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Old 20th January 2006, 03:03 PM   #1
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Default Looking for Simple 12V supply dual opamp for kid's project

I am looking for a suggestion for a simple dual opamp to run mono-polar from 12VDC. Would like the output to be about 5 watts. I would like to run the amp from wallwart.
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Old 20th January 2006, 03:28 PM   #2
paulb is offline paulb  Canada
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Do you mean a 5 watt power amplifier? What does "mono-polar from 12VDC" mean?
Take a look at National Semiconductor's LM384. They have lots of other choices.
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Old 20th January 2006, 03:42 PM   #3
lineup is offline lineup  Sweden
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Default Re: Looking for Simple 12V supply dual opamp for kid's project

Quote:
Originally posted by chipco3434
I am looking for a suggestion for a simple dual opamp to run mono-polar from 12VDC. Would like the output to be about 5 watts. I would like to run the amp from wallwart.
12VDC will theoretically supply an AC-signal of +-6 Volt peak.
Due to losses in transistor and circuit, we can not expect much more than +-5 Volt.

Power = (peakVolt x peakVolt) / ( 2 x loudspeaker impedance in Ohm )

For 8 Ohm loudspeakers we get max power:
P = 5 x 5 / ( 2 x 8 Ohm )
P = 1.5625 Watt

For 4 Ohm LSP we get
P = 5 x 5 / ( 2 x 4 Ohm )
P = 3.125 Watt

If you parallel two 4 Ohm = 2 Ohm we get:
P = 5 x 5 / ( 2 x 2 Ohm )
P = 6.25 Watt

Now 3 Watt into 4 Ohm is not too bad for a small system.
It gives more loudness you would expect from a small number.
Especially if your loudspeakers have a good efficiency.
Some of those small loudspeaker systems for computers
have only like 2 Watt output.

I can not recall a 12VDC amplifier circuit.
But sure it can easily be done.
And there are most likely several suitable 12 VDC chips, IC (integrated circuits), around.
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Old 20th January 2006, 03:56 PM   #4
paulb is offline paulb  Canada
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My company is building a bunch of boards based on an LM4752T. This is a stereo amp that will run nicely from 12VDC. We may be selling these boards to interested constructors for a reasonable price (not to make money, just to raise some publicity). It will run from a wallwart and will be sized to fit a cheap readily available enclosure. If you can wait a bit, this may be a good solution for a beginner's project.
See http://www.national.com/ds/LM/LM4752.pdf#page=1
The board also includes a differential receiver intended for
distribution of audio signals; that's what we will use it for here.

If you want to build something a little more challenging, take a look at
http://www.redcircuits.com/Page33.htm
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Old 20th January 2006, 04:01 PM   #5
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Thank you lineup and paulb.

LM384 would be ideal and could be done in dual mono. By mono-polar, I mean 0/12 supply. Not -12/+12 supply.

I think 2 or 3 watts would be fine. The kids built some ~92dB speakers last year so there should be some decent volume from that power level.

So, now all I am looking for is something on the order of a 384 in stereo.
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Old 20th January 2006, 04:11 PM   #6
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paulb...

Thanks. 4752 looks like a contender. The discreet is too much for a first time project as the adults involved would be challenged to TS the circuit.

I think 4752 would provide plenty of power. It would only be limited to finding the right wart on the WWW junkpile. I reckon that a 12V-15V ~ 800~1200ma would be ideal, eh?
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Old 20th January 2006, 04:50 PM   #7
paulb is offline paulb  Canada
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I'll post something when I have more details on the boards we're building here. We'll have to try it out before selling any, of course.
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Old 20th January 2006, 04:57 PM   #8
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I have 4752 samples on the way!

Thanks.

I will start mining the back room for suitable warts. Like my partner says, "If you think that junk's valuable then we're sittin' on a gold mine!"
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Old 20th January 2006, 05:04 PM   #9
lineup is offline lineup  Sweden
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If you manage to find it

TDA7266 from SGS-Thomson
7+7W DUAL BRIDGE AMPLIFIER

By using bridge they manage to get stereo 2x7 Watt into 8 ohm loudspeakers from only 11 Volt DC supply.
Distortion figures looks low, so would have a nice sound.

TDA7266 Datasheet PDF download

It is a 15 pins multiwatt IC for Stereo, with few external components.
Has also got pins for MUTE and STANDBY.
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File Type: png tda7266.png (40.6 KB, 448 views)
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Old 20th January 2006, 05:13 PM   #10
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Don't forget that you could also use half-wave rectification to get +/-12V from a single AC secondary, but you will need larger caps, of course.
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