Greetings.

As above.

There are very few stations available on AM anymore, and most of those don't broadcast anything I want to hear.
While I know that there are a few RF (plug-in-to-the-antenna) auxiliary adapters for AM radios, that just seems so... kludgy.
Therefore, I plan to make my own 1/8" (3.5mm) Aux. input, so I can plug in a tiny Bluetooth adapter, and listen to what I want to hear on the radio.

This is a 100%-original car, so I don't want to hack it up to install a stereo, like I did with every other car I ever owned.
I just want to be able to listen to the radio, like we did back in the day.

I realize that I would probably get more responses over on FABO, but most of those would be telling me to turn the trunk into a subwoofer and power it with a portable generator, and drop in a 340 while I was at it, so I figured I would see whether there were any electrical engineers here who could comment intelligently.

I came across a plan from a gentleman named Nali, posted on the AMC forum in 2011, which seems to make sense, but I wanted some clarification, and there's no response to my question over there (surprise).

I redrew his schematic, and have posted it here:
Basically, you break the line-level output from the tuner stage to the volume control and instal a DPST switch (or a switched 1/8" jack), the two 220Ω resistors allow you to combine the Left and Right channels without harming the Bluetooth unit's line-level amp, and two 33µF and one 68µF caps filter DC.
The "ground" level of the AM Radio's audio amp is definitely not the same as the chassis / vehicle ground (I have the Sam's sheet for the radio), so that needs to be isolated, as the standard available Bluetooth units carry their grounds from the USB power plug through to the common of the 1/8" stereo connector.

I am not sure whether he intended the "Unknown Value" resistor to be one that I would use, or to be representative of the resistance already in the system after the volume pot.

My actual plan is to make a very small sheet metal panel, maybe 3/4" tall, to screw to the bottom of the dashboard using the fuse block and radio bracket screws, containing two USB-A receptacles and two USB-C receptacles, plus a 1/8" stereo Aux jack and a DPDT "micro-mini" toggle switch I have, to provide for charging, Aux input, and switching between the Aux input and the AM radio. I have a very nice little Bluetooth receiver that plugs into a USB-A for power and has a 1/8" plug on the other end for output that I could then plug into the panel.

My questions are:
• Do the values of the resistors and the caps look okay?
• Does this look like it will adequately isolate the radio's components from the vehicle ground?
• Does anything else look wrong / Does this look like it will work, without releasing the difficult-to-replace OEM factory smoke?
• Any other suggestions (other than the 340 or the subwoofer)?

Thank you in advance,

– Eric

You can save yourself a lot of time and headache by just ordering a pre made Bluetooth amplifier board that has a built in aux and USB port. I just did this conversion two weeks ago on my ebody AM radio. It looks factory from the outside but the volume knob works to control sound and pause and fast forward while supporting both Bluetooth and USB drives. I went with the mono version because I have a single speaker dash, but they have two channel and 2.1 channel ones available for pretty cheap.

200W Bluetooth 5.0 Amplifier Board TPA3116D2 100W+100W Stereo Dual Channel Amp Board Audio Receiver for Home DIY Speakers https://a.co/d/flnUOZ8

https://www.forabodiesonly.com/mopar/th ... 1974875032

_________________
1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue

Very interesting.

And very nice work.

This is just the sort of information I need to consider, before I make any moves.
The 100W per channel BT unit you linked to on Amazon certainly seems more than adequate for my one 6x9 paper speaker.
(Yes, I saw that at 12V into 8Ω, it's only 25WpC, and yes, I'm going to dig out a "fancy" 6x9 from my "stereo" boxes when I get a cahnce).

I've been leaning toward adding an input to the original radio mostly because I want to be able to turn on the AM radio sometimes, but also because I just like the idea of using the original circuitry (after I fixed it by replacing the two combo electrolytic cans), but I suppose I could also just install one of these units, outside the radio case, along with a relay to switch radio power and speaker input at the same time. The BT volume control is really superfluous, as you can just adjust volume from your phone.

There was also a guy somewhere on eBay (if I recall), who was selling replacement kick panels with a bulge for a speaker. If I were using the separate unit, I could always install a pair of those, as I wouldn't have to cut anything up to do it.

I'll shovel all of this into the ol' thinker, and see what I come up with.

Thank you very much for posting this. Now I'll go read through that FABO thread.

– Eric