Any good solutions for two radios on one external speaker?

[troyboy162]

Thank you! I played with it a bit and I'm starting to understand ltspice more. It would be nice to use a standardized program instead of multisim.

If I can ask you a question... The whole circuit banks on the fact that I can knock down the speaker outputs to line outputs. I've seen and heard a few ideas on this. One is to impedance match like you were saying. Give the HAM/CB output a dummy load in the 8 ohm range and allow it to operate business as usual. The others involve outputting into much higher impedance like a buffer amp or the 10k resister I have. I've researched on google and I think that the high impedance load will be ok since the CB/HAM cant drive any amps into something over 1k ohms. I am assuming that means no damage to the radios and I can knock down the signal to line level at the same time...and they are resister isolated from one another. Is that a safe bet or am I risking damage?

 

[DaveInDenver]

In general putting a high impedance on speaker amplifier outputs won't do any harm. I will caveat that by saying sometimes too high of an impedance can hurt an amp if you are only running the line level converter, this could start to look similar to running it open load and cause issues depending on the amplifier configuration. Probably not a problem on two-way radios with cheap and durable audio amps but high fidelity amps might not like looking into a high impedance. It's a power transfer issue and by /not/ transferring power to the speakers it rattles around in the amp, which overheat or stresses it. If you tap the converter from an output that also has a speaker, this would be less difference to either the speaker or the amp.

The high impedance front end of the converter also takes care of knocking down the level, it's a high impedance in parallel with a low impedance. So even if the speaker is running at 2W into a 8Ω load, you're talking 4V nominally, maybe it peaks at a few volts at most. Looking into a 10K input that is going to give you 400µV.

I'd do it like this, add an isolation transformer to prevent ground loops (you are turning a floating differential output into a ground-referenced single ended) and use a voltage divider to adjust. FWIW, the first stage here is an active full wave rectifier with the amplitude being that of the input peak up to the positive rail.



If you use a 1:1 xfmr that is nominally 600Ω you will drop the voltage quite a bit, I would expect you'll actually be way too low (probably tens of mV). You could do a 8:1000 matching transformer (essentially an audio amp output xfmr in reverse), this would give the audio amp a consistent load and prevent the signal level from dropping too low. With a 10K and 10K pot you'd probably be sitting around 1Vp-p, right on a line level signal.

 

[Borrego60]

Make it easy double throw double pole switch toggle switch and one speaker.

 

[Utah KJ]

If you did it my way, you'd be done by now.