If you guys can't help me, I'm gonna have to build this thing :(

If you guys can't help me, I'm gonna have to build this thing :(

This is a discussion on If you guys can't help me, I'm gonna have to build this thing :( within the Off Topic & Humor Discussion forums, part of the The Back Porch category; My brother-in-law is, among other things, hard of hearing. He's to a point he cannot manage small hearing aids, much less the tiny filters and ...

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Thread: If you guys can't help me, I'm gonna have to build this thing :(

  1. #1
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    If you guys can't help me, I'm gonna have to build this thing :(

    My brother-in-law is, among other things, hard of hearing. He's to a point he cannot manage small hearing aids, much less the tiny filters and batteries. Still he needs to be able to hear. I ordered a hearing amplifier which is a headset thingy with a separate mic, etc., but it just wouldn't do the job, so I returned it.

    I wear hearing aids so I know about the upkeep and requirements, and I talked to my ear "doctor" and he couldn't come up with anything any better than I had tried

    Pretty much, as us guys lose our hearing, it is not just lowered hearing sensitivity, but we lose the highs, i.e. we don't hear the higher tones/frequencies but we can hear the lower ones pretty well. That really complicates things because just amplifying sound won't work - the lows will be too loud if we turn the volume up high enough to hear the highs.

    So here it is: if nobody can come up with something, I'm gonna have to design and build something. Well, l should say build, because I just finished the design and it simulates almost perfectly. It shows about 45 dB of gain plus a 10 dB boost for the "highs" with an increasing gain from about 400 Hz to 16 kHz.

    The tough part is I needed it to operate from two AA cells to minimize weight and bulk. A dry cell, be it alkaline or rechargeable, will exhibit a decline in voltage as it discharges, so designs have to account for this decay. AA cells start out at about 3V, (2.6V for rechargeables) so I figured to try to develop a circuit to operate at 2 volts before it starts failing.

    Here's what I came up with:

    It's possible that I could use low voltage op amps for the preamp and high boost circuits, but I have the transistors, don't have the op amps and I'm just not sure much would be gained by using op amps I have no experience with. I do know they would not simulate at all at 2 volts.

    This is the pre-amp and frequency boost developed around my favorite bipolar transistor amplifier circuit. One thing I like about it is simplicity, low current drain and high enough gain to exploit negative feedback gain stabilization and reduced distortion. Both stages are identical and I did add one touch to the basic circuit to improve gain and that is the RC bootstrap circuit from the output stage back to the driver transistor.



    The above circuit drives the next circuit and this was the real challenge: A class B push-pull power amp that will operate at 2 volts! This was totally my own creation. It took a couple of iterations, but I got it doing exactly what I wanted it to. On the simulator, I'm getting about a 1.6 volt peak to peak swing from a 2 volt supply. In case anyone is not familiar with just how challenging that is, the transistors have to split that 0.4 volt overhead which means each output transistor only has 0.2 volts to operate with - sort of



    I also added a bootstrap circuit for this section too, but not so much for gain, but to provide additional drive to the output transistor. Via the bootstrap circuit the voltage drive to the transistor is actually higher then the supply voltage.

    I probably should have changed some colors on the waveform simulation, but I got lazy. This is what an 8 kHz signal looks like driving a 32 ohm load.



    And, the following is a plot of gain (in dBs) versus frequency. Recall I wanted the gain to increase from about 400 Hz to 16 kHz. While this is not linear, it should do nicely. And this pic suffers the same as the previous, but the waveform of interest is the red curve. It shows the continually increasing gain as the frequency gets higher (bottom axis.



    I have most of the parts to start, but it's a loooong way from simulation to a working circuit and I'd rather find another solution, but I haven't been able to as of yet. So if somebody doesn't come up with something, I'm gonna have to start building. "Course it'd be a slick project and give me something to do to - as if I needed something to do.
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  2. #2
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    It's great that you're able to do that.
    You're operating above my personal noggin capacity.
    About all I'd be able to do to help would be to buy some "AA" batteries for you.
    Liberty Over Tyranny Μολὼν λαβέ

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    Member Array CrabbyOldGuy's Avatar
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    Crazy looking targets!

    Sorry, my schematic skills are way too rusty.

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    I'll loan him one of mine.
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    VIP Member Array Havok's Avatar
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    This is far beyond my comprehension. All I will say is good luck to you!
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    VIP Member Array dangerranger's Avatar
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    A friend uses a set of amplifiers that go in each ear and are programmed to receive a signal generated by his smart phone. It takes tones that he can't hear and puts them in tones he can. it also works in stereo. so you have a sense of direction. This also makes talking to him on the phone much easier. I'm almost sure he got these through the VA. That might be something to look for. Good Luck.DR

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    Senior Member Array M1911A1's Avatar
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    I suggest that you look into a plastic case in which to put it, that might hang about your brother-in-law's neck (or go into his shirt pocket), with a twisted-pair wire to a small in-the-ear 'phone such as the older hearing aids and mini-radios used.
    Maybe you could give him two separate circuits (perhaps on one power supply), one for each ear, with two separate ear-plugs. Each circuit could be tuned differently.

    In any case, a smallish plastic box could probably contain the circuit board(s) and a couple of batteries without much fiddling.
    Flipping the box lid open to change batteries would not necessarily imperil the circuit board(s).

    Helpful?
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    Tangle didn't change the colors on the waveform simulation!

    That's the only reason why I got a little bit confused.
    Liberty Over Tyranny Μολὼν λαβέ

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    VIP Member Array airslot's Avatar
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    Would something like this work? Pocketalker from Williams Sound
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  10. #10
    Member Array oldIthink's Avatar
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    You lost me at "my brother-in-law.

    Have you considered talking to the folks at Blue Parrot? Or one of the other remote phone headset company's. They can pack an awful lot of hardware and battery into an extremely small package.

    https://www.blueparrott.com/contact
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  11. #11
    Member Array Marc_Brooks's Avatar
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    Have you considered the eargo?

    https://eargo.com/
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  12. #12
    VIP Member Array bigmacque's Avatar
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    Quote Originally Posted by M1911A1 View Post
    I suggest that you look into a plastic case in which to put it, that might hang about your brother-in-law's neck (or go into his shirt pocket), with a twisted-pair wire to a small in-the-ear 'phone such as the older hearing aids and mini-radios used.
    Maybe you could give him two separate circuits (perhaps on one power supply), one for each ear, with two separate ear-plugs. Each circuit could be tuned differently.

    In any case, a smallish plastic box could probably contain the circuit board(s) and a couple of batteries without much fiddling.
    Flipping the box lid open to change batteries would not necessarily imperil the circuit board(s).

    Helpful?


    That actually should be helpful. My son was born deaf, and when he was very young - about 2 until he was about 10 or 11 we used an FM system in addition to his hearing aids. The receiver attached to him like a beeper on a belt with wires that ran up to his ears. You can't do FM with what you're designing, because you'd need a transmitter that everyone and everything else in the world used to transmit to the receiver; but the idea of a small case that clipped on the belt with the wired ear buds could work.
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    VIP Member Array Struckat's Avatar
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    Yes, I agree, but what is the S.D. for this load?
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  14. #14
    VIP Member Array G26Raven's Avatar
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    Tangle, you never cease to amaze me!
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    Distinguished Member Array Rabbit212's Avatar
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    Turn it up to 11!!!
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