Design Review Presentation

1. Design Review Presentation Senior Design May06-01: Headphone Amplifier, Equalizer, and Sound Stage

2. SD May 0601: Headphone Amplifier • Features • 1/8” input • 1/8” and 1/4” outputs • Amplifier section • Five-band equalizer with slider potentiometer controls • Sound stage acoustic simulator with variable time delayed channel cross-feed • Internal power supply and removable battery pack

3. Functional Requirements • Inputs and Outputs • One 1/8” input and both 1/8” and 1/4” outputs • Amplification • Sufficient power to drive headphones ranging from 32 Ohms to greater than 600 Ohms and line level devices with negligible distortion. • Balance control to manipulate the volume ratio between channels

4. Functional Requirements Cont'd • Equalizer • Three-band logarithmicly spaced frequency bands • Stereo equalization, each band controlled from a singled ganged potentiometer • Sound Stage • Channel cross-fed and time delayed signal • Attenuation on the cross-fed signal. • Variable time delay between cross-fed signal and main signal to simulate

5. Functional Requirements Cont'd • Casing • 8”x8”x2” case size limitation • Durable case material, must survive a drop without internal damage and minimal cosmetic damage • Controls • Volume and balance potentiometers • Equalizer consists of slider style potentiometers • Sound stage controlled by an X-position switch • Power switch and indicator LED

6. Intended Uses • For the amplification and enhancement of personal audio device signals • Headphones of both the high (600+ Ohms) and low (32 Ohms) impedance variety • Line level devices • Powered desktop speakers • Car radio cassette deck adapter • FM transmitter

7. Project Schedule

8. Circuits • Amplifier • Limiter • Equalizer • Baxandall • Resonant Frequency • Sound Stage • Ohman Cross-feed • Linkwitz-Equivalent Filter with cross-feed • Douglas S. Bungart Patent # 5,751,817

9. STEREO OUTPUT SOUND STAGE LEFT LIMITER STEREO I NPUT LEFT PREAMP LEFT EQ BALANCE RIGHT PREAMP RIGHT EQ RIGHT LIMITER POWER SUPPLY The green lines represent components with ganged controls. The red lines represent power supply lines Circuits: Block Diagram

10. Amplifier • Consists of a single op-amp (per channel) • Inverting configuration • Negative feedback • Ganged potentiometer in the feedback loop for variable gain and signal attenuation • Gain requirements have not yet been solidified, as this is a simple change to make to the circuit and does not affect any other sections • Low-pass input filter • Corner frequency at 25kHz • Filters out high frequency noise before amplification

11. Amplifier

12. Amplifier: Testing • Fully functioning • Available gain dependent on power supply • If the output voltage exceeds the voltage being supplied to the op-amps, the signal is clipped • Gain range not yet set in stone • Dependent on how much gain needed to compensate for the drop through the rest of the circuit • Easy to set and modify the gain range

13. Limiter • Hard Limiter • Diodes configured to clip the signal once output exceeds a set level • Sound very bad, but does an excellent job of limiting the output • Soft Limiter • Paired LED and photoresistor • LED emits light once a certain output threshold has been exceeded; photoresistor resistance value increases and attenuates the signal • No loss in sound quality

14. Baxandall EQ • Five-band active equalizer • Single op amp per channel • Frequencies centered at (Hz): • 100 • 300 • 1k • 8k • 17k

15. Baxandall EQ Band frequencies were found by the following formulas: f_bass = 100 Hz = f_lmid = 300 Hz = f_mid = 1kHz = f_hmid = 8kHz = f_treble = 17kHz = http://headwize.com/projects/equal_prj.htm

16. Baxandall EQ: Testing • 5-band still undergoing testing • Measure boost and cut • 3-band tested and works • Cut band nearly to zero when tested

17. Resonant Frequency EQ • Five-band redesign from three-band circuit • Active • One op-amp per band • 10db boost / cut

18. Resonant Frequency EQ (part 1) http://headwize.com/projects/equal_prj.htm

19. Resonant Frequency EQ (part 2) http://headwize.com/projects/equal_prj.htm

20. Resonant Frequency EQ: Testing • Still troubleshooting • Redesign to use 10kW slider potentiometer • Redesign to increase gain to 25dB of boost and cut • Redesign bass and treble to shelf, rather than resonant filters

21. Brungart Sound Stage • Pinna filter to compensate for the transfer function of the human head and outer ear • Variable time-delayed cross-feed between channels • Time delay achieved by cascading active filter stages that each add approximately 150ms of propagation delay

22. Brungart Sound Stage Block Diagram http://www.headwize.com/tech/sshd_tech.htm

23. Brungart Sound Stage Aural Specifications http://www.headwize.com/tech/sshd_tech.htm

24. Brungart Sound Stage Time Delay http://www.headwize.com/tech/sshd_tech.htm

25. Brungart Sound Stage Pinna Filter http://www.headwize.com/tech/sshd_tech.htm

26. Brungart Sound Stage: Testing • Patented circuit • Time delay variability has yet to be tested • 300ms static delay • Redesign for time-delay control

27. Ohman Cross-Feed • Variable time delay and Cross-feed between Channels • Filtering and attenuation of signal inherent to circuit.

28. Ohman Cross-Feed http://headwize.com/projects/showfile.php?file=kemhagen_prj.htm

29. Ohman Cross-Feed: Testing • Cross-feed and attenuation sound good. • Variable Time Delay implemented on a oscilloscope test. • Time Delay not audible in hearing test.

30. Linkwitz Filter Cross-Feed • Built in variability of Time Delay and Frequency Boosts. • Time Delay circuit with cross-feed.

31. Linkwitz Circuit http://headwize.com/projects/cmoy1_prj.htm

32. Linkwitz Filter Cross-Feed: Testing • Works well on oscilloscope test • Linear time delay difficult to implement from the step time delay already implemented. • Sound quality in audio test greatly reduced.

33. Power Supply • Six 1.5 Volt Batteries • Voltage: -4.5V to +4.5V • AC/DC adapter input • Acknowledgement to Ken Uhlenkamp for his work on this project

34. Questions?