6 Radios to One Speaker?

Stevereno · Post by **Stevereno** » Sun Jun 24, 2007 8:02 pm

I want to have 6 radios connected to one speaker and I'm thinking of doing it as indicated in the diagram below.
Will this work OK?
Any downside or technical issues I should be concerned about?
(please excuse the elementary diagram)

Chris Smith · Post by **Chris Smith** » Sun Jun 24, 2007 8:44 pm

Your impedance will be out.

I donâ€™t know what is acceptable for your unit.

A simple diode on each secondary may fix this.

Robert Reed · Post by **Robert Reed** » Sun Jun 24, 2007 9:07 pm

I think if each of the driving transformers had the exact same signal and level on its output, this would work.However this would never be the case as probably only one scanners output would be present at any given time. In that case the idle secondarys would probably act as loads to the active one. this could be pretty hefty. Of course the radios out put circuitry would have a lot to do with your scheme.
" DIODES IN THE OUTPUT ????"

Chris Smith · Post by **Chris Smith** » Sun Jun 24, 2007 9:58 pm

Often half a signal works just fine.

Bob Scott · Post by **Bob Scott** » Mon Jun 25, 2007 12:48 am

I Like Chris's "Darkside of the Moon" album cover avatar.

But rectifying audio with a diode? Chris, did you have a brain fart for a second and think that the diode will direct the sound outwards because the arrow points that way? (My brother did once a long time ago.)

With the original diagram: One radio makes a sound, the transformers will feed the voltage back to the other radios. The amplifiers in the other radios will not like it, and will actively short circuit the signal, due to the constant voltage nature of the output amplifiers. Expect radio amplifier failures.

Bob

Externet · Post by **Externet** » Mon Jun 25, 2007 8:26 am

All the radios audio outputs have to be connected to a plain higher impedance mixer circuitry and the mix/sum result amplified again for the single speaker.
Yes, i choked too with the diodes suggestion

Miguel

Chris Smith · Post by **Chris Smith** » Mon Jun 25, 2007 8:36 am

Actually the secondaries are a floating AC circuit despite the fact that the speakers have a negative and positive terminal.

Rectifying this AC signal into a pulsating DC circuit often works.

The impedance of the speaker as well as the isolating diodes will reduce the combined over all impedance in the circuit, and the drive may continue.

Feed back into the other amps is not always a given.

The secondaries on a 75 volt system run with a lot of latitude, and most speaker isolation circuits do use diodes.

Externet · Post by **Externet** » Mon Jun 25, 2007 8:48 am

Do not dig yourself into a deeper hole trying to fix it, just accept the goofing and nothing will happen.

dacflyer · Post by **dacflyer** » Mon Jun 25, 2007 8:55 am

how in the world can you understand whats coming outof 6 radios at once ?

whats the purpose ? what sort of radios ? musik , communication , scanners ?

BTW i couldn't see your foto...the server must be down right now.

if it works i bet it will soundlike the collective hive of the borg...lol

i tried a dioad in series with a speaker once and it sounded like crap..
maybe i missed something ?

Chris Smith · Post by **Chris Smith** » Mon Jun 25, 2007 8:57 am

Sorry, it works.

Floating AC VS pulsating DC.

Reducing the impedance also works.

Stevereno · Post by **Stevereno** » Mon Jun 25, 2007 9:01 am

dacflyer wrote:how in the world can you understand whats coming outof 6 radios at once ?

Each scanner is dedicated to specific agency, and normally not all are active at the same time. At present, I use 6 external speakers. I'm just looking to conserve on space.

dyarker · Post by **dyarker** » Mon Jun 25, 2007 9:57 am

"i tried a dioad in series with a speaker once and it sounded like crap..
maybe i missed something ?" It would sound fine to a certain someone with crap between the ears.

Stevereno,
Don't use 75V transformers, do use 8 Ohm/4K Ohm transformers. Lower lead of 4K side of all connected together to common. The 6 upper leads are each connected to a 4.7K Ohm resistors (6 resistors). The other side of the 6 resistors are connected together to the inverting input of an amp IC. Another resistor is connected from amp output to inverting input. That makes the inverting input a virtual ground. Each scanner is loaded by it's characteristic impedance (almost), and no signal from other scanners get fed back.

6 low power audio transformers, a wall wart and 1 or two ICs is bound to be A LOT less expensive than 7 75V audio line transformers; and it will work MUCH better.

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

Cheers,

jwax · Post by **jwax** » Mon Jun 25, 2007 11:45 am

I'd go with dyarker- a mixer is what you need. Only question is if you can get the audio power you want out of the one speaker.

(hehe-crap ears-hehe)

Stevereno · Post by **Stevereno** » Mon Jun 25, 2007 1:34 pm

dyarker wrote: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.

Externet · Post by **Externet** » Mon Jun 25, 2007 1:53 pm

Until a better schematic shows up ;

R1+------10K---------S-------->AMP SPK
R2+------10K---------S
R3+------10K---------S
.
.
R6+------10K---------S

R1+ means radio 1 speaker + terminal. etc
S is the sum node, all S tied together fed to the amplified speaker input.

Miguel

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6 Radios to One Speaker?

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