BASS GUITAR PREAMP DESIGN Dave Sampson I’d like to dedicate this work to my long term partner Louise. Without her love, patience and encouragement this work would not have been possible. Audiodomain.blogspot.co.uk 1 @homewith_dave [email protected] TABLE OF CONTENTS Chapter 1 ........................................................................................................................ 7 1.1 History .............................................................................................................................. 7 1.2 Aims & Objectives ............................................................................................................. 7 1.3 Summary of Report Structure ........................................................................................... 7 Chapter 2 ........................................................................................................................ 8 2.1 Existing Solutions .............................................................................................................. 8 2.2 Input stage ........................................................................................................................ 8 2.2.1 Input Signal ................................................................................................................ 8 2.2.2 Attenuation ................................................................................................................ 9 2.2.3 Impedance Bridging ................................................................................................... 9 2.3 Operational Amplifiers ...................................................................................................... 9 2.3.1 Specifications ........................................................................................................... 10 2.3.2 Op Amp Rules .......................................................................................................... 11 2.3.3 Amplification............................................................................................................ 11 2.3.4 Buffer Amplifier ....................................................................................................... 12 2.4 Filtering ........................................................................................................................... 13 2.4.1 Reactance ................................................................................................................ 13 2.4.2 Passive Filters .......................................................................................................... 13 2.4.3 Active Filters ............................................................................................................ 14 2.4.4 Multiple-Feedback Bandpass Filter Topology .......................................................... 15 2.4.5 Boost/Cut Topology ................................................................................................. 16 2.4.6 Filter implementation .............................................................................................. 17 2.5 Power ............................................................................................................................. 17 2.5.1 Power Supply ........................................................................................................... 17 Audiodomain.blogspot.co.uk 2 @homewith_dave [email protected] 2.5.2 DC Regulation .......................................................................................................... 18 2.5.3 Split Power Rail ........................................................................................................ 18 2.5.4 Decoupling ............................................................................................................... 18 2.6 Output ............................................................................................................................ 19 2.6.1 Operational Amplifier Based .................................................................................... 19 2.6.2 Ground Lift ............................................................................................................... 19 2.6.3 Output Impedance ................................................................................................... 19 2.7 Design Considerations ..................................................................................................... 19 Chapter 3 ...................................................................................................................... 20 3.1 Specification ................................................................................................................... 20 3.2 Schematic ....................................................................................................................... 20 3.3 Bill of Materials ............................................................................................................... 20 Chapter 4 ...................................................................................................................... 22 4.1 Modular Design ............................................................................................................... 22 4.2 Enclosure ........................................................................................................................ 22 4.3 Issues During Construction.............................................................................................. 22 4.4 Final Schematic ............................................................................................................... 24 Chapter 5 ...................................................................................................................... 25 5.1 Test Notes ....................................................................................................................... 25 5.2 Frequency Response ....................................................................................................... 26 5.3 Filter Performance .......................................................................................................... 28 5.3.1 Bandpass Frequency Response ................................................................................ 28 5.3.2 Summed Filter Response ......................................................................................... 29 5.3.3 Interaction ............................................................................................................... 33 5.4 Total Harmonic Distortion + Noise .................................................................................. 37 5.5 Signal to Noise Ratio ....................................................................................................... 38 5.6 Impedance ...................................................................................................................... 38 Audiodomain.blogspot.co.uk 3 @homewith_dave [email protected] 5.7 Current Draw .................................................................................................................. 39 5.8 Output Level ................................................................................................................... 39 5.8.1 Line Level ................................................................................................................. 39 5.8.2 Instrument Level ...................................................................................................... 39 Chapter 6 ...................................................................................................................... 40 6.1 Further Work .................................................................................................................. 40 6.2 Conclusions ..................................................................................................................... 41 References .................................................................................................................... 42 Appendices ................................................................................................................... 45 1: Electronic Circuit Equations .............................................................................................. 45 1.1: Ohms Law .................................................................................................................. 45 1.2: Kirchoff’s Current Law ............................................................................................... 45 1.3: Kirchoff’s Voltage Law ............................................................................................... 45 1.4: Thérevin’s equivalent circuit ...................................................................................... 45 1.5: Series Resistance: ...................................................................................................... 46 1.6: Parallel Resistance: .................................................................................................... 46 2: Commercial Preamp Specifications ................................................................................... 46 2.1: Tech 21, Sansamp Bass Driver ................................................................................... 46 2.2: East, STMP - 01 .......................................................................................................... 46 2.3: EBS,