What CC knows about stock Jeep radios

[NickyV]

I will be paying attention!

[ghetdjc320]

Just ordered up an RX-173 that seemed to be in good shape from eBay. will be tearing that one apart as well. There is one glaringly obvious solution that occurred to me for the am/fm radio bleed through when adding an aux input, a switched 3.5mm socket. It's a super simple device that passes through signal on normally closed contacts when there is no plug inserted in the jack and automatically switches inputs when plugging in a jack. Instead of using those two pin connection on the pre-amp board, why not just intercept the am-fm radio signal to the board? 

 

I do like bluetooth options as well but unfortunately apple still does not support any real HD bluetooth options such as Aptx HD. Therefore the best solutions tends to be a USB C DAC. Installing the DAC close to the head unit 3.5mm port would shorten the signal path. The connection would be USB to the DAC then switch to analog and go to the RX series radio pre-amp board where the am/fm radio would normally plug in. It's just a 3 pin JST connection for the stereo signal. If done properly with quality components, that would be the best audio signal one could get to the stock RX series internals. The DAC analog output may have to be attenuated down to the appropriate line level voltage to match the am/fm radio levels when switching.

 

On the output side, a nice DSP would work great to not just make up for the stock amplifier limitations, but also to tune the cab acoustics. I'll post up how this works out. I think the current RX-172 I have I'll just gut entirely for a future raspberry pi setup with an OLED screen but the RX-173 I'll use to optimize a factory component system. 

[fiatslug87]

That sounds like the Scosche IPFMRDS I have in my three MJs. Made for iPods but a lightning adapter lets me use my iPhone.

 

 

[ghetdjc320]

5 minutes ago, fiatslug87 said:

That sounds like the Scosche IPFMRDS I have in my three MJs. Made for iPods but a lightning adapter lets me use my iPhone.

 

 

Ive used those in the past. But those still use the FM radio tuner to carry the signal. I'm wanting to run the DAC signal direct to the pre-amp board and disconnect the tuner output altogether. 

[ghetdjc320]

I was staring at the disassembled radio for a bit… Really wish I had the diagram or schematic for the RX series of radios. However, I’m wondering if, when the cassette is inserted into the deck it mutes or shuts down the radio tuner entirely, thus preventing the bleed through. I wonder if there is a way to emulate the tape being present when an aux input is applied. I’d assume there is some simple 12v or 5v logic commands that trigger the display to show tape commands. And since there isn’t really any input change command, I’m assuming this is just a logic curt unit that mutes the tuner or puts it in standby. I’ll either have to dig up a schematic somewhere or just get the multimeter out and test away.  
 

In a nutshell, here is what I’d like to accomplish on a mostly stock radio:

1. Eliminate the tuner bleed through without disabling the radio or attenuating the gain. For this I’m thinking simply intercepting the radio input to the preamp board in some fashion. A switched input jack would do the trick nicely. But an automatic method would also be nice. 
 

2. Get the display to show different information other than radio station while playing aux input. Emulating tape deck display functions seems like the go to option here. 
 

3. Get the stock play, rr and ff buttons to control the aux source. This one is a bit tougher with stock components. 
 

 

[ghetdjc320]

Did a bit of signal tracing on the preamp board. Also desoldered the mounting plate for the volume and tone pots. I hadn’t noticed before that there are several adjustable potentiometers on the board. Two of them attenuate the tape deck input. How I would love a good diagram of the board lol

 

 

[NickyV]

14 hours ago, ghetdjc320 said:

How I would love a good diagram of the board lol

Check your DMs!

[ghetdjc320]

4 hours ago, NickyV said:

Check your DMs!

Awesome! That was the missing link. So it looks to me like those pins everyone uses for aux are just test points on the PCB. My current goal is to intercept the am/fm signal pre tone controls, and add a switching input that will pass through am/fm but switch to aux or Bluetooth when signal is present. I want to have this trick the radio into thinking a tape is playing so the radio station display goes away. Then have the play, rw and ff buttons trigger a DSP to skip songs and play/pause. That logic looks simple enough. I’ll add a transistor to transfer that logic to the DSP to trigger this functions. I’m liking the tinysine DSP boards with Bluetooth. I can have a clean aux input for my DAC and a Bluetooth for regular wireless pairing 

[ghetdjc320]

As I’ve been compiling data and studying these radios in some detail, I need to jot down some of the info I’ve found so far. Some of this is my operating theory and I’ll update it with further confirmation. To preface, I have both an RX-172 and RX-173 in hand and a schematic from an earlier RX. Here are some of my findings:

 

1. TP pins such as TP371 and 471 are “test points”. There are many test points on the board, likely to validate the circuits upon or before assembly. 
 

2. TP371 and 471 seem to just sit on the line level input to the tone controls (starting with treble). They are not specifically the tape or tuner signals but rather  combined signal. 
 

3. I do not see that there is necessarily any discreet “input selection” in these units. Currently, I’m thinking it is the presence of the tape that sends a “mute” signal to the radio. Some have reported long ago here in CC that removing the tape deck, inserting a blank tape or disabling the am radio will eliminate the audio bleed through issue. There seems to be some logic here but I’ll have to do some testing to confirm. 
 

4. The preamp is labeled as PCB-VR on the drawings. It looks like there have been a few variations of this over the years but the final output to the amplifier portion of the board is the 3 pin connector with red white and black wires. On my RX-172 that is P304 on the pre-amp board (the one with the tone and volume controls). You should see a cable coming from there going to the main board input P304 near the amplification stage. NOTE: this is where one should be able to get line level aka RCA pre-out signals for an external amp. This is before any amplification takes place. The amplifier in these radios seems to just be a simple 2 channel design, which is further substantiated by the lack of a fader control (front and back biasing) and only a balance control (left and right biasing).

 

5. The AM tuner is the longer vertically mounted pcb that is against the left side of the radio viewed from the top. 
 

6. the FM tuner is smaller but parallel to the AM tuner and also sits near the left side for eh radio as viewed from the top. 
 

7. The amplifier itself sits on the main PCB board near the antenna input. It is not the vertical board mounted behind the main radio harness connector. 
 

8. The AM/FM radio inputs appear to be coming from the 7 pin connector from the main board near the FM tuner to the pre-amp board. The tape input is separate and comes into the preamp board on a 3 pin ribbon wire. 
 

9. There are adjustable potentiometers all over this board. I’ve heard the rumor about “lowering the AM radio volume” as a work around for the signal bleed through issue. I can see how that could be accomplished. I’ll have to determine which pot that is, but a simple adjustment with a small flat head screwdriver would take care of it. 
Edit: I think it’s pot 71. You can see it circled in the picture just below the volume and tone controls. Turning it counterclockwise should lower the output. 

 

More to come as I delve deeper into these head units. 

[fiatslug87]

They do have fade, front/rear. Can you also pdf the wiring diagrams and add them to this post? Thanks

[ghetdjc320]

1 hour ago, fiatslug87 said:

They do have fade, front/rear. Can you also pdf the wiring diagrams and add them to this post? Thanks

Interesting, I’m only finding a balance pot on the RX-172 I’m working with. Since the diagram I have is from another member, I’ll leave it to his discretion to post. There are many aspects that are the same as the later models but many that aren’t. The manual I have is of an RX-170. I’ve been trying to dig up the manual for the later 172 or 173 but haven’t found any yet. If I am able to get one, I’ll post up whatever I can. If anyone else has one, please let me know. The signal traces from the AM/FM tuners to the PCB-VF are quite different on the 172/173 than on the 170.

[ghetdjc320]

Just to confirm, the 3 wire jacketed cable running from the preamp to the back of the board is indeed the line level audio output to the amp stage. This line is volume attenuated and tone adjusted already. A couple of good workable solutions for a clean aux/bluetooth input would be to interrupt the TP371 and TP471 tracers on the board and feed them through  a switched input device, or run the preamp output to a DSP with external pots controll. So basically, if you’d like to have RCA pre-outs for an amp, there are a couple of viable options here. The stock amplifier seems like a decent quality unit, but I have not yet determined the frequency response. More to come. 
 

I will say, the stock RX-171-173 have some interesting differences but seem very well made. 

[ghetdjc320]

So I’m reading .15 vac or .21vrms on the preamp audio output. To get this reading I applied a 60hz sine wave input at max volume with tone controls at neutral. This is quite low to run directly into RCA outputs. Given the internal build quality and lack of DSP in this radio, I think the best signal path for amplification will come from the speaker level outputs. I’d be inclined to run a 4 input line output converter to preserve the fader function (in my case I’d use them as a subwoofer bias for my b pillar subs project). I believe someone else noted the outputs as being around .6vrms. Not sure where that reading was taken and with what method. 

[A-man930]

I appreciate your dedication! 

[ghetdjc320]

16 hours ago, A-man930 said:

I appreciate your dedication! 

Of course! Happy to help demystify these things a bit. 

[ghetdjc320]

Further testing has revealed something interesting that is my current working theory. While tracing signal flows, you can find the distinct AM, FM and Tape sources all coming to the pre-amp board. They first go through the tone control stages starting with treble, then bass, then volume, then out of the board on that 3 pin jacketed cable to the amp stage. Interestingly though, the balance and fader controls have a separate 6 pin connection that seem to run their logic at the amp stage. So basically, if you want to retain fader and balance controls without heavily modifying the PCB, you'll need to use the speaker level outs. 

 

Interestingly enough, when I adjusted the AM gain pot on the main board, I got zero am radio bleed through while using the aux in. Removing (or just disconnecting) the tape deck main plug also accomplishes the same thing. It appears that the AM/FM signal is always present at the preamp stage. But the tape deck logic has a radio mute function when playing a tape, causing the preamp to pickup that signal instead. When we inject audio on those test point pins, we seem to be simply overlaying the radio signal. Quite possible we are tricking a transistor somewhere on the pcb since grounding either of these pins also cuts the signal instantly.

 

Instead of using those test point pins, I'd prefer to desolder them and keep mire wiring shielded as far as possible until it makes it to the board. That should help cut down on a bit of interference I've noticed. The signal to noise ratio seems to be decent but I'm limited in how I can test this. I will say though that I am getting very good audio quality by making some adjustments to the board. And I'm very picky when it comes to audio quality  

[ghetdjc320]

Before I forget, I've been meaning to cross reference this post and link it here. This is the earliest info I came across on modifying these radios. The post is from 2010 and is from a user I am unfamiliar with though I'm sure many of you you him. Here is the link: 

 

[ghetdjc320]

Dumping some pics here of what I decided to do. My entire goal was to eliminate noise and interference, providing the cleanest audio possible. I also equalized to gain for the sources across all the inputs (AM/FM/AUX). Pleased to report impeccable signal integrity and zero noise. I’ll post up some more technical info at some point but I’m deep into building out the ultimate MJ stealth audio system at the moment. Keep an eye on my “Tomahawk” thread in epic tech for updates. 
 

In a nutshell, I desoldered unused wiring on the preamp to avoid any interference being picked up. I also removed the TP pins and wired shielded cable straight to the board. Instead of using the chasis ground, I used the dedicated signal ground shared by the tuner and tape deck. I rerouted line level cables, attenuated the tuners for level matching, and added some cable management. Also straightened the transistor and capacitor caps. Cleaned the board and conditioned the connection ports, volume and tone controls. Cleaned up the front face and ceramic coated it.

Also worth noting that I eliminated the tape player all together. I don’t use it and now the radio has much more internal airspace to route cabling and stay cooler. The old 13pin connector has been folded back and zip tied off for now. 

 

[Torq_Shep]

3 hours ago, ghetdjc320 said:

Dumping some pics here of what I decided to do. My entire goal was to eliminate noise and interference, providing the cleanest audio possible. I also equalized to gain for the sources across all the inputs (AM/FM/AUX). Pleased to report impeccable signal integrity and zero noise. I’ll post up some more technical info at some point but I’m deep into building out the ultimate MJ stealth audio system at the moment. Keep an eye on my “Tomahawk” thread in epic tech for updates. 

This is awesome. I am getting ready to do this on mine with a stealth setup. Mind sharing what set of shielded cabling you used? 

[ghetdjc320]

On 7/31/2026 at 11:17 PM, Torq_Shep said:

This is awesome. I am getting ready to do this on mine with a stealth setup. Mind sharing what set of shielded cabling you used? 

Of course, it’s a Tensily 10-06000. The shielding dumps to ground and you can panel mount it if you get a longer version. I just wanted the short pigtail though to add an aux cable to. 

[ghetdjc320]

Wanted to provide a quick update. I tested the aux input today and it works perfectly with zero perceptible interference or noise. However, if I pause the music and turn up the volume all the way, I am still able to make out radio signals. I don’t think anyone would ever know but that’s just unacceptable to me. So I still have to rid this radio of that interference. Will trace those lines and see what can be done. Now that I’ve eliminated the tape deck, I may just eliminate the tuners as well. It would just leave me with an empty shell of a radio but It would be a pure source for the system. It would be easy to add Bluetooth as well and I may still retain that as an option. It is handy to have a radio still but the audio tap method does not duck it far enough for my liking. I need that signal cut, not just hiding in the background somewhere. 

[ghetdjc320]

This is the stock am/fm radio line input from the main board to the preamp board. Now we know the audio path which looks to be the same across the RX series of radios. You can entirely disconnect this 7 pin connection which runs from the main board to the preamp but you will loose your tone controls and a bit of gain. There was no perceptible background noise difference either way so I left it connected to maintain tone controls but de-pinned the am/fm tuner. This head unit will be just a pure source unit with nothing but a clean aux signal. I’ll term this more of a “hifi” unit. But I have another RX-173 I’ll convert to a multi purpose unit and may even retain the tape player as I can see now how to cleanly integrated aux and eliminate any bleed through without disabling the tuner section. 
 

Most of the information o have seen referenced only indicates that the AM radio bleeds through. I can see why that is the assumption as the am radio gain is fairly high. But once you reduce that gain and unify it to the fm gain, you’ll notice that there is still tune bleed in both am and fm bands. To test this, connect your aux source, pause the music, and turn your radio volume to max. Likely you will hear the bleed through. 

I’ll try to identify which of these pins does what but for now, this is a simple way to defeat the tuner bleed and remove the signal from the path altogether. 

[ghetdjc320]

Just to confirm, those two end cables in that connector above are indeed the tuner L/R for the AM & FM. When viewing the white 7 pin connector as in the picture above, starting at the left side, pin 1 is Left channel pin 2 is Right channel. This is on an RX173 radio but looking at the older RX I have here, I believe this pinout logic is the same. 

[ghetdjc320]

So I’m going to build out a 2nd version of this radio. Here is the plan: I’ll install a Qualcomm Bluetooth board and an Analog Devices ADAU1701 chip. This radio will have AM/FM tuner, AptX 5.1 Bluetooth and a full DSP. I will tune this DSP for the Comanche cab acoustics in my Tomahawk. 
I’ll program the DSP to auto switch over to Bluetooth when active and switch back over to radio when not in use. This way I can default back and retain radio functions while absolutely 100% eliminating any radio bleed-through. If I get really ambitious, I’ll configure the “play” button to control the play/pause on the Bluetooth chip since the tape player will be gone. On another note, I have a couple of probably good tape players if anyone wants one. 
I do want to come up with a better solution for the button feel as well. There is a decent bit of slack. Adding felt to the buttons themselves would indeed make them stand out better but would still leave a decent gap to the actual contact pad on the front panel board. If I find what I’m looking for, it should quiet down the key presses and bring the buttons forward a bit for a better feel.