweet Spot depends on selecting, adjusting and balancing these conditions for each part. Equally important is knowing the Sweet Spot when you hear it – it’s not always simply the lowest measured distortion. Nelson has written an article on the relevance of the Sweet Spot in amplifier design and some of the techniques that get it there...... download complete article

 

Audio, Distortion and Feedback by Nelson Pass

Audiophiles seem to revel in minor controversies – vinyl vs CD's, tubes versus solid state, capacitor, wires, magic dots... and negative feedback.

At one extreme, the position is that “feedback makes amplifiers perfect”. At the other extreme, “feedback is a menacing succubus that sucks the life out of the music, leaving a dried husk, devoid of soul”.

Feedback is very large subject, and I am going to limit myself to some simple tutorial comments and a discussion of phenomena associated with complexity in distortion created by nonlinear gain stages, negative feedback, and the audio signal...... download complete article

 

Leaving Class A by Nelson Pass

The meters on our amplifiers are different. They reflect the current consumption of the amplifier, and when the amplifier is operating, they don’t go down to zero like the meters on other amplifiers. 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 amplifiers 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 Class A has a high bias current. Class AB push-pull amplifiers are hybrids between Class B and Class A. Class AB run Class A at low power levels, and become Class B amplifiers at output currents determined by the bias.....download complete article