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PostPosted: 30 Mar 2014, 21:56 
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Joined: 30 Mar 2014, 20:15
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Hello, I am starting a business and want to be able to record all of my phone calls (I am letting the callers know they are being recorded). I did a little research and found some products that are RJ11 to 1/8" jack and after looking at them it looks like its just a straight series connection I also found a schematic with caps in series with both the tip and ring of the phone line. So I tried to build one, I put a 22pF cap in series with both lines and plugged it into an old sound card ( I wasn't sure if the phone ringing would kill the card and it didn't) which worked. I now have it pluged into the mic of my main sound card and tried a few trial calls to and from my cellphone. I get a lot of feedback, outgoing voice can be faintly heard but the incoming is almost no-existent. Is there a way for me to get rid of the feedback and clean up the audio? Should I increas the value of the caps, or is the signal maybe too strong? Should I add a resistor in series to limit the current?


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PostPosted: 31 Mar 2014, 15:45 
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Joined: 30 Mar 2014, 20:15
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I should correct, I'm getting distortion not feedback.


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PostPosted: 31 Mar 2014, 19:13 
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Joined: 06 Jun 2008, 18:23
Posts: 4894
Location: Australia
wunderbred wrote:
Hello, I am starting a business and want to be able to record all of my phone calls (I am letting the callers know they are being recorded). I did a little research and found some products that are RJ11 to 1/8" jack and after looking at them it looks like its just a straight series connection I also found a schematic with caps in series with both the tip and ring of the phone line. So I tried to build one, I put a 22pF cap in series with both lines and plugged it into an old sound card ( I wasn't sure if the phone ringing would kill the card and it didn't) which worked. I now have it pluged into the mic of my main sound card and tried a few trial calls to and from my cellphone. I get a lot of feedback, outgoing voice can be faintly heard but the incoming is almost no-existent. Is there a way for me to get rid of the feedback and clean up the audio? Should I increas the value of the caps, or is the signal maybe too strong? Should I add a resistor in series to limit the current?

Never heard of doing any of this but I think the cap should be 0.1uf.

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PostPosted: 31 Mar 2014, 20:22 
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Thanks I will try this out, I had never heard of it before either, I thought I had to get an inline recorder but found this method.


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PostPosted: 31 Mar 2014, 22:16 
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Joined: 30 Mar 2014, 20:15
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I found a better schematic I made some minor changes, it uses a 1:1 transformer, mine is 150ohms. I have a .1uF cap in series with the tip from the phone and a 670ohm resistor in series with the ring of the phone, into the transformer, then 2 1n4001 diodes the 2nd diode is reversed from the first across the output. 0 distortion.

here is a lkink to the site, do a search for "Other transformer isolated interfaces"
http://www.epanorama.net/circuits/teleinterface.html


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PostPosted: 01 Apr 2014, 12:12 
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Location: Chilliwack, BC
ASCII art! :D

Epanorama must have scraped the content from Usenet ;)

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