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DSP Effects Guitar Amplifier

DSP Effects Guitar Amplifier. Rob Hermonat Greg Mucha Lucian Popa. Project Overview. Emulate sought-after tube/analog distortion found in various guitar amplifiers through the use of a DSP

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DSP Effects Guitar Amplifier

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  1. DSP Effects Guitar Amplifier Rob Hermonat Greg Mucha Lucian Popa

  2. Project Overview • Emulate sought-after tube/analog distortion found in various guitar amplifiers through the use of a DSP • Develop digital signal processing stage to emulate various brands/types of amplifiers (Fender, Marshall, Mesa Boogie & Roland) & create sound effects to enhance musical signal • Design and PCB layout of class D amplifier

  3. Project Block Diagram

  4. Digital Signal Processing • Converts analog signal into discrete sequence of numerical values • Use of computational algorithms for signal manipulation • Limitless possibilities for signal/sound effects • Relied heavily upon in music/movie industry

  5. DSP Based Effects • Equalization and Linear Effects (Reverberation and Delay) • Non-Linear: Tube Modeling

  6. Comparison Between Filters

  7. 5-Band Equalizer Design

  8. Why DSP? Analog is expensive and heavy

  9. Schetzen Formula

  10. Amplifier Considerations • Vacuum tubes (larger, high power consumption, shorter lifespan) • Class A (10-20% efficiency) • Class B (High efficiency/crossover distortion) • Class AB (35-55% efficiency, very common design) • Class D (Up to 90% efficiency/low distortion, new full-range audio designs)

  11. Class D Amplifiers • Full audible range amplifier (20-20kHz) • High efficiency • Low current (power) consumption • Low thermal by-product (small heatsinks) • Small footprint (compact designs)

  12. Class D Schematic

  13. Design Considerations • Quality of Sound • Cost • Availability of Parts • EMC Issues • Aesthetics • Portability • Feasibility

  14. DSP Features • 24-bit Symphony DSPB56371 Digital Signal Processor, 180 (MIPS) at 180 MHz core clock • Powered by USB bus voltage or external power adaptor (6-8 VAC or 8-10 VDC) • On-board USB interface that provides JTAG debug, I2C and SPI serial communication with the DSP • 3x AK4556 24-bit 192kHz stereo codecs • On-board microphone and pre-amplifier

  15. Specifications • Output Power 60 Watts RMS (8Ω Load) • 80-90% Efficiency at Full Power • THD (Total Harmonic Distortion) < .1 • DSP Sampling Rate 48 kHz • Maximize Execution Speed Through DSP Portion to Prevent Lag Times (Real-Time I/O)

  16. Class D PCB Layout • 2 Layer board • Flooded ground plane (top and bottom) • ExpressPCB Software • “Standard board” (No silkscreen or solder mask)

  17. Class D Amplification Stage • Gain of amplification stage • Buffering stage = 6 dB (at maximum volume) • Differential op-amp stage = 7 dB • Class D chip amplification = 23 dB • Total amplification: 23+6+7=36 dB ( about 63x) • Heat dissipation calculation • P = ( Tj – Ta ) / Rja. Where Rja = Rjc + Rch + Rha) • Tj=150 C; Ta = 50 C; Rjc= 2.52; Rch=1; Rha = 4.7 • Pmax = 12.14W

  18. Freescale Symphony Soundbite™

  19. Conclusions • Learning curve for using DSP much larger than expected • Mapping of A/D and D/A more important than resolution • Tube modeling and Class D combination result in improvements in size, weight, efficiency and reliability • Digital filters can be a cost-effective alternative to analog filters • Cascade 2nd order sections for more attenuation • Class D amp IC’s drastically reduce footprint although device size is still restricted by the size of the heat sink

  20. Questions/Comments?

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