Signal amplifier works

Anyone who uses 'righttard' is beyond help if the answer isn't part of the DNC mantra, or his well worn KKK handbook.

He's like the knuckle dragging moron on "Big bang Theory" who said, "That's what I lie about science. There's not just one right answer." He doesn't know a damn thing, yet he thinks he matters.

Reply to
Michael A. Terrell
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For educational purposes as well as tweeter break-in, here is a good compromise solution: Use an op-amp for the front end of your power amp, and just build the power output stage. I'd recommend using a "real" op-amp, even a lowly

741, on separate pos and neg supplies. The single-supply units tend to be much more difficult to apply for decent audio, and you don't need that kind of distraction just yet.

Note also that traditional (ie not class D sitiching) audio power amps are really just op-amp circuits with beefy output stages. Once you get the the output working, you can think about delving into the differential input stuff, if you want.

So the basic idea is to first wire up a simple single op-amp stage. It can be inverting or non-inverting, though real audio power amps are almost always non-inverting. Get it to drive a dummy load of (say) 1-10k or so, viewed on your scope to see that it's working properly.

Now add the output stage. You can use a simple (but terribly inefficient) class A output. Break the connection at the op-amp output pin, so the op-amp is on one side and the feedback and load are on the other.. Connect up your NPN power (2N3055) base to the op-amp, emitter to neg supply, collector to the feedback and load. Also to the collector you need a power resistor to the pos supply. The value should be computed so that when the NPN is off, the R will be able to supply the actual (8 ohm or whatever) load at the max positive swing.

The output stage doesn't need to use the same power supplies as the op-amp, for instance if you have only low-current regulated supplies for the op-amp, you can use totally unregulated high-current supplies for the output. (Real power amps typically don't use separate regulated supplies at all, the whole shebang runs off the big unregulated supplies. But in your case you have to observe the voltage limits of the op-amp, typically +/-15. If you have unregulated supplies that stay below that, use them for everything.)

Next step: If you have a PNP power device, you can easily make this into a class B stage. Just replace the R between the NPN collector and pos supply with the PNP. The PNP collector goes to the NPN collector/load/feedback connection, the emitter to V+, the base to the NPN base/op-amp output.

This will be much more efficient, and would be ideal for your break-in purposes. The reason you don't see this true class B in real audio is that it has crossover distortion. At signal voltages near zero, both transistors "want" to be off. They each need several tenths of a volt to get going, but they need opposite polarities to do so... a problem since their bases are connected together. The huge internal gain of the op-amp can deal with this *fairly* well, since when the load needs to be (say) -0.1 V, it can apply -0.6 V (or whatever it takes) to the base to get the NPN to go on. But there are limits to how well it can do this, and you notice them at really low signal levels... not a problem at all for your break-in job.

True audio amps are typically class AB, which applies a bias to each output device to keep it out of the fully-off state near zero. This can be tricky, since it means both devices are on at the same time, and if you apply too much bias you can easily get them both hot enough to enter thermal runaway: A bit more heat causes more current to flow, which causes more heat.... (Bipolar devices have this problem, but not FETs, which is one reason why modern amps use FETs.)

Hope this helps!

Best regards,

Bob Masta DAQARTA v7.21 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusic generator Science with your sound card!

Reply to
Bob Masta

worst.

beginner

URL

the

circuits

and

Congratulations. You have won the discussion without sullying your argument with the faintest hint of a fact.

It is so helpful when you losers play your cards so quickly, making the inevitable 'plonk' decision that much simpler. Some of your marginally more intelligent peers are able to dissemble for days, even weeks before showing their true colours.

So. Anyone else want to step up and practice your logical and argumentative fallacies?

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
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Reply to
Uncle Steve

You're well known in other newsgroups as invincibly ignorant, so I suppose you may as well join "Joe Thompson" in the bozo bin. I'm sure you will be able to constructively occupy your time there with characteristic self-congratulatory self-promotion, secure in the knowledge that you're right and everyone else is wrong if they dare disagree.

As much as I'd love to compare our vast ignorance on every topic imaginable, I will happily cede that field to you.

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
 Click to see the full signature
Reply to
Uncle Steve

I may end up doing this, although I am still inclined to see what I can do with what I have on-hand. What did everyone do before op-amps were available?

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has a reasonably detailed home-brew project covering some of its development and testing. Figure three slightly resembles what I was initially working with, and figure four describes a complete solution, which may be adequate for my purposes.

The first thing I'm going to do is understand R/C networks better. The thing that's confusing me at the moment is the frequency-variance of circuits under load. I'm still coming to grips with the non-linearity of electronics, which essentially doesn't exist in computer programming.

With you so far.

You mean to say run the input stage off the low-power regulated supply and the output stage right off a bridge rectifier. Perhaps that is a good idea. I'm kicking myself at the moment for only picking up only one 12V torroidial transformer from the local surplus shop. If i had two, it would make a really beefy 24V supply. The 12V supply I was using is a much smaller wall-tumor (about 1A) that may have been struggling to heat up the original circuit. I was watching the P/S led on the regulated side fade out as thermal runaway got going.

True enough, most audio listening happens at power levels that should be a fraction of rated power. In this case, the driver is going to be beating against a bag of cotton balls or similar, and I don't give a rat's ass about THD. I've seen a few amp circuits with a NPN/PNP pair as you describe. I suppose it requires more negative feedback than otherwise to counteract the low-level distortion.

Does that mean the bias causes the two output devices will fight each other to stay near their turn-on threshold? As I said, this application is specific enough that signal distortion is really not a problem at the target output power. If there's 5% distortion, the only thing that's going to notice is the cotton-balls absorbing driver output.

I clarifies some of the web-material I've read. Thank you.

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
 Click to see the full signature
Reply to
Uncle Steve

Steve

worst.

that

electrons

beginner

speaker,

URL

worked,

a

the

circuits

can

and

depending

Ebers-Moll

My circuits work. Yours don't. What else can I say? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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Reply to
Jim Thompson

My first post used an OpAmp plus a power stage, just as Bob Masta proposes.

Discrete transistor designs... diff-pairs, plus level-shifters to single-ended for the output stage.

Here is my first OpAmp design... analyzed in detail...

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Designed 50 years ago (when I was 22), and still being sold.

Work your way thru the analysis.

[snip] ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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Reply to
Jim Thompson

According to the Copenhagen interpretation, wave functions collapse into reality when they are observed. Combine that with the many-universes concept, and I conclude that I have created my own universe of which you are a minor detail.

--
John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
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Reply to
John Larkin

Stop playing with turds.

Reply to
Michael A. Terrell

Oh yeah? I have a doomsday device and I fully intend to keep destroying the universe until I get you. So there.

(p.s. please don't tell the DHS. Thx.)

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
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Reply to
Uncle Steve

The math...

--
"For a successful technology, reality must take precedence  
over public relations, for nature cannot be fooled." 
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Reply to
Fred Abse

I've been battling (in the local newspaper opinion page) a village-idiot liberal anti-gun type who thinks that Lott's hypothesis that a 1% increase in gun ownership causes a 3% reduction in crime rate is a LINEAR relationship :-(

(Related to my difference equation post :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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Reply to
Jim Thompson

Sorry! My apologies! I should remember to do as I say :-( ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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Reply to
Jim Thompson

Bwahahahaha ha! Good one! ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
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Reply to
Jim Thompson

"Math is hard" -- Barbie

The site I was referencing has a number of articles that look good at first blush:

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for one, which I'll have a go at as I work through his introductory articles.

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
 Click to see the full signature
Reply to
Uncle Steve

There are just as many problems on both sides of the street, avoiding one isn't going to make the other better.

In actuality, OP-AMps are easier to work with. You need to get a few basics down and you'll see why.

Look for an "Ideal Op-Amp". Most articles should also cover the aspects of a op-amp in real life over the ideal one, so you'll have a better understanding as to why things are done as they are.

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Take a look at that.

Jamie

Reply to
Jamie

Well, just don't take it as carry-on.

--
John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

"We are not going to the moon because it is easy, we are going to the moon because it is hard" John F. Kennedy.

--
"For a successful technology, reality must take precedence  
over public relations, for nature cannot be fooled." 
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Reply to
Fred Abse

I don't have to. I simply destroy universes until I teleport to where I want to go.

And now for my next trick, a vacation in sunny Havana.

Regards,

Uncle Steve

--
More than a century has passed since science laid down sound 
propositions as to the origins of the universe, but how many have 
 Click to see the full signature
Reply to
Uncle Steve

is

electron

deliver

on

first

Like all lefties, you're illiterate and incapable of thought.

Reply to
krw

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