Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Propeller Head Plaza ]

---

[ Alert Moderator ]

---

Re: On a different note: Response to Morricab on Amplifiers

Posted by morricab (S) on February 14, 2007 at 03:28:39

In Reply to: Re: On a different note: Response to Morricab on Amplifiers posted by theaudiohobby on February 13, 2007 at 16:15:15:

"Class A circuit by definition cannot have crossover distortion "

Wrong again. Sure a single ended Class A amp cannot have crossover distortion...its single ended but a complementary design can still have some distortion at zero crossing if the transistors are not perfectly matched (and they are never perfectly matched). If they were perfect complements of each other and running true Class A then there would be no crossover distortion but we are talking about real amplifiers, right?

"Moving on, a Class AB circuits are symmetric not asymmetric, the article you cited simply notes that asymmetric signals are capable of exposing more distortion than a symmetric signal. Crossover distortion is easily suppressed by correctly biasing the circuit, with good circuit design, crossover distortion can be suppressed to vanishingly low levels, i.e. levels at which it is barely measureable."

Wrong again. Please look at page 3 of the article.

http://www.st-and.demon.co.uk/AudioMisc/distortion/page3.html

He states that asymmetric waveforms can heat transistors differently for each half of the wave cycle leading to dynamic differences in their bias. This leads to asymmetry in the output devices thus crossover distortion. I don't know what effects lead to asymmetry in SET amps or amps without feedback but it seems that music itself can lead to asymmetry in complementary Class AB amplifiers and that asymmetry is distortion. Bipolar transistors are especially temperature sensitive.

So the point is simple here, even with a PERFECTLY matched class AB design that measures Perfect with sine waves it will likely have distortions with real music due to asymmetry of the bias of the devices.

This post is made possible by the generous support of people like you and our sponsors:

Herbie's Audio Lab

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---