Looking for device to record phone audio

[Ramon F Herrera]

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

 

[Jamie]

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

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.