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Old 2nd April 2007, 05:54 AM   #1
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Default Loudspeaker Amp schematic needed

I am looking for an amp that shoudl be pretty easy to build, as well as will power an 8ohm loudspeaker. Its RMS rating is 25 wats but I dont think I will need 25 watts.

I am wanting to make this an amp that will power an electret microphone, that i can switch on and off, as the input and the 8 ohm speaker as the output. This will be installed on a motor vehicle(honda civic to be exact) as a PA system.

Any help is greatly appreciated.

PS: i am very compitent in the world of electronics. Before i built a preamp(LM386 based) that has worked very well for what i needed it for so I know how to put these things together; i can follow schematics very well.
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Old 2nd April 2007, 02:13 PM   #2
jaycee is offline jaycee  United Kingdom
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Hmm... you want it in a car, so you will want it to run from 12V. I'd look around for some "car audio" type chips, ST make a lot of them. The example schematic in the data sheet for them should be fine. You won't get 25W into 8 ohms from 12V directly, though.

You may want to stick a preamp before this that deals with the elecret mic. This should be easy enough to do with an opamp.
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Old 3rd April 2007, 05:53 AM   #3
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there are several that will do about 25w bridged
here's one of them.....

http://www.microsemi.com/datasheets/lx1725.pdf

i think NS makes a couple, and we're still talking analog..... there's a bunch of D and T amps as well.....
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Old 3rd April 2007, 10:32 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
make sure the pre-amp is insensitive to car noises, ignition, alternator, etc (=very good PSRR).
The amp similarly should have a good PSRR.
If the microphone is only for voice then maximum intelligibility can come from narrow banding the amplifier and pre-amp.
In the extreme this could be as close as 300Hz to 3kHz, but 200Hz to 5kHz will probably sound more realistic.
If the mic is used close up, then consider adding an adjustable bass cut to remove the boost that close micing gives.

What are you using for a speaker? A horn could probably manage with just a few watts. Remember the PA horns used at school sports day, running on tiny batteries.
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Old 3rd April 2007, 04:40 PM   #5
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the closest pic i can find is this one, its the exact one but its halfway cut off. its an 8-ohm, 25-watt(rms) powerhorn.
Click the image to open in full size.

how many watts do you think I should need for this?

I know about the noise on the pre-amp when i built it. it picked up every noise possible. I went and got a 12v+ noise supressor and now it works like a champ


are there any really simple amp schematics out there that would work with this that would be loud enough?

Also is there any of those PA system microphones out there that the amp would only be powered on when I press the botton on the side?
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Old 7th April 2007, 04:10 AM   #6
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any ideas?
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