Mobile audio combiner?

[Pj]

Looking for a decent inexpensive audio combiner. 4 inputs, 1 output hooked up 2 Astro Spectras and 2 Orions. Of course, its can't ground the lines to blow the audio chip.

Any suggestions? M's is like $450 and I am NOT paying that.

[jim]

Get (5) 10w 70V audio transformers. Put the each radio audio output into the 8Ohm outputs of 4 of them. Tie all 5 of the 70V inputs together. The speaker will go to the 5th transformer's 8Ohm output. Works great.

[KB5AKO]

It sounds like a combiner is equivalent to an audio mixer. Is the audio intelligible whenever all 4 inputs are active at the same time? I sure would like to hear a recording.

Victor, KB5AKO

[MSS-Dave]

Audio mixers usually run at mic or line level. Pj needs speaker level up to 10 watts (think that is what the Orion will do max...) Jim has a great idea with the 70 volt transformers, gives 8 ohm load to the radios, uses the 70 volt winding as a "bus" per se and then 1 8 ohm output for a speaker. Just make sure the speaker is rated for the 10 watts at 8 ohms...

Dave

[jim]

When multiple audios go through it, it sounds just like if you have 3 or 4 or whatever number of speakers. A true wacker can listen to all 4 at once and understand what they all said!

[Josh]

Will this same method work with two radios instead of four?

[JAYMZ]

When multiple audios go through it, it sounds just like if you have 3 or 4 or whatever number of speakers. A true wacker can listen to all 4 at once and understand what they all said!

Then PJ has nothing to worry about.

What if you have radios with mismatched audio output? Say one is 10 watts, and another is 6. Does that happen? And if so, what do you do then?

[Jim202]

Adjust the volume control to the sound level desired.

Jim

When multiple audios go through it, it sounds just like if you have 3 or 4 or whatever number of speakers. A true wacker can listen to all 4 at once and understand what they all said!

Then PJ has nothing to worry about.

What if you have radios with mismatched audio output? Say one is 10 watts, and another is 6. Does that happen? And if so, what do you do then?

[Josh]

It's funny (not) how my added comment revived this old thread on a different tangent.

[ke7joi]

here is how I would do it you very the power rating of the transformers to change the 70 volt line voltage balance. If radio 1 is only 5 watt you use a 5 watt transformer. If radio 2 is 10 watt use 10 watt transformer. Any question pm me and I will try to anwser them.

[JAYMZ]

here is how I would do it you very the power rating of the transformers to change the 70 volt line voltage balance. If radio 1 is only 5 watt you use a 5 watt transformer. If radio 2 is 10 watt use 10 watt transformer. Any question pm me and I will try to anwser them.

That's the answer I was looking for. I assumed that was the case, but wanted to confirm.

Thx!

[jackhackett]

Josh: the answer is yes.

[26M10]

http://www.fleetradioproducts.com/htm/model301b.htm

This is what I use....

The best part is that it has a master volume control so you can mute all the radios at once.

You basically unsquelch the radio and then turn the radio volume control all the way up then adjust the pot on the 301 so that the clip light just starts to come on.

Then you adjust the radio to listening volume.

Then you can use the master volume control to control all the radios at once..

They are awesome...We install them in all of our command vehicles..

[motorola_otaku]

Anyone got a Mouser or Digi-Key part # for the required transformers?

[ke7joi]

The transformers are depent on the output audio power of the radio. Most electrontic and music stores carrie them, Company that do industrial sound and intercom systems. digi-key does not carrie the that I know.

[Josh]

OK,

I went ahead and gave this a shot.

It works, sorta.... I mean, it does combine the audio, I'll give you that, but when both radios are unmuted, the overall volume level decreases and I don't know why.

I don't have the radios wired backward, I have it just as shown above. I have the transformers set at 8 ohms on one side, and 10 watts @ 70 volts on the other side, with other selections available.

I don't know if that makes a difference or not reminder, the radios I am using are Astro Spectra units. I assume they want 8 ohms and are 10 watts.

-Josh

[Al]

[It works, sorta.... I mean, it does combine the audio, I'll give you that, but when both radios are unmuted, the overall volume level decreases and I don't know why.]

The method described is a "poor man's way" of combining audio. When inactive radios are muted/unmuted the internal output impedance changes from high to relatively low. Using the transformers as described, the active radio is backfeeding the inactive radios as well as the speaker, so the external load the active radio sees is changing depending on how many of the other radios are unmuted. A much better method would be to combine at low(volume control) levels to provide isolation between all radios, then amplify the resultant combined signals to feed one speaker.
The Fleet Radio Products unit described in the link above does just exactly that but at a higher cost.

[Josh]

Oh, ok.... at this point I'm almost tempted to go back to the way it was, with multiple speakers, but we'll see if it doesn't grow on me first.

Thanks!
-Josh

[jackhackett]

Something you could try, add a load resistor on the radio side of each transformer to load it down a bit when the radio is muted. Not sure what value would work best, maybe something like 16ohms at 2watts? You'd lose a bit of volume but it might make the drop less noticable.

[Josh]

Something you could try, add a load resistor on the radio side of each transformer to load it down a bit when the radio is muted. Not sure what value would work best, maybe something like 16ohms at 2watts? You'd lose a bit of volume but it might make the drop less noticable.

I'll give that a shot when I get back home.

The speaker I'm using is a 3ohm one. I've added resistors on the speaker to make it 7.5 ohm (almost because at the low impedance, the astro spectra radio's speaker pops loudly when unmuting, this was brought up some time ago... and it's not caps, it's the VOCON.

At any rate, I can remove them and put a matched set on the radio side of things and see if it makes a difference since I've already got the volume loss already.

-Josh

[Will]

Josh,
If you are trying to use the transformers on Spectras, you are going to have problems.

The Spectra audio output IC will go into oscillation with that much inductance from the transformers. This can kill a audio IC in a Spectra or Astro Spectra.

The radio that is not receiving will not present a load, but when two radios receive, the load goes way off. A severe mismatch. The volume at the speaker will drop dramatically...

Save some money in repairs and get the audio combiner. It has an amplifier IC in it to drive the speaker, much the same as the Spectra audio IC. The combining gets done without any interaction or loading of the other radios hooked to it.