My Factory AM Radio is now mp3 Compatible!
 

To read further discussion on this topic go here- LINK


I’m the type that likes the look of a stock dash and radio but wants a modern sound system. A few weeks ago I bought a Rockford Fosgate Omnifi mp3 player. It’s basically a 20gig hard drive based system (easily upgradeable to 120gig) that allows you to transfer mp3s from your computer to your car via USB or optional wireless (which I have).

I had planned to run it stand-alone directly to my cross-over/amps, but I soon found out that it has no built in pre-amp, so no volume control. My existing 10+ year old CD player had no audio inputs either (the way the Omnifi was designed to be installed). I looked at the USA-1thru6 options, but didn’t really want a new deck.

I decided that all really needed to run this thing stand-alone was some sort of volume control capability and power antenna signal. So I did a little google’ing and found info on in-line RCA volume control. A trip to Radio Shack and I was ready to do a little radio surgery.

I picked up some 0-10k ohm potentiometers and surface-mountable RCA jacks. I later discovered that 0-10k was insufficient and went to 0-1M ohm. The 0-10k pots only adjusted volume from 100% down to about 90%. The 0-1M pots adjust volume from 100% down to about 5% (plenty low). A further improvement may be possible using this configuration. My setup works just fine, though it does get a little touchy/sensitive near full volume, meaning a little adjustment goes a long way in volume. But it's not enough to be an issue.

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When you remove the covers from the radio you can see there is plenty of room to do this. Just take out a few components behind the volume knob. I didn’t use nor did I plan to use the radio as an actual AM radio.

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The existing volume/tone knob has two pots (two are required for stereo volume control) so at first glance I thought this was going to be easier than expected. But they are not matched and are the wrong specs for the job. But the amazing thing is that the annulus (resistive disc - more info here), is nearly identical in size/shape from stock to new. A little clearancing on the new ones and they fit perfectly.

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Re: My Factory AM Radio is now mp3 Compatible!
 

Now, the other thing I learned is that the stock sweepers don’t work very well with the new annuluses. They look like they will but when I tested them in this configuration there were open spots in the volume range. So, tried gluing the new sweepers onto the stock sweeper discs. That seemed to work ok, but when I went to the 1M pots I decided to use the new sweepers AND their plastic discs. I did this because the centering of the sweeper on the annulus and shaft is critical. I just drilled holes in the center of the black plastic sweeper discs to fit them over the shafts.

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Re: My Factory AM Radio is now mp3 Compatible!
 

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Drilled holes and mounted the RCA jacks. I would move them forward or to the bottom of the deck if I had it to do over because they are pretty close to the wiper motor as is.

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Another great thing about the stock pot housing is that it has a built in switch. This was the main reason I chose to stick with the stock pot housing instead of trying to find a compatible dual-gang pot. I wired the switch up to the existing power jack in the back of the radio. So two of the spades in that jack are now used for power antenna (on/off signal to the crossover, amps, and mp3 player), and the other spade is now connected to the internal light. I later wired the radio light to the dash light circuit so it will be on/off/dim with those. You could wire it to the knob switch if you want it to switch on/off with your system, but I like the back lighting on and dimmable even when the system is off.

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Re: My Factory AM Radio is now mp3 Compatible!
 

I left the tuning mechanism alone so the kids can sill push the preset buttons and watch the needle move all day long. But you could build a balance/fader knob on that side if you wanted using the same technique and simply wiring one pot inversely as is also explained here.

I installed a new bulb while I was in there (also put all new bulbs in the rest of the dash).

This set-up would work for any audio device that is designed to be run through AUX inputs in a deck and has its own control interface.

Here it is installed. The faceplate is pretty thin and could be mounted anywhere, but it's going here for now (hot glued on so it's easily reversible).

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Next install; my new covered fiberglass kick panels thanks to this FAQ :metal:

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Re: My Factory AM Radio is now mp3 Compatible!
 

Thanks guys. The basic idea was pretty simple, but making it work the way I wanted it to using some of the factory parts took a little trial and error. Now that it's all figured out it would be cake to do again. I just wired up the radio back light today so I went outside a few minutes ago to check it out after sun down and it looks great :)

I think I'll move the Omnifi face-plate somewhere else in the future and put the ashtray back, but for now this works.

You could run a stand-alone CD changer or HD-Radio unit this way too.

Here's a link for jaros http://en.wikipedia.org/wiki/Mp3

Re: My Factory AM Radio is now mp3 Compatible!
 

You should try using audio or log tapered pots for volume controls, instead of linear. This will give you the "normal" control you expect from a volume control.

Neat setup. A lot of AA5 tube radios in the 60's had a "fader" arrangement for plugging in a phono; with nothing plugged in, the volume control worked as normal, but, with a audio sourse plugged in, and the radio tuned to an empty spot on the dial, the knob was used opposite of normal (full clockwise was min. volume). I have thought of modifiying my truck's stock radio this way so I can still use it as an AM radio. I know it wouldn't be stereo, but I could mix both channels together with two 1K resistors and get true mono from any stereo source. It wouldn't be hifi, either, but that's why I got a nice amp at home.

Anyway, nice job!!!!

Re: My Factory AM Radio is now mp3 Compatible!
 

Thanks for all the comments guys. That's what makes posting stuff like this worth while.

Oldgold, I actually looked for logarithmic pots, but found the linear(s) in the right size/shape/specs/price so I went for it. Sweet amp you've got there.

Re: My Factory AM Radio is now mp3 Compatible!
 

Update!

I decided that mounting the control panel in place of the ashtray went against the whole purpose of running my audio through the factory radio--to keep the stock look. So I ran the cable up the A-pillar (thanks to Rockford Fosgate for providing plenty of it), and over to the the spot between the visors. I will admit that it was easier for me to do this because it's a Suburban with the headliner removed. Yes I did have to drill one hole, but I also weld... Now I can get one of those cup-holder ashtray replacements :)

Here's the before and after: