Two Radios into One Speaker

[cellphone]

Hi All,

I have two separate radios (Kenwood TK-730 and TK-830) that I would like to connect to one external speaker. I am hesitant to simply connect both radios to the same speaker without some type of combining circuitry so I do not damage the audio amplifies on either radio. I do not want to use a switch, as I would like to simultaneously hear audio from both radios from one speaker. Also, this will I have space limitations, so a large mixer is not an option. I have searched the forums, and found options from about $150 to $400 to accomplish this. Considering that I only have about $150 invested in the two radios, I am looking for something considerably cheaper than these options.

What is the best way to connect two radios to one speaker and does not break the bank?

Thanks,

Joe

[kc2rgw]

A passive combiner is the right way if they will both potentially be on

You don't want two powered sources combined into one load.

One powered source into two passive loads is o.k., but not the other way around. You need some isolation.

It's just two 10k resistors, very basic.

Here's a great page explaining why and how.

Simple mixer

[N_Jay]

10k resisters to a speaker?

I would recommend an amplified speaker or a small PA amplifier.

Then you can use two inputs or build a isolation network with resistors.

[K8PBX]

See post #17 at this link: 2 Radios to 1 Speaker

[gewecke]

Why not a separate speaker for each radio? Simpler would be better wouldn't it?
N9ZAS

[n8emr]

Originally Posted by K8PBX

See post #17 at this link: 2 Radios to 1 Speaker

The transformer method referenced in the link is the best way outside some of the more costly electronic options. It can support many radio's to one speaker by just adding transformers.

[N_Jay]

For those that don't know, the transformer method still applies the audio signal to the output of each radio. This probably will do no harm, but if the output is configured in such a way that it tries to sink the power there could be some issues.

[rfradioconsult]

Search for dual voice coil speakers there is such an animal, hook one radio to one coil the other to the second coil, no matching, transformers, mixers needed; simple.

[kc2rgw]

Originally Posted by N_Jay

10k resisters to a speaker?

I would recommend an amplified speaker or a small PA amplifier.

Then you can use two inputs or build a isolation network with resistors.

It works perfectly....did you read the link?

Transformers can be used, but they will soak even more power. They do have the added benefit of further isolation though. Can be useful for knocking out ground loops.

[MPSCS]

2 into 1 is not a good solution if it can be avoided, it should. Any time you supply two different sets of audio into one speaker you will have a certain level of distortion. It can't be avoided regardless of the method use. You'd do better to buy two smaller speakers and glue them side-by-side, or one on top of the other, if space is a concern.

[N_Jay]

Originally Posted by kc2rgw

It works perfectly....did you read the link?

Transformers can be used, but they will soak even more power. They do have the added benefit of further isolation though. Can be useful for knocking out ground loops.

1) His splitter is for the INPUT to an amplifier, not for speakers.

2) How do you figure the transformers "soak up" more power?

Yes, transformers are helpful for DC and ground isolation. (DC isolation is most of what they are doing in this application.

EDIT:
Try on of the amplifiers here.
http://www.parts-express.com/wizards...TOKEN=36047578

[cellphone]

Hi All,

Awesome suggestions! I’m going to give the 70v transformer method a try. Frys has them for $5. I’m going to round up three of these and put them in a small electronics project box. I will let you know how this works. The audio output of the 730s and 830s is too loud the way it is. Any added attenuation would be just fine. I’m sure the audio will eventually get distorted, but if this method works, I may try adding some additional radios to the mix.

If this does not work, I will probably settle for two speakers.

Thanks again!

--Joe

[cellphone]

Hi Everyone,

I want to thank everyone for the suggestions! I picked up all the parts on Sunday from Fry’s Electronics and put together the audio combiner using 70v transformers. The end result is MUCH better than I expected!

Here is a summary of what I put together.

-Input 1 Audio from TK-730 into 8ohm side of transformer #1.
-Input 2 Audio from TK-830 into 8ohm side of transformer #2.
-Output to Kenwood KES-4 speaker from 8 ohm side of transformer #3.
-70v side of all three transformers tied together.

Here are the transformers I used:

FRYS.com*|*MT2570

I mounted it all in a plastic project box also purchased from Frys. To make the audio inputs nice and neat on the box, I mounted 3.5 mm phono jacks for the inputs and output on the box. I have room in the box for one more transformer to make for a 3 input setup. I may try a third input in the future. With all my parts (three transformers, project box, and three phono jacks) it was just a little less than $30. It took about an hour of my time to superglue the transformers down, and solder all the connections.

Audio to the speaker is slightly quieter versus one radio to the speaker. I would say the volume from each radio is about 10-20% quieter. In my situation, this is not a problem as the audio from the TK’s are crazy loud.

There is no noticeable distortion running audio from two radios into one speaker. I am picky about audio quality, but I am not able to hear any distortion at my normal listening volume. I will try at different volumes over the next couple of days and let you know if there is anything noticeable.

My only complaint right now is that the transformers are a larger and heavier than I would like. In my situation, the box can be remotely hidden leaving only the radios and one speaker in sight so it is not that big of an issue.

Overall, I am VERY pleased with this solution, and I am very grateful for pointing me in the right direction. If you are looking for a way to connect two (or more) radios to one speaker, and are proficient with a soldering iron, I would definitely say to try this. It was easy to build, and much cheaper than other options I have seen. Thanks again for the great suggestion!

Best Regards,

Joe