[Jerry In Maine]

In my "Ham Shack" I have two transceivers. I'd like to combine the outputs into one 8 ohm speaker. Spec sheets say that one radio's output is 4-16 ohms. and the other is 8 ohms. I'd like to combine the two into one central speaker. I'm concerned that just "tying them together" could harm the output circuitry of one or both radios. If the outputs were line-level I'd just use a cheap two input mixer, but Any ideas as to safely do this with some actual power?

 

[AnalogKid]

Go with a cheap two-input mixer and turn down the inputs. Of course, you'll need an amplifier for the output to drive the single speaker.

The nice thing about a cheap mixer is that the input level controls probably are immediately after the input connectors, rather than after some input preamp/tone/whatever circuits that might overload.

Note that unless both input sources are output transformers in the transceiver, they must share a common GND at their outputs.

An alternative is to "build out" the two sources with resistors. Again assuming there is a common GND for the two outputs, connect that GND to the speaker and both transceivers. Then connect each transceiver "hot" output connection to the speaker through a 10 to 20 ohm resistor. This will limit the cross-conduction currents to a safe value.

ak

 

[crutschow]

You could also use a dual voice coil speaker, although they tend to be a little expensive.

 

[Externet]

Complications, complications... Choose your preferred size...





Or superglue a couple of your choice, visible or wrapped/behind fabric. :

 

[Jerry In Maine]

Complications, complications... Choose your preferred size...


View attachment 70300


Or superglue a couple of your choice, visible or wrapped/behind fabric. :
View attachment 70302

I realize I could use two speakers. The speaker I want to use is in a Icom accessory cabinet that matchws the tranceiver,

 

[crutschow]

Does either of the tranceivers have an output indicating that they are on?
If so, you might be able to use that to operate a relay that selects which audio output goes to the speaker.
Or do you operate both tranceivers at the same time?

 

[Jerry In Maine]

I'd like to monitor both at the same time. Repairs on these transceivers is expensive even w/o shipping to the shop, so I'm really concerned about not putting either at risk. Looks like the safest way so far is to use a two-input mixer and final amp which was initially suggested.

 

[crutschow]

I'd like to monitor both at the same time.

So how will you now which is generating the sound when both are on?
Is there a visual indication?

 

[Jerry In Maine]

S meter on both. also, each is often receiving on different bands and operating in different modes.

 

[crutschow]

use a two-input mixer and final amp which was initially suggested.

Just make sure the two transceiver speaker grounds have no significant potential between them when both are on.
The resistor isolation would also work if the above is true.

If not, than you would need some type of differential circuit (such as an audio transformer) to isolate the two signals.

Edit: Another option for direct isolation of the speakers if the grounds aren't at the same potential, is to to use resistors plus series capacitors for both signal and ground at one of the outputs.