AM modulator?

I like the idea of using the the vol control as an input to the AM radio. Be sure to capacitivly couple the iPod to make sure you don't get any DC into it from the radio and blow it up. The vol control is probably in the 500k to 1 Meg range, so the capacitors can be very small ( > .1uF is fine). I'd put one in series with each lead to totally DC isolate the external device from the radio.

Al
 
Here are my thoughts on interfaceing an MP3/CD box to an existing AM mono radio. L & R should probably be mixed together as shown so you can hear both channels. I haven't tried this yet, but it should work .... buyer beware . Hope this helps
Al
 

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Would these hook ups to the volume control use the radio to amplify the weak signal from the iPod or do they just run the iPod signal directly to the speaker? If so, the iPod wouldn't run the speaker with just 5-20mW of power unamplified.
 
B_man_Al said:
Be sure to capacitivly couple the iPod to make sure you don't get any DC into it from the radio and blow it up. The vol control is probably in the 500k to 1 Meg range, so the capacitors can be very small ( > .1uF is fine). I'd put one in series with each lead to totally DC isolate the external device from the radio.

Al
Click to expand...

Aren't you talking about diodes to isolate? Wouldn't capacitors in line block all current?
 
Old Henry ...

Yes the idea is to use the audio portion of the AM radio to amplify the weak signal from the iPod and drive the speaker .

The capacitors are used to isolate any DC that may (or may not be) present at the radio vol control from the AC audio signal coming from the iPod. The old vacuum tube radios had several hundred volts at various points in the circuit, which under a fault condition could appear at the vol control and potentially (no pun intended) blow up the externally connected iPod or CD player. There may also be smaller DC signals around the pot, which are produced from the audio signal itself, to control the receiver gain. THis feature is what tends to keep the strong and weak AM stations at the same vol level, even though the actual received AM signal may be 100's of times smaller or larger between stations.
 
Just to clarify the use of capacitors again, they allow AC signals (like the audio from an MP3 player) to pass through them while blocking any DC .
 
OK. I'm quite interested in this idea of playing a sound source through the radio as suggested and it looks like you know more about electronics and schematics than I do. So, here is the schematic of the 46-48 radio. The volume control looks a little different than yours. It seems to have two variable contacts. But, it also has wire colors. So, when you look at this schematic, which two wires would you splice the two leads from the external sound source to?
RadioSchematics.jpg
 
Old Henry ..

Your radio has a black and a brown on the vol control if I can read it .... my neck is getting a little sore :-) The black is on the top of the vol control schematic going to ground and the audio from the AM RF detector will be on the brown. Note this point will also have a small DC voltage present to control the AGC line (automatic gain control) so you must capacitively couple the external audio source as recommended.

Point A on my schematic will be connected to the brown wire (bottom lead of the vol ctrl, and B will be connected to the black or the top lead of the vol ctrl schematic.

I think this will work OK as shown, however the AM radio will still be connected into the circuit so you need to tune to a quiet spot on the dial (pretty easy these days) .


If its too noisy you will have to disconnect the brown wire from the pot and put it through a switch to prevent the AM radio signal from getting into and mixing with your iPod audio.

Make sure you don't disconnect the rest of the circuitry on the brown line (only to the pot) as this line controls the bias voltages to the RF section of the receiver.

Hope this works for you … let me know

Al
 
I had an MP3 port installed in my 1940 Ford Radio by a man in Ohio. He does this for a hobby so I cannot give his information out.

I looked at the connections and it appears that the MP3 plug disconnect the antenna and the out put of the player goes to the grid of the detector tube.
 
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