Hack Telephone to add Amplified Headset

AN-503 might be a good read too.

Cheers

Thanks!

_Might_ be up your way again... in discussions with DDC. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

In my last job, I used a Howland current pump across a resistor as the transmitter, then it was a rather simple matter to subtract the transmitted signal from the combined signal. The impedances were pretty critical (and nulled out) and echo cancellation software cleaned up the rest.

I?m sure Tomi Engdahl will have something:

Cheers.

--
Les Cargill

Wires are not cool. If you look at any display advertisement for computahs, telephones, or home electronics, you will find that there are no wires showing anywhere in the pictures. I can explain, but since you didn't like my explanation of how "cool" works, I'll first ask if you're interested.

Safety considerations prevent vendors from offering anything that is really loud. When placed against or in your ear, there is a real possibility of causing hearing damage. If you want threshold of pain type levels, you're not going to get it unless you sign a liability waver. This is also why you go to an audiologist before experimenting with high audio levels to compensate for hearing loss. You could easily make a mistake and make things worse.

However, you don't have to search very much to find devices that will do that. Just look for anything made for the hearing impaired or the average teenager.

Skype uses a much better codec than your local phone monopoly. Skype passes up to about 8KHz, while the phone company barely squeezes past

3.2KHz. If you want better quality, switch to a VoIP provider and use a codec with little or no compression such as G.711.

I had to think about that a bit. First, I couldn't find anything off the shelf that converts a $500 computer into a $10 telephone. In order to build such an abomination, the analog audio in/out from the computer would somehow need to interface with the POTS (plain old telephone service) line. It would need all the features of the $10 telephone including 4 wire to 2 wire conversion/isolation, sidetone, touch tone dialing, overdrive limiting to prevent crosstalk, a little frequency response tweaking, ring detector, etc. The interface box could be done by butchering a $10 telephone and somehow connecting the handset to the computer. When done, you have effectively duplicated the phone, turned the computer into a mic and earphone amplifier, and wasted much technology, time, and money on replacing a simple analog amplified handset.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Thus are separated the clueful from the foolish

snip

An important part of phone functionality is protecting the user from nearby lightning strikes. If you hook up to the phone's electronics you've just bypassed an important layer of that protection.

NT

"Landline" provider is Ooma, so it's VOIP. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

[snip]

Which suddenly strikes me that there are no protection issues AND the "line impedance" is known AND constant, so an Analog hybrid should be trivial.

(I'll battery power to avoid any "common" issues.) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Ooma Office or Ooma Telo? Are you using one of their HomePlug remote phone boxes in your system? Ooma has quite a few different devices and plans. Whatcha got?

Ooma service can have rather poor high end frequency response. Here's one complaint: The HD2 handset is mentioned but not a part of the problem.

I've installed a few Ooma Office and Telo boxes and agree with the complaint. The problem is that when you call another Ooma box, it connects via G.722 which is a high bandwidth, uncompressed codec. However, when you call a land line through the Ooma voice gateway, it uses iLBC (internet Low Bit Rate Codec) which is heavily compressed, royalty free, and cheap for Ooma to provide on their backhaul. So, if your the problem is at the gateway, there's nothing you can do at your end to fix the lack of high frequency response (except complain to Ooma or perhaps try Ooma Office). Based on voice quality, I have a suspicion (untested) that only the home Telo systems use iLBC through the gateway, and that Ooma Office service uses something better. I can test this if you're interested (next week pleeeze) as I have several customers using Ooma Office. So far the only complaint is that the 3rd line, which goes through an Ooma HomePlug power line networking box (forgot the model number) doesn't work with the fax machine and sometimes drops the call due to local power line interference from other offices in the building.

Troubleshooting Voice Quality

Also, try the Ooma speed test looking for jitter:

You might also try asking|complaining on the Ooma forums:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Ooma Telo.

But my sound quality issue dates before Ooma.

And my wife, using the same phone, hears just fine...

So I just need to add gain, and perhaps, compensation.

Download Speed: 25539 kbps (3192.4 KB/sec transfer rate) Upload Speed: 11983 kbps (1497.9 KB/sec transfer rate) Latency: 36 ms Jitter: 1 ms

3/15/2016, 9:24:29 AM

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142     Skype: skypeanalog  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Take a look at the TCM3105 data sheet/app notes for a op-amp hybrid.

Steve

Thanks, Steve! ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Ok, it's your hearing. There are a variety of online hearing tests available. I found them useless about 4 years ago and haven't tried them since. A few produce a tolerable graph of your hearing compared to what would be expected for your age. That will tell you what frequency range needs boosting, which ear, and possibly how much. Beware of any site that demands personal information before it will let you run the test: I just ran this one: which says I have a -15db loss @4KHz (compared to lower frequencies) in both ears. However, the test stops at 4KHz, which might be a problem if you have trouble hearing music.

I still would suggest a made for the purpose amplified handset for your antique phone. Something like this: For amplifying just the handset audio, you don't need to design a hybrid, deal with isolation, sidetone, lightning protection, etc. Just and and maybe some high frequency boost.

That's totally normal and should work just fine. Plenty of bandwidth and little jitter.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558