Mirco UHF hearing AID Circuit.

[Audioguru]

If you read the datasheet and look at the amplifier schematic for the LM4911 stereo amplifier you will see that it has three amplifiers, not just two.
The third amplifier provides a reference of half the supply voltage for the earphones so that large output coupling capacitors are not needed to block DC.
Any amplifier using a single polarity supply makes a loud POP in the transducer when it is turned on or off. The LM4911 amplifier has a click and pop reduction circuit that needs a capacitor or the controller circuit can do it. I do not know why it has a shutdown mode instead of simply turning it off. Maybe the controller can make it shutdown when you say, "Shutdown!"?

The terrible frequency response of hearing aid balanced armature transducers is made normal with an equalizer that is needed anyway to adjust the response to the deaf person's hearing problem. Some people have frequency notches that must be boosted and other people have frequency peaks that must be reduced. Many people have both. Usually the equalizer in a hearing aid is digital so setting it up is simple and accurate. A hearing aid amplifier circuit also has compression so that very loud sounds have their level reduced to normal and very weak sounds are automatically boosted.

 

[D.A.(Tony)Stewart]

for BTE type hearing DIY crystal earphones can be made with 200~4000 Hz response, 20k impedance. So if power efficiency is crucial, you might rethink your requirements.

Piezoelectric earphones also known as crystal earphones are the most sensitive earphones. In fact they are at least 10 times more sensitive than very sensitive magnetic earphones, dynamic earphones, and electrostatic earphones. Sensitive earphones have a very high impedance, which is measured in ohms.

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If you read the datasheet and look at the amplifier schematic for the LM4911 stereo amplifier you will see that it has three amplifiers, not just two...

Which means no output cap is required for stereo and if just mono earphone, any stereo amp with differential output can be capless on output as well.

 

[illusionists]

Actually I was confused by Chinese advertising & mentioned UHF.

Oh, ok audioguru.Nice to know that aswell.

Piezoelectric earphones ◀ Size matters in our case broda.

Oh ok. Ok brodas, just as final approach, tell me what all parts to order (components).Getting too much hyper on making one and share with ya all. Oh, the youtube video will have credits of all of your name and link . Also I had seen few videos where they shown on how to make that small pcb using copper etching method.

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A bit offtopic:- youtube this channel "John Hutchison" I've been following him from many years. I'm sure you people will get an good entertainment too, he's bit funny sometimes. Usually he wont provide his chat iM, in very exceptional case he will provide. And I'm one of them, nice guy to speak with over skype. Simple living. Though he don't be over IM's mostly. But when he is, he never forgets to say hello to his dear ones. That guy is multi talented in all fields.

 

[D.A.(Tony)Stewart]

Is Hutchison still playing with magnets? The Japanese didn't come home with anything useful after visiting him.

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Compare your design goals with the best ( who also used inner ear piezo transducers in some models)

https://www.rion.co.jp/dbcon/pdf/A_series-E.pdf
https://www.rion.co.jp/asp/product/communication/ProA.asp?pos=H2&div=1&st=&pr1=&pr2=&gr=
https://www.rion.co.jp/english/products-e/communication/faq-e.html#Q7

You'll notice that only the body worn (MP3 player like) are the best for most acute hearing loss i.e. the best quality

https://www.rion.co.jp/english/products-e/communication/products_level-e.html

 

[illusionists]

Nice to know that you too know him somehow @ sunny. Actually Hutchison is working on free energy these days. He had sold free energy devices to few Japanese industrialist and few of the world's biggest defence contractors, I guess that. He will surely make the free energy concept available to public @ free of cost.But its just an perfect time he is waiting for. That guy has lot's to disclose ,but few things are good if kept secret for long,else they can harm human kind or maybe their misuse can bring devastating results.


Even i'm somehow related to aliens stuff,but i dont want officials eye on me and get me into trouble.If you insist then i might open an new thread on this and share my experiences. But the day i do that,one thing sure.It will be on news and all over web articles.The things never spoken before.Only the real ones will know what i'm saying and judgement my statements.

Will check that piezo one.

Edit:
Oh they are ready made one's. But was an good read with respect to different available types.

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@ 'Audioguru' :- This 3 rd one of LM4911 https://www.ti.com/lit/ds/symlink/lm4911.pdf

,Well simulate an circuit with stable gain.Will order parts after this and start the work.


& guy's for our earpiece mould,i have an idea .I will be using heat shrink pipe for that.How z that,let me know if there's anything better than this.

 

[Audioguru]

You said the "hearing aid" will be used by people who have normal hearing. Why?
You said it will use a telecoil instead of a microphone. Then how will you prevent pickup of 50Hz mains hum?
Do you already have a loop of wires around a room that is driven from a power amplifier?

The LM4911 stereo circuit shown has a gain of 1. You also need two preamps with a gain of from 40 to 200.

 

[illusionists]

Yes, normal people use. We can use for covert operation.

Yes, I had made an loop. lm 386. Instead of speaker I attached enameled wire with 60 turns.

Lol.it has gain of 1. Lol. Oh man, adding that wont increase the size of our earpiece? Just thrown in some proper circuitry man. Oh yesterday when I went market to buy veggie, I bought water soluble flux (lead and acid free , I guess). Also got an small tube of smt solder paste. This solder paste, so little and cost as double of solder flux. Anyways. Hm

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Also when I saw the earpiece circuit, I just saw one IC with 3 pin one side and 3 pin other side. Total 6 pins. And 4 caps and 2 transistor I guess.

 

[Audioguru]

Yes, normal people use. We can use for covert operation.
Yes, I had made an loop. lm 386. Instead of speaker I attached enameled wire with 60 turns.

You do not understand that a high current from an amplifier with high output power is needed to produce enough electromagnetic energy in the coil for your telecoil to pick it up. The output power from a little LM386 is almost nothing.

Lol.it has gain of 1. Lol. Oh man, adding that wont increase the size of our earpiece?

Its specs for low distortion and a full audio bandwidth are with a gain of 1. You can increase the gain up to 1000 times but the distortion and hiss will increase and the high frequencies will be cut.

Also when I saw the earpiece circuit, I just saw one IC with 3 pin one side and 3 pin other side. Total 6 pins. And 4 caps and 2 transistor I guess.

The datasheet for the LM4911 shows that it has 10 pins and shows how to connect them.

 

[D.A.(Tony)Stewart]

Earbud efficiency is not a trivial task.

It takes very fine wire.... >AWG 48 with hundreds of turns, samarium cobalt magnet and a good diaphragm.

- for 200 Ohms @300Hz is 100mH
- for 50 Ohms @300Hz is 25mH

 

[illusionists]

@ audiog,
The actual earpiece currently sold on market utilizes LM386 as an audio op-amplifier,i had seen it with my eyes.

yes,i agree that LM4911 got 10 pin's.Actually i said about the actual micro earpiece IC which is being sold on market.

@Sunny,ofcourse yes agree with that.

I can clearly read on that SMT IC :- LM386-N

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small correction "The actual earpiece currently sold on market " <- i mean the neckloop

 

[illusionists]

So may i have simulated circuit for the earpiece???

 

[Audioguru]

The Bluetooth receiver is huge. So of course it uses an ordinary LM386 power amplifier to drive a small speaker or ordinary headphones.
You talk about a tiny "earpiece" with all the electronics and the transducer inside it and using a telecoil to receive a magnetic signal, not using Bluetooth UHF radio signal.

I cannot simulate the circuit without the circuit design being finished but the design is barely started. I think it will sound AWFUL and its performance will be TERRIBLE because it will be old fashioned. A tiny modern digital hearing aid is programmed for the person's hearing and for the transducer.

 

[illusionists]

No problem if its old fashioned. We don;t need an HI-FI precision,we will create an base and later others can improve it on their own skills

But at least we must have an base circuit.desperately waiting for your input .Thanks

 

[Audioguru]

Since you do not know anything about electronics then you should do gardening instead.

 

[illusionists]

Yes agree i don't know anything about electronics.

But ,no this gardening statement doesn't suits well on me @ Audioguru because i'm not an Electronic Engineer (I had mentioned in my first post itself) .So its not valid in my case.

I'm just an beginner hobbyist in electronics.

I hope you or others from here help in providing earpiece circuit so that i can start the work and contribute and new base to all hobbyist and electronic engineers.

Always remember,sharing is caring. When we die we have nothing to take with us except blessings

 

[Audioguru]

Since you are a beginning hobbyest then why don't you start with a project that you can put together by yourself and obtain normal size parts that are available in your country?
Use an LM386 amplifier IC and a speaker. First use an MP3 player as its input then increase its gain as shown in its datasheet and try a microphone. The next step would be trying a coil around the room driven from a power amplifier and a coil at the input of your amplified speaker.

After you have those normal parts working properly you can try it with the tiny parts you have been talking about to see all the problems caused by the very small sizes.