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Discussion Starter · #1 ·
I would like to take some of my props and cut the leads to the speakers and plug them into an amplifier to use with better speakers. I have had mixed results. it seems like all the Gemmy props get distorted when I try this. Some other proms sound fantastic. I assume that there is an amp in the ones that don't work that has too much gain to be further amplified? Is there some sort of buffer I can build that will fix this situation?
 

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There are a few different things that can cause problems - the easiest way I know to deal with them is to put an audio transformer between the prop and the amp. Radio Shack makes one that I've used several times in situations like this. I don't remember the colors off hand (I'm at work & don't have one here) but you connect the output from the prop to the 8 ohm leads (doesn't matter which wire from the prop goes to which 8 ohm lead) and connect the other wires from the transformer to the amplifier. If I remember correctly (big if...) there's a wiring diagram for the transformer on the packaging.
 

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You could try a "quick and dirty" audio volume circuit.... there are various levels of complexity.

The simplest/cheapest is a resistor-divider network...

Spkr - >----VVV1k OhmVVV----------(Tap signal here)---------VVVV10k OhmVVVV---- <--Spkr +

(Pardon my text based Crap-O-CAD, lol)

Would divide the audio signal down by 90%

5k/5k would halve it (50%), etc.

A slightly more expensive option would be to use a potentiometer like this:
http://www.radioshack.com/product/index.jsp?productId=2062357

And hook the prop soeaker output to both the outside leads. The center ("wiper") lead would go to your amp and the speaker - to the amp ground.

From there, you could look up Op-Amp circuits and some other options but that will probably get you going anyway.
 

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Without being an audiophile or particularly knowledgeable on the gemmy stuff, I can only offer a few thoughts:

Is the prop actually driving a speaker or is it one of those piezoelectric disks? Speakers / voice sounds should be OK, but many of the piezo disks are run off an electronic square wave which might get really distorted going into an amplifier.

Does your amp have any type of input sensitivity adjustment or low/high level inputs? Sometimes this can help match it more closely with the given input.

Have you tried to see what would happen if you have the prop speaker hooked up AND tap off the inputs for the amplifier? I wonder if the circuit for the prop might be so simply/cheaply designed it can’t work with only amplifier impedance across the outputs, but would need the speaker for the proper impedance?

Does the prop circuit look like it has an amplifier section? If so, you might be able to tap the input to that amplifier (instead of it’s output) for the input to your amplifier.

As a last resort, if over driving is the issue, it seems like a simple resistor would help attenuate some of the power going into your amp? Though you might have to stick with a film resistor as opposed to a wire wound resistor which might further act as a filter in the audio circuit.
 

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Discussion Starter · #5 ·
Thanks for the ideas, I guess I will start with the transformer idea and work my way through the list.

I have a backup plan if I can't get it to work, but I would like it to work.
 
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