Going to try and modify my mono AM radio to take a mp3 input and output stereo. In addition, I want it to light up, turn on and off with the existing knob, and control the volume with the existing knob. This should be fun.
Here are some before pics of the radio.
Click above for a video of the inside and the tuner moving, (wmv)
I took it apart in order to get to the on/off/volume knob. Was a little tricky, the thing is built like an airplane black box.
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This is the volume/on/off switch that I was after. It is a Philco. The part number is “P/F 3L3-005-05 Philco DJ K9”. I do not think I will find some 40yr old documentation on it.
2011-12-12 Looked around today and yep, can not find squat on it. Probably going to have to cut it out and try to measure the pin out.
Since I had no luck finding the information on the volume control, I decided to just gut the parts of the radio I did not need and unsolder the knob form its board. That way I can use a multi-meter to map it out.
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The knob removed from the circuit board
2011-12-13 Results not good for the volume control. I put a meter on it today. Turns out that it is indeed mono. It is three separate pots. One for power, one for volume, and one for treble. I can not run stereo thru the mono volume part. I will need to go back to the drawing board.
After doing some research I found that a car amp takes between 0.2 V and 5V for a “Line in” input. My current MP3 player puts out around 0.5 to 1V. Therefore, i need to preamp the signal to get it closer to the 5V range, and to give it some signal to run thru whatever volume control I come up with. (still looking for a radio stereo knob). After HOURS of searching the net, i found this. It will amp up to 10X (2.8V). I could not find any dimensions I hope it will fit inside the radio chassis.
https://catalog.pac-audio.com/catalog/audio-interfacing/ld-10?search_query=ld-10&results=2https://catalog.pac-audio.com/catalog/audio-interfacing/ld-10?search_query=ld-10&results=2
Well Some good news!! My dad had an old FM radio that was in his motorcycle. I took out the FM volume control.
After taking the Pot out of the radio, I painted the case, the AM needle, the Plate behind the needle.. I then put the FM pot into the AM radio. I put the knobs on the AM and FM pots. It matches up very well.
Believe it or not, it works!!! Got the switch wired to the pre-amp, addes some power and wala…AM stereo MP3 player.
2011-12-21
New knobs are here and on the radio, so that makes it officially done.
Overall I am really happy with the outcome. I accomplished my goal of having an MP3 Stereo player in the Maverick without changing the look of the AM radio. There are a couple things that did not come out like I wanted. The Stereo Pot that I put in is a little high in resistance. Thus I really get no sound in the first 25% of the knob movement. I chose a bad spot to put the input on the side of the radio. Lastly, I have no fader control, or L to R, on the radio knob. There is an internal adjustment on the preAmp.However, this did allow me to use some new Cougar knobs (pictured above). The fader knobs do not exactly fit, but since mine do not work anyway, it doesn’t mater. They still look good.
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Just and update:
I finally mounted the radio in the Maverick and added a Bluetooth in the ashtray.
