Transcript Slide 1
Design Review Presentation Senior Design May06-01: Headphone Amplifier, Equalizer, and Sound Stage 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 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 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 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 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 Project Schedule Task Research Order Parts Circuit Design Circuit Implementation Circuit Debug Preliminary Testing Combinational Testing Final Circuit Choice Client Testing PCB Design Final parts order PCB order Case Mock-up Final Circuit Implementation Final Circuit Test/Debug Final Product Test Break Semester 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Finals Week 1-May 24-Apr 17-Apr 10-Apr 3-Apr 27-Mar 20-Mar Spring Break 13-Mar 6-Mar 27-Feb 20-Feb 13-Feb 6-Feb 30-Jan 23-Jan 16-Jan 9-Jan 2-Jan Winter Break 26-Dec 19-Dec Finals Week 12-Dec 5-Dec 28-Nov Thanksgiving Break 21-Nov 14-Nov 7-Nov 31-Oct 24-Oct 17-Oct 10-Oct 3-Oct 26-Sep 19-Sep 12-Sep 5-Sep 29-Aug 22-Aug None Semester 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 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 Circuits: Block Diagram S T E R E O I N P U T LEFT PREAMP LEFT LIMITER LEFT EQ BALANCE RIGHT PREAMP SOUND STAGE RIGHT EQ RIGHT LIMITER POWER SUPPLY The green lines represent components with ganged controls. The red lines represent power supply lines S T E R E O O U T P U T 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 Amplifier 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 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 Baxandall EQ • Five-band active equalizer • Single op amp per channel • Frequencies centered at (Hz): – 100 – 300 – 1k – 8k – 17k Baxandall EQ Band frequencies were found by the following formulas: f_bass = 100 Hz = 1 2 ( R5)(C1) 1 2 ( R6)(C 2) 1 f_mid = 1kHz = 2 ( R7)(C3 C5) 1 f_hmid = 8kHz = 2 ( R8)(C 4) 1 f_treble = 17kHz = 2 ( R9)(C 6) f_lmid = 300 Hz = http://headwize.com/projects/equal_prj.htm 1 2 ( R5)(C1) Baxandall EQ: Testing • 5-band still undergoing testing • Measure boost and cut • 3-band tested and works • Cut band nearly to zero when tested Resonant Frequency EQ • • • • Five-band redesign from three-band circuit Active One op-amp per band 10db boost / cut Resonant Frequency EQ (part 1) http://headwize.com/projects/equal_prj.htm Resonant Frequency EQ (part 2) http://headwize.com/projects/equal_prj.htm 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 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 Brungart Sound Stage Block Diagram http://www.headwize.com/tech/sshd_tech.htm Brungart Sound Stage Aural Specifications http://www.headwize.com/tech/sshd_tech.htm Brungart Sound Stage Time Delay http://www.headwize.com/tech/sshd_tech.htm Brungart Sound Stage Pinna Filter http://www.headwize.com/tech/sshd_tech.htm Brungart Sound Stage: Testing • • • • Patented circuit Time delay variability has yet to be tested 300ms static delay Redesign for time-delay control Ohman Cross-Feed • Variable time delay and Cross-feed between Channels • Filtering and attenuation of signal inherent to circuit. Ohman Cross-Feed http://headwize.com/projects/showfile.php?file=kemhagen_prj.htm 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. Linkwitz Filter Cross-Feed • Built in variability of Time Delay and Frequency Boosts. • Time Delay circuit with cross-feed. Linkwitz Circuit http://headwize.com/projects/cmoy1_prj.htm 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. 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 Questions?