6 Radios to One Speaker?

[MrAl]

Hi again,

dyarker:
First, why would you add all those transformers?
Second, the output needs a audio power driver ic to drive a speaker
properly.

[dyarker]

For isolation if needed if the straight resistor mixer didn't work (like differential signal to speaker out vs signal and common). (see a couple of posts back)

He said he had a Motorola amplified speaker (a couple pages back), so power stage not needed.

It is hard to keep straight who is doing what and why; when what should be a 2 page thread becomes 5 pages due to Chris and positronicle many times, and Chris and everyone else once each!

Chris also asked about where the power stage was. I was going to ignore that because he's still talking about 75V, which was dismissed on page 1!

You took a try at explaining the rectifier business to him. See how far that got you?

Cheers,

[MrAl]

Hi again,

Mr Al
Nice bit of energetic work on your part. But why would you even waste your time on such a ridiculous reply. Even a first year electronics student would have tossed this aside after the first post.

Well, after considering that the higher frequencies doent get affected
as much it seems it might work to some degree, although i would not
want to use it for high quality music that's for sure


dyarker:
Well, instead of all the transformers could you try a cap from each
radio ground to a common ground? In other words, put the cap in
the ground circuit instead of in series with the input resistor (for
each radio).
This would look something like this:

Code: Select all

          -----------R----------common_input
radio 1
          -----------C----------common_ground

          -----------R----------common_input
radio 2
          -----------C----------common_ground

All the outputs get tied in parallel of course, then go to the op amp.
I think you were using 10k for each R, and 0.1uf for each cap seems
reasonable.
If any of the radios grounds get tied together because of perhaps a
common power supply, then another cap in series with each R would
be required. This would mean two caps for each radio, one in
series with the ground and one in series with the resistor.

[dyarker]

Yeap, that'll work too!

Perhaps I got a little fixated on transformers to give isolation. The 8 Ohm to 75V ones mentioned on page 1 are probably $10 to $20 each and there would have been problems with the scanners driving each other's outputs. The ones I selected are $1.50 each. You suggest capacitors at like $0.30 each. Yes, use the cheapest solution that gets job done.

C U L Al

[Stevereno]

dyarker, MrAl...

I do use a common 12vdc supply for all the scanners and plan to use the same supply to power the amplified Motorola speaker. If I understand you both correctly, I should have things setup as indicated below, right?



I truly appreciate all your help.

[Chris Smith]

The reason I asked about power is no one at that time [you hadn’t finished your post in full] included a “Powered Speaker Systemâ€

[rshayes]

You should check the scanner outputs to insure that one lead of the output is grounded. They probably are, but checking never hurt. An ohmmeter can be used for this check.

If one lead of the speaker is grounded on the scanner outputs and if the same power supply is used for the scanners and amplifier, you don't need capacitors in the ground leads from the scanners. These will already be connected together through the power supply return.

If both of the speaker leads from a scanner are ungrounded, the speaker may be "bridged" between two amplifiers. In this case, you may need to use transformers. Mouser sells small 500 ohm to 500 ohm transformers for about $2.20 each. These cover the voice range only (300 to 3000 Hz) but the frequency response of the scanner may not be much better than that.

[GoingFastTurningLeft]

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.

If its a scanner... couldn't you just scan 6 preset channels? Or do your scanners not have preset scan?

I know my bearcat scans something like 100 presets a second.

As far as getting them out of 1 speaker, i'd recommend a 6-way active audio mixer with an amplifier, since they're probably all outputting at audio line level (1V pk). I would not recommend a diode . You'd be clipping half the waveform that way. No way that could sound good at all, especially with a signal that isn't exactly high-fidelity to begin with.

*I admit I only read the 1st page. Looks like you've got everything figured out.

[Stevereno]

So, do I have this diagram right? And if so, are simple carbon resistors and ceramic caps a good choice? Just looking for affirmation before I build this project. Thanks.

[dyarker]

Try it from one scanner first. If you can't get enough volume try changing the 10K resistor to 4.7K (or two 10Ks in parallel). If voice sounds too treble and not enough bass, change 0.1uf caps to 0.22 or 0.33uF.

When one sounds right, then add second scanner with same value components. If that works okay, should be good-to-go for other four scanners. Cost for experiment two or three resistors and four caps (which you can reuse in permanent set up) and some scrap wire and maybe a little black tape. Just twist leads till you're happy with sound quality. Maybe thumb tack it to an old piece of wood or cardboard to prevent accidental shorts.

Nothing critical here! Any resistor type, any tolerance (5%, 10%, 20% (1% would be overkill unless you've got some just laying around)). Same with caps; ceramic, poly or mylar; 25V or higher rating (16V would work too).

Cheers,

[Stevereno]

Thank you much!