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Looking for device to record phone audio

Hello:

In order to debug echo cancellation and DTMF keys, I need to record phone signals.

In my first attempt, I purchased an inexpensive adaptor, but the recorded audio has very poor quality. I am guessing that the cause is the ~50v. DC component.

A long time ago in this NG, I was given a very good recommendation. I was told to use an optical coupler which blocks the DC while passing all the sinusoidal signals.

Is there such device (not just an IC)? Any other alternative for recording phone signals?

TIA,

-Ramon F Herrera

Reply to
Ramon F Herrera
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for a basic coupler, use a 50K Resistor from the phone line going into a 1:1 audio xformer, have the other lead connect to the line via a cap for isolation of DC. use a pair of zener diodes around 2.5 volts or so back to back acrossed the input side of the xformer to protect the other side from the ring put an op-ampl on the output side of the xformer. the ring will be squared off at around 5 Vpp which could be used as a ring detector into a voltage comparator and the audio will be aprox 0.6 vrms.. i could be wrong there but i think that is close.

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Jamie

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