Measuring TIM

This paper by Leinonen, Otala and Curl investigates the measurement of TIM, a hot topic in the 1970’s and early ’80’s after its potential to cause sonic degradation by the incorrect application of feedback around high loop gain solid state amplifiers.

Now days (2017), there is a very complete and thoroughly in-depth understanding of TIM and related SID and how to ensure it can never take place. Modern VFA amplifiers overcome TIM by ensuring the front end gain stage gm is low (enough) and  there is sufficient current provided by the input stage of the  the amplifier  to quickly charge the integrating compensation network around the TIS. Further, new compensation design techniques such as TMC, OIC, TPC  (see Bob Cordell’s book ‘Designing Audio Power Amplifiers’ for more details) allow large amounts of feedback to be applied around amplifiers with improved sonic fidelity and none of the problems early solid state amplifiers were plagued with.

Measuring TIM.pdf

For a discussion around this topic and an overview of how the audio industry solved the TIM/SID problem,  take a look at ‘Solid State Feedback Amplifiers: A short History’