AES Store

Journal Forum

Audibility of a CD-Standard A/DA/A Loop Inserted into High-Resolution Audio Playback - September 2007
10 comments

Reflecting on Reflections - June 2014
1 comment

Quiet Thoughts on a Deafening Problem - May 2014
1 comment

Access Journal Forum

AES E-Library

Feedback, Sensitivity and Stability of Audio Power Amplifiers

Many audio power amplifiers consist in essence of a long-tailed-pair first stage, a lag-compensated common-emitter second stage with its emitter on a supply rail, a complementary-emitter-follower output stage, and overall negative feedback. This basic topology is analyzed for sensitivity to changes in various circuit elements, and hence for the effectiveness of feedback in reducing the distortion associated with nonlinearity in these elements. It is concluded that there are two quite distinct types of nonlinearity in the output stage-current nonlinearity and voltage nonlinearity-and that the effects of feedback on these are quite different. Distortion associated with a current nonlinearity (such as ß mismatch or saturation in the output transistors) can be reduced arbitrarily by increasing ß of the second-stage transistor (for example, by using a high-order Darlington) without any first-order penalty in either system stability or transient intermodulation distortion. In contrast, distortion associated with a voltage nonlinearity (such as the exponential V-1 characteristic of a transistor, or a deadband in the crossover region) is first-order independent of second-stage ß and can be reduced only by increasing the system closed-loop bandwidth. Increasing the closed-loop bandwidth tends to provoke high-frequency oscillation. It is shown that a small unbypassed emitter resistor in the second stage has a profound stabilizing effect, but pays no first-order penalty in sensitivity or distortion of either type.

Author:
Affiliation:
JAES Volume 30 Issue 5 pp. 282-294; May 1982
Publication Date:

Click to purchase paper or login as an AES member. If your company or school subscribes to the E-Library then switch to the institutional version. If you are not an AES member and would like to subscribe to the E-Library then Join the AES!

This paper costs $20 for non-members, $5 for AES members and is free for E-Library subscribers.

Learn more about the AES E-Library

E-Library Location:

Start a discussion about this paper!


 
Facebook   Twitter   LinkedIn   Google+   YouTube   RSS News Feeds  
AES - Audio Engineering Society