questions on Class B audio amplifier

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mrdarrett 17 years ago

I took a look at this:

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It appears that this unit's max continuous power output on +/-12VDC at

4 ohms is 18W, if I calculated that right...

I wanted to build it, but I realized that increasing the voltage much beyond +/- 12V would exceed the TL082 op amp's maximum voltage spec.

If I used a couple of higher-voltage TLE2141Cs, good to +/- 22V, would this give a max continuous output power of 60W?

Since this is class B, and not Class AB... does the first op amp in the schematic above do a good job of removing the "dead time" between crossover? THD < 1%?

Does this Class B amp waste less power than Class AB (since only one transistor is on at a time)?

I'm guessing that all the "junk" (input stage, VAS) between the line input and output transistors on a typical power amplifier schematic serves pretty much the same purpose of the two op amps here...?

Thanks,

Michael

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Jamie 17 years ago

Look at using a LM1875 Ic amp, that chip starts at 16 Vcc up to 60 Vcc.

if you drive it with a complementary supply, then it's 8..30 Vcc/Vee etc.. This chip does 20 Watts and can source/sink 4 Amps. that's enough to drive some heavy complementary trannies.

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Eeyore 17 years ago

Why do you waste your time like this ?

Please become an adult.

Graham

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Phil Allison 17 years ago

** Nope - it is actually much less.

** Not a snowflake's chance in hell.

** No to both.

** Not when delivering any power into a load.

** It is a complementary BJT follower /current booster tacked onto the output of an op-amp.

Good of a couple of watts of lo-fi.

You are UTTERLY clueless.

..... Phil

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John Fields 17 years ago

Same old shit, eh, Graham? The guy is obviously having some difficulty wrapping his head around a problem and isn\'t afraid to admit it, and instead of giving him a helping hand, you give him a slap. What a really mean bastard you are. JF

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Tim Wescott 17 years ago

Always show your assumptions.

You're assuming you can get 24V p-p out of that circuit -- review the base-emitter drop of a transistor, and the voltage drop of the op-amp before you make any promises.

See my comment above. Yes, but (but this is not the way to achieve that!!!)

Read the web page. If you have an oscilloscope to measure output -- try it. If you don't, try it out on LTSpice (which is free). Use their "generic 1-pole op-amp" with a GBW to equal the TL082, and try it at different frequencies.

In theory, yes, in practice -- what's your operating point? What class AB amp are you comparing it to? What frequency signal are you pumping through?

Yes, but a typical power amp sounds better....

Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html

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Eeyore 17 years ago

Yes but it sounds s*it.

Graham

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Eeyore 17 years ago

Nothing compared to you.

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Eeyore 17 years ago

And Universities are turning out kids even stupider than this !

Graham

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John Fields 17 years ago

You calculated it right, but the TL082 isn\'t a rail-to-rail output opamp, so the output into the emitter follower pair would be considerably less than 12V resulting in, consequently, less than 18 watts CW into the four ohm load.

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Phil Allison 17 years ago

"John Fields"

** Lets see what it *really* is then:

From the data on the TL082, with +/-12 volt rails and say 500 ohms load, the available output swing is +/- 7 volts.

Equates to 14mA peak.

From the data on the TIP41, Hfe = 50typ at Ic=1A & Vce= 4 volts.

50 times 15 = 700mA.

700 mA into 4 ohms = 2.8 volts peak.

Or 1 watt, rms continuos.

Long, long way from 18 .........

...... Phil

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John Fields 17 years ago

So, you admit you\'ve met your master? For years now, in an effort to try to communicate honestly, I\'ve tried being kind to you, and cordial, and courteous, and objective, and logical, and even friendly, but it seems that\'s all come to naught since all you\'re interested in is denigrating anyone who brushes up against your holy space and questions your opinions. JF

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John Fields 17 years ago

RMS? ;) JF

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mrdarrett 17 years ago

Ah, numbers... goodie...

Where did you get 500 ohms for load?

Yep...

Thanks,

Michael

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Phil Allison 17 years ago

** See above.

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Eeyore 17 years ago

You just described yourself beautitfully.

Graham

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Eeyore 17 years ago

It's a total heap of garbage. It's almost beyond a joke. If the rest of the site is like that then try to forget anything you 'learnt' there.

Graham

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John Fields 17 years ago

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Why, thank you Graham! And how do you think I described you? Beau_tit_fully as well? Freudian slip: When you say one thing but mean your mother. JF

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John Fields 17 years ago

My, my... A blanket condemnation, but nothing to back it up with? How typical of you! JF

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John Fields 17 years ago

Yup. Nicely done. Thanks! :-) JF

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