Design Review Presentation

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Design Review Presentation

• Senior Design May06-01
• Headphone Amplifier, Equalizer, and Sound Stage

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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

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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

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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

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Functional Requirements Cont'd

• Casing
• 8x8x2 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

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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

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Project Schedule
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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

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Circuits Block Diagram
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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

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Amplifier
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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

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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

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Baxandall EQ

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

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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
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Baxandall EQ Testing

• 5-band still undergoing testing
• Measure boost and cut
• 3-band tested and works
• Cut band nearly to zero when tested

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Resonant Frequency EQ

• Five-band redesign from three-band circuit
• Active
• One op-amp per band
• 10db boost / cut

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Resonant Frequency EQ (part 1)
http//headwize.com/projects/equal_prj.htm
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Resonant Frequency EQ (part 2)
http//headwize.com/projects/equal_prj.htm
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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

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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

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Brungart Sound Stage Block Diagram
http//www.headwize.com/tech/sshd_tech.htm
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Brungart Sound Stage Aural Specifications
http//www.headwize.com/tech/sshd_tech.htm
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Brungart Sound Stage Time Delay
http//www.headwize.com/tech/sshd_tech.htm
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Brungart Sound Stage Pinna Filter
http//www.headwize.com/tech/sshd_tech.htm
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Brungart Sound Stage Testing

• Patented circuit
• Time delay variability has yet to be tested
• 300ms static delay
• Redesign for time-delay control

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Ohman Cross-Feed

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

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Ohman Cross-Feed
http//headwize.com/projects/showfile.php?filekem
hagen_prj.htm
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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.

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Linkwitz Filter Cross-Feed

• Built in variability of Time Delay and Frequency
  Boosts.
• Time Delay circuit with cross-feed.

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

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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

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Questions?