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AUX input for CB?

G

Griffen

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Feb 8, 2018
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Didn't really see anything anywhere else one here, so if it's somewhere and I missed it or this is the wrong section my bad.

I have a cobra 29LTD, and I'm trying to find out if I can somehow hook a 3.5mm headphone input to it so I can play sounds out of my PA speaker. I've been looking around the web and can't seem to find anything
 

Ahh, a headphone INPUT?

Not so sure about that. Headphone is an output device.

I think what you mean is to install a 3.5mm headphone-type jack for audio input, right?

I'm not aware of a do-it-yourself setup you can copy to add an auxiliary audio input to the transmit modulation.

What kind of drive level do you want to feed into the radio? That has a big influence on how you hook it up.

73
 
my guess is that he wants a line level output from his CB radio so he can plug it into his stereo system and play the CB radio through it.

I do this with my radio, and i love it!
bypasses all the audio sections of the radio by sampling right from the volume control.

Do this, into an EQ then into the stereo and you can really pull weak voices out of the mud.

Griffen, this takes more than just mounting a jack and wiring into the radio, you have to build a circuit to convert the signal from the volume control to a line level.

Care also needs to be taken with shielding this circuit so you don't end up picking up your own transmissions.
LC
 
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Use a xformer . . .

I use a xformer out of the CB radio into the line level input of a computer so that I can run the SINAD program with a SG to align radio receivers . . .works fine . . .

Sooo - to run a CB radio into the car stereo input (if you car has one); I'd try the right xformer. Should work; don't see why not.
 
Last edited:
loosecannon said:
my guess is that he wants a line level output from his CB radio so he can plug it into his stereo system and play the CB radio through it.

I do this with my radio, and i love it!
bypasses all the audio sections of the radio by sampling right from the volume control.

Do this, into an EQ then into the stereo and you can really pull weak voices out of the mud.

Griffen, this takes more than just mounting a jack and wiring into the radio, you have to build a circuit to convert the signal from the volume control to a line level.

Care also needs to be taken with shielding this circuit so you don't end up picking up your own transmissions.
LC
Click to expand...

That works good. I used to tap the volume pot and use some good quality pc speakers or send it to the mic input of the PC for recording.

I used a 10uf non polarized cap to prevent a ground loop but a 1:1 isolation transformer would have probably been better.
 
The audio distortion level of a CB audio amp is really high. Most of them are rated close to 10%! Going to all of the trouble to sum a stereo source (since these amp are monaural) - then put it thru a weak and distorting amp - is not really the most savvy thing to chose to get that job done - IMO . . .

Seem to remember a CB that had a similar function. It is the Ranger RCI-TLM1:
http://www.cbtricks.com/radios/rci/rci_tlm1/index.htm

rci_tlm1_sm.jpg
 
Last edited:
Griffen said:
Didn't really see anything anywhere else one here, so if it's somewhere and I missed it or this is the wrong section my bad.

I have a cobra 29LTD, and I'm trying to find out if I can somehow hook a 3.5mm headphone input to it so I can play sounds out of my PA speaker. I've been looking around the web and can't seem to find anything
Click to expand...
You could isolate the PA jack by cutting traces on the PCB, not recommended because this is permanent.

PA Speaker Jack To Line Level Input
The last time I did this I used a relay (toggled by a switch on the front)
to switch the audio signal path that way you can use the mic or flip the switch and use the input jack, I had to use shielded cable and I believe It had problems at first because of lack of bypass caps and coupling issues, so I used some .01uF discs (and a 100K Ohm in series with a 47 uF to the input of the TA72222 or w/e high level audio chip is installed) I believe I also had to cut the trace leading up to pin 4 of the TA7222. I wasn't using a true line-level source, hence the 100K Ohm resistor.

When the switch was toggled "ON" the voltage from the TX/RX switching transistor initiated the relay, or you could use almost any TX switched voltage rail, it doesn't have to be right off that transistor.
When the relay is not powered up, the "stock" audio chain is used including RX audio.


It was rude and crude, but worked.
https://electronics.stackexchange.c...-reduce-an-audio-signal-to-proper-input-level

I'm sure a better way to do this would be utilizing an electronic switching scheme.. but this is the way I did it.
 

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The issue of a separate "Aux" or direct-inject audio input raises some questions.

First, should it work alongside the existing mike input? Or will this input take the place of it altogether?

If you want BOTH the mike and your added input jack to work, this raises another question. Do you need to set the gain for this "Aux" jack separately from the mike-gain control already on the radio?

If so, you need that new input jack AND a second audio-gain control for it, both.

And if all we want is a separate jack, we can feed it into the radio's mike input so that the front-panel gain control will control the Aux input level.

The issue of a transformer has to do with where your external-audio signal comes from. If it will be from a computer sound device, you risk having squeal problems unless the Aux audio is isolated from the radio's ground circuit. An audio transformer keeps the ground circuits in the radio isolated from the ground in your computer-sound device.

This is what we use.

j4Bfj4.jpg


OxCJiz.jpg


But it's not ready for prime time. No instructions or install info yet.

73
 
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