Connecting CB Radio and Pro Audio --- How it's done

[madsage]

Obviously you were able to patch into the radio mic IN, right from audio card OUT?

If it's coming from the audio card the microphone amplifier stage in the radio should be bypassed and the output of the audio card should run directly to the modulator to get the best frequency response.

Yeah, I agree. I know motormouths mauldulator install is like that.
Until I know where and how that is done. I'm using a center tapped audio transformer, half the winding on the input. The output is two legs to the mic, bypassing the power mic pre-amp board.

Reason i asked is the mic pre-amp is already balanced for proper impedance. One 'might' be able to adjust gain with the preamp drive?
I never tried this myself, but was plan B if my isolation transformer didnt work out as expected. However it worked liek a charm. And about the same exact level of input as my power mic was with the PC loudness adjusted to about 1/3rd, and mic input about the same, on my PC system. And Cobra2000 Dynamic at 9am.

The partnumber on the audio transformer is ratshack 273-1380. about 3bux.
it is a 1000:8ohm ratio and freq response of 300-10khz +/-3db, (plenty for CB)
if anybody is interested. Isolation is a must in most cases, And impedance match required.
This should get you close.

933Arizona




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[Night Crawler]

The transformer would be used since it's stepping up the impedance and will add isolation then couple the audio with a resistor and capacitor to the modulator instead of the microphone input.
As example here is a block diagram of a 949
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Every radios connection point will be a little different but the concept is the same. The audio would be coupled on the 949 through a resistor and capacitor at the intersecting point between IC6 the SSB Balanced Modulator and Q53-Q55 the AM modulator after the Mic Amp IC7.

[madsage]

The transformer would be used since it's stepping up the impedance and will add isolation then couple the audio with a resistor and capacitor to the modulator instead of the microphone input.
As example here is a block diagram of a 949
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Every radios connection point will be a little different but the concept is the same. The audio would be coupled on the 949 through a resistor and capacitor at the intersecting point between IC6 the SSB Balanced Modulator and Q53-Q55 the AM modulator after the Mic Amp IC7.

Cool thanks, I will do some experimenting on a 148, and see if i can find a better input point.

933Arizona

[Radio1cb]

hey you guys would fit in perfectly at my station

[Radio1cb]

hmm come to think of it this would be an outstanding topic for a new call in radio show i want to devolop. perhaps some of you might consider coming aboard? its 5 am right now and ive been reading your posts and i must say im riveted by the excelent points made and ideas shared. im glad i decided to re-join this forum.

[Slim Pickins]

How about hooking a set-up like this to a tube final type radio. I was thinking about trying this with my FT101E but not sure about the impedance difference. Like mentioned earlier most modern mixers are 600 ohm output and the FT is much higher. How would I compemnsate for that difference?

[Night Crawler]

The 101e is not using a tube speech amplifier but a FET (field effect transistor) for the first microphone amplifier stage but never the less that would still make it high impedance.

What you could do is try connecting the output of the mixer to the mic input or phone patch input and see how it works it might not require anything since the mixer usually has a buffer amplifier after the mixer stage which might have enough gain to compensate for the mismatch.

If that doesn't work out what can be done is to use a low to high impedance audio matching tranformer or another option would be is to use a transistor amplifier stage between the mixer and the mic input of the rig.

[Slim Pickins]

The transistor amplifier stage you mention is like a mic pre-amp?

[Night Crawler]

It's a very simple general purpose preamplifier circuit delete R1 the 10k resistor and electret condensor mic and change C1 and C2 the coupling capacitors to a 4.7uf or 10uf non polarized for better frequency response.

The output of the mixer will go to C1 and the output of C2 will go to the rig a pot could be added from C2 going to the rig and used as a gain control if you like.
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[Slim Pickins]

Ok, I will give it a try. Looks like a pretty easy circuit to build.

Thanks
Paul

[Rooster173]

Honestly this is my view on hifi systems after researching a bit, if you want to sound like youre speaking on an fm station sure these will work but honestly with the right super mod and tech working on your radio you can get amazing audio without using all of the equalizers and mixers. Ill take my rci2995 and echomax 2000 anyday. I have even been asked a few times if I was operating a hifi station. Now dont get me wrong I'm not knocking these stations at all I just believe for the investment theyre not worth it thats all

[yamaha]

I did it to a galaxy sirius. Input audio into board after all filters and preamps. i run the sirius with a sony crystal mic and a TEAC preamp and eq. They cant get your full range audio unless their receive has opend up a little. Im no MMM but it will carry you out better and allot cleaner. A clean 5 watts is better then a wacky 500 on the ear and s units dont mean a thing without the swing to go with it.

[0498]

I like all the info i am seeing but one question i can't find so far is the connection point in a Uniden ebay.us/5Zgwnh" class="postlink autolinks">PC76xl is it the same as a Cobra 29 if so i have not been able to find it so far if it is a different cap let me know i have been gathering up needed supplies and programming to do this but need to know this connection location not wanting to go through mic amps in radio prefer to direct inject!