Further Development of a High Gain Microphone Preamplifier : API 500-Series Compatible Module
Petteri Taponen · Theseus (Ammattikorkeakoulujen) · 2017
The purpose of this thesis work was to improve an existing microphone preamplifier design for Sandhill Audio Oy in order to accomplish better distortion performance and better suitability for digital control of the unit. The environment the preamplifier will be used in, as well as its boundary conditions are introduced in the first section of this thesis work. Most recording chain components are briefly explained and signal level ranges are investigated. The main design focus was put on improving the analog circuit design, although, for the sake of clarity the basic structure of the digital control system is also briefly explained. The front end gain structure was designed to accommodate a digitally controlled relay switching, the equalizer was changed from active to passive and the drive capability of the output section was drastically improved. Also an improved level indicator circuit was introduced. To accomplish one of the most important targets, low distortion, characteristics of the input and output transformers were examined in depth. Also operational amplifier nonlinearities were measured and the circuit was fine-tuned for lowest possible distortion. The result of this thesis work is an optimized design of the analog circuit operating in an API 500-series environment. The circuit is a very high performance preamplifier which is ready to be applied in a production unit with very little or no changes.