On 8/30/07 5:48 PM, in article
[email protected],
On 8/30/07 1:25 PM, in article
[email protected],
Hello Don,
Thanks for your time and your sage advice. Take a look at the images
of
the
board for the radio and let me know what you may make of them per the
following...
If your AM radio uses an audio output transformer, find the
connections
from
it to the speaker, and see if both wires go directly to the speaker.
If
they don't then one of them is probably connected to the systems
"common"
somewhere. Connect it to the shell of your male RCA jack. If one
is
not
connected to common, connect it to the shell of your male RCA jack.
//SpeakerWire
http://metromilwaukee.com/images/radio/speakerwire.jpg
//ObliqueView
http://metromilwaukee.com/images/radio/obliqueview.jpg
//TopView
http://metromilwaukee.com/images/radio/topview.jpg
<%= Clinton
On 8/30/07 9:42 AM, in article
[email protected],
I like to record the Coast To Coast AM radio program which airs on
local
radio from 12am to 5am nightly. I have a TV-VCR combo that will
support
recording an external source.
In the front of the TV-VCR there are two female RCA [1] inputs,
one
input
labeled Video and the other input labeled Audio. In the rear of
the
TV-VCR
there are -- two pairs -- of RCA inputs, one pair labeled Audio in
and
Audio
out and the other pair labeled Audio in and Audio out.
I know I can set the TV-VCR to Line 1 to record input from an
external
device. Can somebody help explain to me how to wire the speakers
(output)
of
an AM radio to interface with the TV-VCR to enable recording radio
programming (input) to the VCR?
<%= clintonG
[1]
http://en.wikipedia.org/wiki/RCA_connector
Okay searching the web I just learned the speaker wires transmit
power
and
not a 1:1 audio signal as I ignorantly presumed.
The speaker wires carry an audio signal (an AC voltage) to a low
impedance
speaker (probably about 8 Ohms). The speaker impedance (similar to,
but
more complex than resistance) presents a load on the voltage,
producing
a
current flow in the speaker wires. The product of the voltage and
current
is power.
Forum discussions say I
must use an amplifier inline i.e. AM radio speaker wires -->
amplifier -->
TV-VCR Audio In.
Your forum discussion group is, in my experience, wrong on this one
I don't really understand how power can become audio when amplified
You should discard this idea. Further study, if wanted, will
explain
the
conditions much better.
but if
that's all that it is I know I am using an older table top AM-FM
radio
which
will need to have an amplifier to record the radio's audio using
the
TV-VCR.
No external amplifier is needed.
Your recorder's audio input has a very high impedance, which means
the
signal audio voltage will drive it easily.
If your AM radio uses an audio output transformer, find the
connections
from
it to the speaker, and see if both wires go directly to the speaker.
If
they don't then one of them is probably connected to the systems
"common"
somewhere. Connect it to the shell of your male RCA jack. If one
is
not
connected to common, connect it to the shell of your male RCA jack.
Connect one end of a low power, 100,000 Ohm resistor (radio shack?)
to
the
other speaker wire. Connect the other end of the resistor to the
center
pin
of the RCA jack.
Turn the radio volume down low, and plug the RCA jack into the audio
input
of your recorder. While recording, turn the radio volume up to a
usable
level.
So what might be your recommendation for the least expensive
amplifier?
I'll
be calling Radio Shack to learn what may be learned. Thanks for
your
time...
<%= clintonG
I can't tell if the transformer shown is a power transformer or an
audio
output transformer. If you can't trace the wire by eye, or check it
with
an
Ohmmeter....... Hmmm!
Do you have a Volt/Ohmmeter? If yes, then first measure for voltage
(AC
and
DC) between the outer shell of the audio input jack, and each of the
radio
speaker wires. If there is no voltage, then measure for resistance
between
the same points. If there is no voltage and no continuity (n low
resistance) then it doesn't matter which wire goes where.
Otherwise..... Do you have a soldering iron?
Have soldering iron and good at soldering but no meters.
Ok. Won't need soldering iron then.
What does the large
obstructive metal shield wrapped around the transformer imply?
That there is a honking big get-hot transistor mounted on it, needing to
shed it's heat to the surroundings.
Load the
SpeakerWire.jpg and ObliqueView.jpg links above. Any inference
regarding
the
determination of transformer type which may be deduced?
No, I can't see enough detail to be sure. If you can't see if the
speaker
wires are connected to it (or that the AC power is wired to it via the
power
switch), let's ignore it.
Your comments
regarding my reply to a headphone hack as suggested by Meat Plow?
Doesn't
sound plausible or consistent with what I've learned from your earlier
comments. Jees, this topic deserves to be blogged for posterity!
Actually, if you could put in a jack that opens the path to the speakers
when a plug is inserted, that would be ok and you might like it because
the
speakers would be off while you are recording. Or just add a jack in
parallel with the speakers, but the speakers will be on while you
record.
A jack is optional hardware. However, see below.
Since we have no schematic, no meter, and don't know how the amplifier
output interfaces the speakers, and don't know whether the radio or
recorder
is AC/DC, there is a safety hazard in going further with the simple
plan.
Instead, go to radio shack and buy their el-cheapo 8 Ohms to 1000 Ohms
audio
transformer. Connect the 8 Ohm connections to the speaker wires (with
or
without a jack), and connect the 1000 Ohm transformer wires to the RCA
plug
for connection to the recorder. That is not only safe, but the quality
of
the sound may be a bit better.
