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Is this an amplifier that could take a speaker level input?

579 Views 9 Replies 3 Participants Last post by  custommadename

Just wondering if this requires a headphone jack/composite cable and comes out as one but louder, or can I feed the speaker line into it and hook up a speaker directly to the output. Thanks!
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It has a temrinal block as the input and a terminal block at the output. It could, with about $3 from your local Radio shack.

Run wires from one of the parts i linked you to into the terminal block on the input

http://www.radioshack.com/product/in...ductId=2103452 OR http://www.radioshack.com/product/in...ductId=2103454

Hook the speakers directly up to the terminal block on the output.
Nice links, thanks! But does that mean I'd absolutely not be able to run a speaker signal into it (+/- to a cone, basically) and would have to go with a composite/headphone signal (L channel / ground) for the input? I'm trying to amplify a speaker signal from a thing that doesn't have a composite or headphone jack output. It's a button that when pressed plays into a small speaker, but I need that signal to go to a bullhorn.
All a speaker-level output is is a giant version of a line-level output . With an appropriate transformer, you can pad that speaker level output back down to something reasonable for a simple opamp like you've linked to, but the transformer required to do that would likely my much more expensive than the amplifier itself. Simply using a ton of resistance won't be great, as you can easily overload the first amplifier's outputs. As for the output of this amplifier itself, taking a look at the schematic we can see that the resistor in parallel with the output is 10ohms. That will change depending on frequency because we also have a capacitor in the same 'branch', but in general we can say that 10ohms is close enough to "speakerland" that this circuit could be used to drive a speaker with no problems, even if the designers did not tell us so.

Getting past that hurdle, take a look at the opamp's datasheet - scroll down the the 'electrical characteristics' section. The maximum output power is going to be limited by the voltage supply rails (simple physics; you can't output more power from a circuit than you're supplying to it). When the supply is a relatively reasonable 9v, peak output power is limited to about 1/3 of a watt. It'll make sound, but probably not as much as you'd like unless you're using an incredibly efficient speaker. How loud does this need to be?

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Yes! If I could give you some rep, I would! If you're ever in Indiana, come by for some free alcohol or something of the sort.

At 1/3 W, that probably is going to suck. I simply need a bullhorn to be louder. From what I can tell, the bullhorn is a regular speaker in a shell. I'll take it apart again to look at the speaker specs. The first time it was taken apart, it was hooked up straight into the button, and though it works and is louder than the button's original speaker, it just doesn't have any oomph.
Typical 'bullhorn' type devices are whats called a compression driver, not a typical speaker as you're probably thinking of it. The compression driver works by forcing sound pressure through a small opening, then (almost always) using a horn to control the directionality of the output.

Now, a compression horn system can be incredibly efficient, sometimes well over 110dB of output at 1m with just a single watt of input - it depends on your exact hardware, though. If you've got sensitivity of, say, 110dB for your particular speaker/horn combo, you could still, even with this puny amplifier, get about 105dB of output at 1m. That may, or may not, be enough for you. If you need to be really loud at short range, it might be fine - but those tricky laws of physics dictate that we loose 6dB of level for every time we double the distance from the source. At 2m out, you'd get (roughly) 99dB; 4m out 93dB, etc.
This is awesome stuff! How much more can be known once I get the bullhorn taken apart? It's not here right now, but probably tomorrow I'll have it in pieces.
Originally Posted by custommadename;13106200
This is awesome stuff! How much more can be known once I get the bullhorn taken apart? It's not here right now, but probably tomorrow I'll have it in pieces.
Well, a model number and such would be a great start.
Really anything you can use to identify it, perhaps even the model of the compression driver itself.
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Sorry custommadename, i originally misread your original question thinking you wanted a headphone jack. I also did not know you where driveing a bullhorn.

I just facepalmed myself. I will be graduating with a degree in Electronic Engineering in May. I knew everything that Chipp was talking about, i just did not think the problem through all the way.

The item you picked out on ebay could easily drive a headphone speaker, but nothing bigger than that.

Even though a compression driver would be better for your application than a standard audio power amplifier, i think a audio amplifier would be cheaper and easier to find. Compression drivers are a bit of a specialty item.

Here are some ideas:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=127255&productId=127255&keyCode=WSF&CID=GMC 7 Watts $17

http://www.amazon.com/Sure-TPA3123-Class-D-Audio-Amplifier/dp/B003XRMBJK]Amazon.com: Sure 2x8W @ 4 Ohm TPA3123 Class-D Audio Amplifier Board: Electronics[/URL] 8 Watts $15

http://www.sparkfun.com/products/9612 38 Watts, $30

These require a external power supply, but you could easily modify them to connect to a computer power supply. (or any other power supply for that matter)

Hope i was helpful.
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Thanks! I am going to be home at 10 PM EST, and then I'll take apart my bullhorn. Those are some awesome links even for regular speakers, though. Amazon had a quick link to a Sure 2x15W amp that seems like it could make some sense as well. Assuming I have a couple bullhorns mounted inside my fenders on my car, how loud should I need the bullhorns to be to have the button's thingie heard over regular engine idling noise?
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