Hi,
So a brief backstory, I know just enough about electronics to be dangerous, but to be honest I have stayed away from RC/LC circuits, Q-power, resonance, and the like unless I'm following a schematic where the magic is already done for me. The second thing is I'm damn near deaf. This brings me to the the reason why I'm here.

Due to my hearing regular headphones don't do squat. I buy "loops" that are quite expensive that use inductive coupling to change the audio to an EMF signal that is picked up by a coil in my hearing aids. They are as small or smaller than standard headphones, and typically loop around my neck instead of speakers over my ears. They come in active and passive designs. I have an expensive active "loop" that is magic. sounds incredible, powerful, high fidelity, etc. I use that at home. I also have an entirely passive "loop" that I use for any work, sweat, outdoors, water, etc. You get the idea. It is still expensive.

After having many issues with the passive loop and tired of ghetto repairs I finally put it out of it's misery and tore it open to see what was inside and was completely shocked. I could make this myself, for a mere minute fraction of the cost. In fact I did make one. I copied the original design with components I had lying around, and it sounds okay. I want to better understand the design so I know what parts to tweak and my main goal here is to remain PASSIVE and have as high of FIDELITY as possible. This is hard for me because I don't have a true L meter or a legit way of measuring impedance. I also don't quite understand how the components affect the circuit and where my tweaking should start. Additionally, with my hearing it is hard to tell what is wrong, I can just tell I need to change components. I have tweaked quite a bit but still land just below the retail version in terms of fidelity. I could be satisfied with what I've brewed up, but I know there is a science behind here that with the right information I could make something that sounds as good as, if not better than the expensive retail version, that judging by the soldering alone is a hack job..

So at the input is a 3.5mm mono jack usually plugged into my phone. Can you help me understand this bare bones circuit? I assume the cap is used as a standard DC blocking cap and anything from 20uf-100uf is preferable to block DC but still give me adequate lower response. In my toying around, a direct short gives me horrible audio distortion, but it still works. I honestly cant tell much difference between 100uF and 470uF except that it starts to sound muffled if I go higher than 100uF, and anything lower than 10uF has some audio issues, but I don't have a huge assortment of electrolytic caps to try. The toroid coil I hand wound a few times, seems like more coils equal more amplitude, and there is a finite zone of effectiveness. Too small and it doesn't couple well enough for me to pick up the audio unless I hold the loop by my ear. Same goes for too large, and/or too few wraps. Does the loop's wire play into this? Should I be trying a different gauge? What is the balance here? Are there other PASSIVE electronics you think I should try? Is there a magic impedance I need to shoot for? Essentially it seems like a voice coil but instead of moving a magnet I'm moving electrons in a wire. How can I get this to have as high fidelity as possible, with adequate power? Where should I start to deconstruct this circuit? Thanks for reading my wall of text and looking at my paint drawing The coil at the bottom right is pretty much identical to what I've wound and works well. Your input is much appreciated!

 

Can you post pictures of the device in question?

 

Can you post pictures of the device in question?

 

You might try a larger magnetic core and see if that makes a difference.

The wire size is likely not a large factor here. Generally you use as small a wire as you can conveniently handle.

 

Breadboard with coil I wound. 100uF cap.

 

You might try a larger magnetic core and see if that makes a difference.

The wire size is likely not a large factor here. Generally you use as small a wire as you can conveniently handle.

I assume you're talking about the winding and not the loop, correct?

 

I assume you're talking about the winding and not the loop, correct?

Not sure I understand the question.

 

This may have some background:
http://archive.siliconchip.com.au/cms/A_112366/article.html

Also, you could increase the coupling by increasing the number of turns around your neck. This could be done if you could find some thin multicored cable and wired it as a multiturn loop.

 

Hi,
So a brief backstory, I know just enough about electronics to be dangerous, but to be honest I have stayed away from RC/LC circuits, Q-power, resonance, and the like unless I'm following a schematic where the magic is already done for me. The second thing is I'm damn near deaf. This brings me to the the reason why I'm here.

Due to my hearing regular headphones don't do squat. I buy "loops" that are quite expensive that use inductive coupling to change the audio to an EMF signal that is picked up by a coil in my hearing aids. They are as small or smaller than standard headphones, and typically loop around my neck instead of speakers over my ears. They come in active and passive designs. I have an expensive active "loop" that is magic. sounds incredible, powerful, high fidelity, etc. I use that at home. I also have an entirely passive "loop" that I use for any work, sweat, outdoors, water, etc. You get the idea. It is still expensive.

After having many issues with the passive loop and tired of ghetto repairs I finally put it out of it's misery and tore it open to see what was inside and was completely shocked. I could make this myself, for a mere minute fraction of the cost. In fact I did make one. I copied the original design with components I had lying around, and it sounds okay. I want to better understand the design so I know what parts to tweak and my main goal here is to remain PASSIVE and have as high of FIDELITY as possible. This is hard for me because I don't have a true L meter or a legit way of measuring impedance. I also don't quite understand how the components affect the circuit and where my tweaking should start. Additionally, with my hearing it is hard to tell what is wrong, I can just tell I need to change components. I have tweaked quite a bit but still land just below the retail version in terms of fidelity. I could be satisfied with what I've brewed up, but I know there is a science behind here that with the right information I could make something that sounds as good as, if not better than the expensive retail version, that judging by the soldering alone is a hack job..

So at the input is a 3.5mm mono jack usually plugged into my phone. Can you help me understand this bare bones circuit? I assume the cap is used as a standard DC blocking cap and anything from 20uf-100uf is preferable to block DC but still give me adequate lower response. In my toying around, a direct short gives me horrible audio distortion, but it still works. I honestly cant tell much difference between 100uF and 470uF except that it starts to sound muffled if I go higher than 100uF, and anything lower than 10uF has some audio issues, but I don't have a huge assortment of electrolytic caps to try. The toroid coil I hand wound a few times, seems like more coils equal more amplitude, and there is a finite zone of effectiveness. Too small and it doesn't couple well enough for me to pick up the audio unless I hold the loop by my ear. Same goes for too large, and/or too few wraps. Does the loop's wire play into this? Should I be trying a different gauge? What is the balance here? Are there other PASSIVE electronics you think I should try? Is there a magic impedance I need to shoot for? Essentially it seems like a voice coil but instead of moving a magnet I'm moving electrons in a wire. How can I get this to have as high fidelity as possible, with adequate power? Where should I start to deconstruct this circuit? Thanks for reading my wall of text and looking at my paint drawing The coil at the bottom right is pretty much identical to what I've wound and works well. Your input is much appreciated!

View attachment 137935

It might have been Everyday practical Electronics that published articles and projects for a public venue hearing loop.

A toroid is pictured - the whole point of a toroid is immunity to external magnetic fields.

IR is an alternative, but requires modulating the IR beam and decoding it at destination.

 

Can't say I am much help, but I'd love to hear how this thread develops.

Back a number of years, I tinkered with a large hall loop system, basically wired directly into a (cheap) power amplifier. We ended up using 8 winds around the hall to boost the signal & (supposedly) to increase impedance so it wouldn't stress the amplifier as much. Biggest flaw in the signal was what seemed like higher dynamic range in the higher frequencies (it hurt my ears). The owner lost patience with my tinkering, and so we left the project the way it was--functional & with reasonable quality, but I wasn't satisfied with the sound...

 

I guess your hearing aids sound good like mine do. I guess you want to use them as headphones so that the sound from speakers does not disturb people nearby.
My hearing aids detect the magnet in a phone or on a phone that I mount a magnet then they switch to play phone sounds in both earphones and with telephone quality (no bass and no highs). So I do not want to try your loop idea.
My hearing aids came with a Bluetooth transmitter that I am supposed to feed audio signals then my hearing aids play the sounds. But my hearing aids boost and play only high frequencies that my age (72) has reduced so the sounds are without any bass.

The capacitor feeding your loop is getting AC so it must be non-polar, most electrolytic capacitors are polarized for DC only but some are made non-polar. If your capacitor is polarized then it rectifies and distorts the audio.

 

It might have been Everyday practical Electronics that published articles and projects for a public venue hearing loop.

A toroid is pictured - the whole point of a toroid is immunity to external magnetic fields.

IR is an alternative, but requires modulating the IR beam and decoding it at destination.

This is true, but it is also the basis of how the system works! I could be confused or mistaken but I believe a toroid is so effective because it contains the EMF within the core, which is why it is popular in power supplies as all stray EMF is isolated. Which is exactly how this works, the signal is fed to a toroid essentially converted to an EMF field in the center of the toroid. SInce the "loop" goes through the center of the toriod, the audio is coupled quite well. Any other type of wrap would not work nearly as well. Either way, I removed a toroid from the original retail device, and I hand wound a toroid, and both are definitely a toroid, and couple the audio amplitude well. Just fidelity is lacking!

 

Not sure I understand the question.

I'm assuming you mean the wraps around the toroid and not the loop of wire through the center of the toroid?

 

I guess your hearing aids sound good like mine do. I guess you want to use them as headphones so that the sound from speakers does not disturb people nearby.
My hearing aids detect the magnet in a phone or on a phone that I mount a magnet then they switch to play phone sounds in both earphones and with telephone quality (no bass and no highs). So I do not want to try your loop idea.
My hearing aids came with a Bluetooth transmitter that I am supposed to feed audio signals then my hearing aids play the sounds. But my hearing aids boost and play only high frequencies that my age (72) has reduced so the sounds are without any bass.

The capacitor feeding your loop is getting AC so it must be non-polar, most electrolytic capacitors are polarized for DC only but some are made non-polar. If your capacitor is polarized then it rectifies and distorts the audio.

Thanks for your response. I'm wondering if your hearing aids are not programmed like mine, or??? Mine also automatically switch with a magnet nearby but they also sound really good in that mode. My more expensive neck loop that has alot of circuitry and a small internal battery (full package is much smaller than an altoid tin) sounds great. Full highs, full lows, it has everything I need out of a neck loop, only thing it lacks is actual bass vibrations to buzz my bones.

The simple and fully passive/analog neckloop is what I'm trying to improve on. The retail version literally consists of a single 100uF cap and a toroid in which the neck loop goes through the center of. The amplitude is good, and the fidelity is decent. I have made some copy-cat versions and it works well, the fidelity falls JUST short of the retail version, but all of mine I built for free. It definitely has a tinny sound, and lacks low end and just sounds like its missing depth.. I'm trying to understand how the circuit works and what direction I need to go to couple the audio to the wire around my neck in the best way, and by best I mean fidelity. I'm still lost as to how the actual circuit works, i get the basics, (toroid converts to EMF which the loop picks up and my hearingaids pick up the loop) but I don't know how to get better sound quality. How do I couple audio to a copper wire and keep it as effective and original as possible? Keep in mind the "telephone" mode of my aids are definitely without a doubt capable of high quality audio.

-With that note, I did try a non-polarized cap, in which I used 2 100uF caps back to back, resulting in roughly 50uF unpolarized and the audio quality definitely improved. Definitely better than a polarized 50uF cap, I would say the fidelity is on par with the original in this configuration, without a doubt. Now what else can I do, how can I couple the audio even better? The small "expensive" neckloop does it incredibly well, and is still unnoticeable under a T-shirt. I would tear that one open but it cost me more than a couple hundred and honestly works so well I am unwilling to crack it apart. I really want to know what direction I need to head, and I sure some minds here can decode this ridiculously simple circuit!

 

Also, I guess if need be I couple experiment with adding power to the equation if someone knows a direction to head. Ideally I would keep it passive but if some gates, transistors, buffers, or what have you need some power, I could breadboard it and see. In the end I need to know how my expensive neckloop manages to couple the audio so cleanly to a simple copper wire around my neck. If I can improve fidelity just off the power coming from the headphone jack from my phone, I would be elated!

 

how can I couple the audio even better?

Try much higher value capacitors, say 1000uF (non-polarised). That should let more bass through.