Looking for Simple 12V supply dual opamp for kid's project

[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.

 

[paulb]

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.

 

[lineup]

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.

 

[paulb]

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

 

[chipco3434]

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.

 

[chipco3434]

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?

 

[paulb]

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.

 

[chipco3434]

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!"

 

[lineup]

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.

 

[Christer]

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.

 

[carlosfm]

LM4756.
DC controlled volume.

 

[chipco3434]

LM4756.
DC controlled volume.

Cool chip but the voltage requirements pushes the project into relatively more expensive surplus power supplies.

 

[lineup]

How about TDA7266 in my post above?

For 2x7 Watt I would recommend a DC supply
minimum rated 12VDC and 1.5-2 Ampere.


If you buy a trafo for 2x7 Watt at like 12 VDC
I would say you should buy
one transformer 9-12 Volt AC, rated 30VA or more

 

[paulb]

If you manage to find it

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

Digikey sells it. That's a good choice too.

 

[chipco3434]

How about TDA7266 in my post above?

I ordered a couple... Mouser has them also... six bucks & in stock

Thanks!

 

[chipco3434]

The suggestion of ac supplies is OK but this project has to be completed in 2 x 2 hour sessions... lest it drag on in perpetuity. The addition of AC/DC PS would lengthen the project time and add a little somethin'-somethin' to the lethal voltage quotient. It's not exactly electronics that young men devote their thoughts to... at least I do recall that to be my personal experience.

 

[lineup]

I understand, chipco3434.

Whatever 12 Volt you use, and if use of 8 Ohm speakers,
supply should be able to give 1.5 Ampere of current.
If you have to use 4 ohm speakers I would say 2.0 Ampere.

If you read datasheet of TDA7266, it is internally limited at 2.0 A (probably per channel)
and short circuit protected..

Heatsink for mounting IC does not have to be big.
1 mm thick aluminium and size like 3" x 6" might do.
I am sure you will find something.
Chip is also thermally overload protected.

 

[digi01]

tda1521

 

[chipco3434]

Thanks to everybody for the great suggestions!

 

[JesseG]

Hey Chipco:
Since nobody has yet mentioned it, I suggest you take a look in just about any IC mfgr's list of Automotive audio devices.

National, Pillips, TI, you name it... they about all make single-chip audio pwr stages for car stereos. Some of them have some pretty sophisticated features, too.

They are generally cheap (due to large numbers made) and easily implemented. I have seen a few with only 6 or 7 external components.

Best part - they are all made to run reliably off nasty, unstable power sources.

Good luck

Jess