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This is a sub-selection from Phone line amplifier?

aurgathor
join:2002-12-01
Lynnwood, WA

1 recommendation

aurgathor to cowboyro

Member

to cowboyro

Re: Phone line amplifier?

said by cowboyro:

I want to use multiple phones in the house. While hacking one is acceptable, when I'm considering 6 phones it's no longer OK.

I see. For that much of a load, you probably need an amplifier.

I was hoping lutful will post a transformer-less DSP solution -- but he seems to be slacking....
Apparently, there are some patents on them, so they do exist, at least in patents.

I think you can scavenge hybrids from phones or from modems -- just go to some thrift shop.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

1 recommendation

lutful

Premium Member

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said by aurgathor:

said by cowboyro:

I want to use multiple phones in the house. While hacking one is acceptable, when I'm considering 6 phones it's no longer OK

I see. For that much of a load, you probably need an amplifier.

I was hoping lutful will post a transformer-less DSP solution -- but he seems to be slacking....

I was waiting for someone to actually post a convoluted analog POTS interface circuit that manipulates just the audio without impacting ring waveform and off-hook detection. Good quality telephony devices designed since 2005 actually use transformer-less POTS interface and include DSP.

Above block diagram shows how you can make a digital FXS-FXO repeater using off-the-shelf SLIC/DAA ICs and a DSP or FPGA that could do any kind of manipulation of the audio and DTMF. But AFAIK such a device does not exist but VoIP gateways that also have a proper FXO interface could be hacked to do this job.

cowboyro See Profile ... If the Magicjack is connecting to all the phones in the house, the "ring equivalent number" or REN seen by their line driver IC could be too high.

Jason
Stowage Class Traveler

join:2001-01-24
38.2967 Lat

Jason

But aren't most modern phones (with a wall-wart power supply) typically ridiculously low REN?

I just looked at my base, and it lists 0.1 REN

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to lutful

Premium Member

to lutful
said by lutful:

cowboyro See Profile ... If the Magicjack is connecting to all the phones in the house, the "ring equivalent number" or REN seen by their line driver IC could be too high.

That's never the case with modern phones. And it's usually one base with multiple handsets...
I put the scope on the line and the incoming sound from the echo test number is ridiculously low compared to the outgoing level, so that rules out any issue with the phone.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

1 recommendation

lutful

Premium Member

Typical VoIP ATAs can't easily drive the convoluted wiring that go with having too many phones. By contrast, Telco port has a very robust line driver ... but your audio spectrum is still being attenuated.

Anyway, you will need to detect off-hook status to insert and remove the audio equalizer/amplifier device in the phone line.
public
join:2002-01-19
Santa Clara, CA

public to aurgathor

Member

to aurgathor
said by aurgathor:

a transformer-less DSP solution

I think you can scavenge hybrids from phones or from modems -- just go to some thrift shop.

A hybrid can be realized with two op amps. No dsp needed.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

Click for full size
said by public:

said by aurgathor:

a transformer-less DSP solution

I think you can scavenge hybrids from phones or from modems -- just go to some thrift shop.

A hybrid can be realized with two op amps. No dsp needed.

Just a bit more than that. See above complete schematic from Clare app note. FYI the dsp core comes as a baggage in modern telephony chipsets which incorporate the hybrid. See earlier block diagram from Silabs sales material.

*** Question to all the "hybrid" proponents ... are you suggesting putting two hybrids back to back and amplifying the audio using the hybrid's TX/RX op-amps? Or are you talking about the "hybrid" boxes used by radio stations to put callers on the air? There is a huge difference.

aurgathor
join:2002-12-01
Lynnwood, WA

aurgathor

Member

said by lutful:

*** Question to all the "hybrid" proponents ... are you suggesting putting two hybrids back to back and amplifying the audio using the hybrid's TX/RX op-amps? Or are you talking about the "hybrid" boxes used by radio stations to put callers on the air? There is a huge difference.

Methinks the answer should be pretty obvious from the original question and the answer given.