EEL 4924 Electrical Engineering Design Project Design Report: J & J Mic Pre 2 February 2012 Team Members: Josh Levy & Jordan Leslie
Page 2/7 Project Abstract: Our project will be an all analog microphone preamp and an additional power amp stage to power speakers directly. The mic pre will amplify the voltage from a mic to a usable level, while the power amp will be used to drive enough current to a set of speakers if the user chose to use the pre amp with speakers. This project will be powered from a 120V AC wall outlet, so a clean DC power supply will be designed as well.
Page 3/7 Table of Contents: Introduction page 4 Features page 4 Technical Objectives and Considerations page 4 Standard Preamplifier Image page 5 Concept/Technology Selection page 5 Standard Differential Amplifier Schematic page 6 Block Diagram page 6 Cost Objective page 7 Materials and Resources page 7 Gantt Chart page 7
Page 4/7 Introduction: In the world of professional studio gear, mic pres rein king. It is extremely important to get the sound from the artist to some recording medium as clear and clean as possible to capture all the sonic characteristics as if the listener were there with the artist. Since the microphone signal is normally too weak to be transmitted to units such as mixing consoles and recording devices, the mic pre increases a their signals to a level required by these devices by providing stable gain while preventing induced noise that could potentially distort the signal. As this is the design objective of most mic pres, some users still claim each mic pre adds certain coloration to the sound or even has its own characteristics. So we wanted to make a design that is completely ours, by starting with designing our own discrete op-amp to be used in the mic pre. Features: The J&J Mic Pre will have multiple features. The list is as follows: Dual microphone input with phantom power option Ability to utilize dynamic and condenser microphone High fidelity gain Real-time headphone monitoring Technical Objectives and Considerations: The main objective of our project is to design a low-noise mic pre and a power amp. The first problem is impedance matching the source impedance from the mic with the input impedance of the mic pre, which is where the mic input transformers would come in The next problem is the actual low-noise pre amp circuit which will consist of a low-noise discrete parts Slew Rate Noise Bandwidth Common Mode Rejection Ratio (CMRR) We would like to be compete with the standard market op amp on entry-level preamplifier products
University of Florida Page 5/7 EEL 4924 Spring 2012 24-Jan-12 Figure 1: Standard layout of a mic preamp Concept/Technology Selection: The concepts we need to consider first are the basic op amp configurations and their specifications for each, such as gain, output impedance, and noise ratio. We will implement different topologies and compare them to one another. Using discrete parts, we need to ensure the differential pair of the op amp is closely matched to each other to ensure high fidelity gain.
Page 6/7 Figure 2: Differential Amplifier Block Diagram: Figure 3: Block Diagram of Final Product
Page 7/7 Cost Objectives: Parts: $300 Board Mills: $100 Casing: $250 We will attempt to stay within our budget of $1000. We will also include a detailed list of components as we decide on the necessary parts for our project Materials and Resources: Power supply transformer and mic input transformers, which will most likely be the most expensive parts in this project. Gantt Chart: (More detailed Gantt chart will be provided upon updated PDR)