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hearing aids revisited

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by MrDEB, Nov 30, 2009.

  1. MrDEB

    MrDEB Active Member

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    Started playing w/ control voltage

    I may have stumbled on a method to control the audio peaks for front and back by adding a control voltage as seen in the attached screen shots
    a simple switch and V- supply, add a pot for adjustment
     

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  2. MrDEB

    MrDEB Active Member

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    forgot the schematic

    values etc need to be corrected?
     

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  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Instead of messing up the time constant of 3.9M R16 slowly discharging 0.1uF C7 with your low value pot to change the threshold voltage of the Jfet, instead change the value of R5. When R5 has a low value then the Jfet is cutoff most of the time and the max signal level will be higher. When R5 has a high value then the Jfet will attenuate signals at a lower level.

    The TL072 and most other opamps have a difficult job trying to drive a 600 ohm load. Their minimum spec'd load is 2k ohms.
    The 1N4001 is a high current rectifier for 60Hz. It works poorly at audio frequencies. Use 1N914 or 1N4148 signal diodes instead.
     
  4. dave

    Dave New Member

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  5. MrDEB

    MrDEB Active Member

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    Thanks will make changes.

    Contemplating using a pot for R5 for adjustment purposes only.
    The circuit will be the first stage
    second stage = tone control or bandpass filter
    3rd stage = a simple headphone amp using an op amp.
    I posted a schematic but its called a cmoy amp. Got from DIY audio
    HeadWize - Project: Designing A Pocket Equalizer For Headphone Listening (A HeadWize Design Series Paper)
    have two different tone controls I am simulating but still looking at the BP filters.
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Thanks for reminding me where the Baxandall 3-band tone controls circuit came from (National Semi LF353 datasheet). Lately I needed its frequency response graph and haven't looked at that datasheet for about 33 years.
     
  7. MrDEB

    MrDEB Active Member

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    I changed the value of R5 but not nearly the change of the pot in parallel of R16.
    Will play with the 3 tone control circuit with the peak limit circuit as an input.
    Found two different tone controls but feel maybe 3 band would be better?
     
  8. MrDEB

    MrDEB Active Member

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    The Baxadall looks better

    ran a comparison and the Baxadall looks better
     

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  9. MrDEB

    MrDEB Active Member

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    BY Joe I think I got it

    Here is hopefully the final design.
    Just need to build two individual circuits.
     

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