6 Radios to One Speaker?

[Robert Reed]

National and others make low power amp chips (0.5 t0 1 watt) output. Bring your out puts in from each radio with mixer styled input to one of these power op-amps, and drive the speaker directly from its out put.This requires no transformers at all which BTW can get expensive. If need be, each radios input resistor can be picked for uniform audio levels ( if that is a problem). O.5 to 1.0 watts into a high efficiency speaker ( usually what the cheaper ones are) can produce a lot of volume and should suffice. Only down side is you will have to supply a source of power to the Op-Amp unless this is automotive in which case it is already there. Simple - cheap - effective ! just the way I like to design . If need be I can supply some of the chip numbers I have used in the past.

[Chris Smith]

I must be doing something wrong?

With the wrong type of diode and a very weak signal, the sound comes through half wave.

Im sure it doesn’t work with all systems, especially weak signals, grounded signals and all sort of others.

[positronicle]

--Edited by Positronicle--

[haklesup]

What would be the right type of diode? One with higher or lower Vt, more or less wattage, faster or slower recovery time, Si, Ge Shottky? No matter what, you are going to have severly distorted Audio and you will still have additive power signals which can overload a speaker

The Powered Amp with its high impedance input greatly simplifies the problem. It allows you to use a passive resistor summing circuit as Extranet suggested. 10K is a good guess and ideally would match the impedance of the amplifiers input.

Passively summing the outputs to apply to a low impedance load like a speaker is going to suffer when more than one radio outputs a sound (static for example) and the two signals sum at the speaker and it sees more voltage than it should.

With an amplifier input, you generally just get clipping and distortion as long as the series resistance is high enough to prevent overstress (and 10K is) but with a speaker, you could get a burnout

look up "op amp inverting summing amp" for more ideas. It can be made from almost any op amp and a few resistors.

[positronicle]

--Edited by Positronicle--

[Chris Smith]

You almost sound educated from all that experience.

That or the usual guess work your famous for.

What summing, cant wait to hear and watch you lable all of the sums.

[positronicle]

--Edited by Positronicle--

[Chris Smith]

Probably not.

Your guessing your values here with out knowing any of the factors, components, or extra parts.

Considering that no extra stipulations have been included in my post, any one of a dozen values returned by you can only be speculative.

[positronicle]

--Edited by Positronicle--

[Chris Smith]

Its obvious you don’t.

Leave it at that.

[dyarker]

I might could do a schematic next week end if you want (and someone else doesn't do it first). Cheers,

A schematic would be fantastic, and much appreciated.
For what it's worth, if it simplifies things at all, I do have an amplified Motorola speaker I could use. It has a built in 12w amp and runs off 12vdc.

What is input impedance and input signal level of amplified speaker?

[Chris Smith]

With a 75 volt signal, the secondary MAY send a signal that is 100% recognizable even with a full wave reciter system on the secondary windings, simply because the third and forth stages will convert the half wave DC signal back into AC, like the speaker wants.

[Externet]

Hello Dale.
Those specifications are whatever the manufacturer wants them to be.
Modern units with FET IC in the input can go as high as 100K; the typical input level should wander around 1V RMS to deliver its full output.

What's wrong Chris; you are getting closer to pulling rice coins ? Come on, you just invented a new style of DC to AC inverter ! Please, Chris.
Miguel

[dyarker]

Externet,

He said he had a Motorola amplified speaker already. So it could be a VHF base station external speaker with 1V line input, or a remote with a 600 Ohm -6dB input, or something else. Big difference! I was asking about the specific unit he has.

[Stevereno]

Externet,

He said he had a Motorola amplified speaker already. So it could be a VHF base station external speaker with 1V line input, or a remote with a 600 Ohm -6dB input, or something else. Big difference! I was asking about the specific unit he has.

The Motorola amplified speaker I have is model number NSN6054A. It was intended to be used in vehicle application. I can't find much info on it other than it having a 12w amplifier and running on 12vdc.