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Audio Amplifier with Equalizer

Audio Amplifier with Equalizer. Project #33 Bryan McDevitt Jason Ohnemus Peter Keenan TA – Julio Urbina Thursday April 27, 2000. Audio Amplifier with Equalizer. Introduction Our purpose was to design an audio amplifier with equalizer

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Audio Amplifier with Equalizer

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  1. Audio Amplifier with Equalizer Project #33 Bryan McDevitt Jason Ohnemus Peter Keenan TA – Julio Urbina Thursday April 27, 2000

  2. Audio Amplifier with Equalizer • Introduction • Our purpose was to design an audio amplifier with equalizer • Our goals were to have around 20W output power while trying to minimize noise • To gain experience in design and construction of general electrical circuitry

  3. Audio Amplifier with Equalizer • Three different subprojects • Graphic Equalizer utilizing frequency filters • Amplifier built and designed at the transistor level • Power supply with the attempt to minimize noise from ac outlet

  4. Audio Amplifier with Equalizer

  5. Graphic Equalizer • Design Considerations • Analog or Digital • filter type • Butterworth or Chebyshev • Filter order • frequency ranges of each band

  6. Graphic Equalizer • Assemble 5 filters over the various bands • Input the signal into each filter • Use trimpots to attenuate signal on desired band • Sum the signals together before going into the amplifier

  7. Graphic Equalizer

  8. Graphic Equalizer • Low Pass Filter topology • Band Pass Filter topology

  9. Graphic Equalizer • Standard Equations used (from ECE353 Supplementary Notes - Spring 2000 by Professor Steve Franke)

  10. Graphic Equalizer

  11. Graphic Equalizer

  12. Graphic Equalizer • To test the analog design, used an oscilloscope • compared the input amplitude from a function generator to the output of each band • analog filters did not seem to achieve both passband gain levels and stopband attenuation levels desired • decided to try digital filters using a DSP

  13. Graphic Equalizer • Used FIR filters for each band • Obtained coefficients using the Matlab command remez to get Parks-McClellan filters • Tested using oscilloscope and observed desirable attenuation in stopbands and acceptable gain in passbands

  14. Graphic Equalizer • Input Wave to DSP (50mV wave at 2kHz)

  15. Graphic Equalizer • Output Wave from DSP (50mV at 2kHz)

  16. Analog Summer

  17. Audio Amplifier Design Considerations • Output Power • Efficiency • Noise

  18. Audio Amplifier Amplifier • Advantages of single-ended as opposed to differential amplifier • Single ended can be sent straight to output • Differential allows for more common power supply • Slightly more power with differential • Don’t have worry as much about noise with fewer stages

  19. Audio Amplifier • Enough gain so that 20W output can be achieved • Really didn’t need more than one stage due to size of input signal

  20. Audio Amplifier • Output Stage • Class A, B, AB • Class A – least efficient, least noise • Class B – most efficient, most noise • Class AB – average efficiency, average noise • Must be efficient enough to deliver 20W of power to speakers

  21. Audio Amplifier • Problem 1 - Using single ended diff amp caused half of the output waveform to be clipped. • Solution - Adjusted power supply so that waveform is shifted above where it was clipped

  22. Audio Amplifier • Problem 2 - Amplitude of original signal was too small so a lot of noise was being introduced • Solution - Doubled amplitude of input signal and reduced overall gain of the circuit

  23. Audio Amplifier

  24. Audio Amplifier

  25. Audio Amplifier

  26. Audio Amplifier

  27. Power Supplies • Design Overview Transformer Rectifier Filter Regulator AC Line from wall Load

  28. Power Supplies • Design Overview • Transformer used to stepdown 120V, 60Hz AC to a lower voltage • Rectifier used to eliminate negative portion of the sinusoidal AC • Filter used to Keep voltage at desired levels • Regulator used to designate actual voltage level

  29. Power Supplies • Transformer Options • Two types of transformers are usually used in power supplies • single-ended secondary • center-tapped secondary • both step 120V down to 25.2 • Using the center-tapped secondary transformer because of availability

  30. Power Supplies • Rectifier Options • Two basic types of rectifiers are usually used • half-wave rectifier • full-wave rectifier

  31. Power Supplies • Rectifier Options • Half-Wave Rectifier • Circuit Setup

  32. Power Supplies • Rectifier Options • Half-Wave Rectifier • Voltage/Time Plot

  33. Power Supplies • Rectifier Options • Full-Wave Rectifier • Circuit Setup

  34. Power Supplies • Rectifier Options • Full-Wave Rectifier • Voltage/Time Plot

  35. Power Supplies • Obviously Full-Wave rectification is a better choice • less time between peaks • means less time for capacitor to discharge • adds up to less of a ripple voltage • closer to DC • less noise

  36. Power Supplies • Rectifier Options • Final decision on Rectifier • Full-Wave Bridge Rectifier

  37. Power Supplies • Rectifier Options • Full-Wave Bridge Rectifier • provides electrical isolation between AC powerline and the rectifier output • can be used with either center-tapped or single-ended secondary winding transformers • when used with center-tapped can produce power supply with voltage twice that of each transformer end

  38. Power Supplies • Over all Design Options • Have decided on type of rectifier • Transformer type is set because of availability • center-tapped • Next step is to build the regulator • this means deciding on a needed DC voltage and a corresponding zener diode

  39. Power Supply • Regulator • regulator sets output voltage • consists of two components • zener diode (to set voltage out) • resistor (to limit current through the zener) From filter and rectifier

  40. Power Supplies • Graph with regulator in place

  41. Power Supplies • Overall design • We now have all the components except for the filter • As can be seen on the last slide we the voltage set, but there still is approx. a 6.5 Volt ripple • Designing the filter correctly will ensure a small ripple voltage

  42. Power Supplies • Filter Design • Filter is made up of one capacitor • Decide what is an acceptable ripple voltage • from that get capacitor value needed • we used a ripple voltage of 0.5% of desired voltage • Vripp (6.2V supply) = 31 mV • Vripp (25 V supply) = 125 mV

  43. Power Supplies • PSpice schematic with all modules in place

  44. Power Supplies • PSpice simulation

  45. Power Supplies • PSpice ripple voltage

  46. Power Supplies • Now let’s look at some actual data taken with an oscilloscope and HP-Vee. • You should notice that the Vpp is higher than PSpice ripple voltage • noise • non-ideal parts

  47. Noise for 6 Volt Supply

  48. Noise for 25V supply

  49. Second breakdown of Noise on25V supply

  50. Power Supplies • Ripple voltages are higher than in simulations, but still within the 0.5% of desired output voltage • Shorter lead lengths and sheilding for the circuit would help reduce the noise

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