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Using A Phoneline
The above device permits the connection
of a household phone (and phone line) to a tape recorder or computer sound card
for EVP voice recording purposes.
The device input taps directly onto the
(undisturbed) phone connection wiring, with the output having a microphone (or
soundcard) audio plug via shielded cable.
When used in this way, the telephones are
used as a modified form of tape recorder microphone, so are for receiving EVP
voices as per the standard microphone method. A
faint background sound source may be useful with this microphone method -
perhaps a local radio tuned to static / low-level voice babble.
If there are two phones on the same line,
both may be used simultaneously (see later comments).
When used, the phone network supplies
power to energize the telephones when the handset is lifted, and the device then
channels the audio to the recorder or sound card.
Older models of telephone may work better
with this method, one reason being due to them having the older carbon
microphone, rather than the more modern electric version.
Circuit
Details
The two 100N caps connected to the line
are to isolate the phone line DC from the transformer, preventing any call
set-up requests to the phone exchange when the device is connected (phone
exchange will not sense this device). Device connects to red and green wires (in
USA) of phone termination. Do not remove any existing wires at termination.
The transformer provides balanced input
to unbalanced output, so the microphone plug can be grounded via the recorder
without upsetting phone line balance.
The 100K / 4K7 resistors drop the line
audio level so to be compatible with normal microphone input sensitivities.
The two cross-connected diodes ensure
that any ringing voltages do not damage the tape recorder (if the phone rings
while this device is connected the tape recorder wont be damaged).
Construction
A metal enclosure would be preferable to
avoid hum pick-up.
Shielded cable should be used between
microphone plug and the box and its components.The metal case (if used) should
be connected to the cable shield ground.
A couple of stand-alone
telephones can be energized locally to form a simulated network (see above
diagram) for experimentation. The output shown connects to the phone interface.
A 30V (approx) supply is used to energize
the phone, and this voltage is fed to the phone via two sets of relay coils and
resistors. The coils ensure that derived audio is not attenuated by the power
supply, and the resistors set the standing current flowing through the phones.
This current should be set to 30mA per phone. If preferable, the power supply
voltage can be altered instead, to achieve the 30mA.
The use of two telephones may provide
advantage over a single unit for the purposes of EVP reception, as there is a
circulating interaction of simultaneous audio currents between the two units,
which may aid reception.
The
two 2uF capacitors may not be needed if the above device only connects to the
interface unit - as the interface already has DC input blocking.
Content
from www.aaevp.com
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