audio amplifiers: +/- X VDC vs 0-X VDC

On Sep 25, 11:33 am, snipped-for-privacy@gmail.com wrote: > I've noticed some audio amplifiers, like this one, need +/-

Split supplies don't require an output capacitor on the amplifier. Those can get big and expensive for high power levels.

GG

If you have two amps running from one power supply and one is inverting, they call that bridge mode. One terminal goes up and the other one goes down. If there's no audio they both sit at the halfway up point. Used to be that would come out on a phone jack or a bananna plug, but the Europeans got worried and made everyone use Speakon connectors. So now we are all safe.

If you look a little closer at the PDF file, you'll notice that the voltage range is not locked at 35 volts. It'll operate down to

And as for the question about you speaker output center point. If you look at the how they label the power supply lines and also include a ground symbol in the print. This means the chip is expected to be connected to a dual out put supply with a common ground. the output will have differential polarities. + & - and a common. when the IC is at the center axes point of the signal. the + and - sides are equal and thus cancel each other out.

If you were not using a dual polarized rail supply, then you would have problems because the design would force you bias the IC so that the output is generating 50% of the supply voltage. In this case, you'd need a decoupling cap.

It's best to use a dual rail supply so that you don't use a cap on the output. Caps change value over the spectrum and thus can inductively interact with other components on the line. This does not do well for achieving a flat response!.

Because audio requires both positive and negative pressure variations and that's most readily created by appling positive and negative voltages to a loudspeaker.

They AC couple the signal to achieve the same thing. This requires extra components etc.

The speaker moves BOTH ways. NO, you don't apply DC to a loudspeaker for zero signal. You'd burn out the voice coil for one thing.

Graham

No, you'd need a COUPLING capacitor.

Graham

Ignorant sap sucker.

Go back and count your marbles, I think you've lost some.

Some of this is illusion. You can have a dual supply for an op-amp or audio output amplifier, and then the "resting point" is at zero volts.

But you can have the same circuitry running off a single supply, but then you need to bias the opamp or output amplifier so it rests somewhere in between the positive voltage and ground, often right in the middle. It gives you the same effect, the only difference is really where you measure the voltage from.

With a single supply opamp or audio amplifier, your DVM's negative lead going to ground would show the output voltage to be 1/2 the supply voltage (we're generalizing here). But, if you put your negative lead to the point that biases the opamp or output amplifier, and then measure to the positive supply (ie put your positive lead on the positive supply bus), you'd find half your DC voltage. Connect the positive lead to the ground of the amplifier, and you'd read a negative voltage, equal to the value you saw at the positive line. (This is assuming the opamp or output amplifier is biased at the half-way point.).

How do you get a negative voltage when you aren't powering it with a negative voltage?

It's all a matter of reference point. In both cases, you have your ground lead at a point somewhere between the supply lines. Both basically give you the same effect.

But of course, if you bias the amplifier input at half the supply voltage, you only get the swing of the supply voltage (likely a bit less). ANd the resting point of the output will be half-way between ground and the positive supply. You can't connect that to the speaker, the DC voltage will cause problems. Return the other speaker lead to the same bias voltage, and that DC component goes away. Of course, then that DC voltage at 1/2 the supply voltage will have to handle the current of the output stage. Or, you can go the normal way, putting a coupling capacitor at the output, which strips off the DC component.

You will need higher voltage if you want more power, and at that point it likely is worth adding a negative supply rather than double the voltage and dealing with the DC component on the output.

As someone pointed out, another method of getting rid of the DC component is to feed the other side of the speaker with an out of phase audio signal:

Audio ---------------AMP1 -- | speaker |--inverter----AMP2---

Both leads of the speaker sits at the same "resting point", ie half the supply voltage. So it's not seeing a DC component. But since there is an inverter stage between the audio signal and the speaker, the audio signal to the speaker is different on each speaker lead, and the audio comes through.

Michael

I think it's time you went back to school.

Do you EVER get anything right ? Typical bloody 'think he knows it all' programmer. Scum of the earth you are.

Graham

There is nothing wrong with using a wrong term, but why show your ignorance over it by arguing when someone corrects the term? It is, after all, a coupling capacitor.

Yes, that is true, It's also termed Decoupling capacitor because of the interaction of what it's used in. Coupling a circuit via a capacitor is just that, coupling. how ever, using a CAPACITOR to isolate DC voltage (which is where the original contents of this started) is termed as Decoupling capacitor which is more to describe in what it's doing and not what it is.

Any one that has really been working in the field knows this how ever, I find those that just sit there arm chair wise and recite text book literature and proclaim to be experts are just ignorant to say the least.

Graham, or is it Mr. HAM? the little snake in the grass.

It's not called anything of the sort. You're just making stuff up as you always do when (as usual) your mistakes are found out.

Utterly WRONG.

You can call it a DC blocking cap OR a coupling cap. But it is NOT a *decoupling* cap !

You are the most monumental moronic f****it.

" In electronics, decoupling refers to the preventing of undesired coupling between subsystems via the power supply connections. Nowadays, this is commonly accomplished by connecting localized capacitors close to the power leads of integrated circuits to act as a small localized energy reservoir; these supply the circuit with current during transient, high current demand periods, preventing the voltage on the power supply rail from being pulled down by the momentary current load. See decoupling capacitor. "

Graham

Wow. Is your mother a regular lurker on the board?

Oh well...............

It's making sense now!

Thanks everyone

Michael

Geez! Inverted is not equal to "out of phase". They're precisely in phase, simply of opposite polarities.

Please don't confuse the newbies.

Thanks, Rich

Not to mention that both are 'sitting' on exactly the *same* DC level (not opposite).

Graham

Ha

So which part are you taking issue with?

"Your stereo speakers are out of phase", but wait, reversing one pair of wires will remedy the situation. Both speakers are now pushing out at the same time.

Stick an inverter in there, and it does the same thing as the reversed wires.

So it's my use of "inverter"? My Radio Shack dictionary gives the same basic definition for "inverter" and "inverting amplifier".

If you don't have a 180 degree inversion there, then the speaker sees no difference between the terminals no matter how much sound gets pumped into it. Because the ac signal on both leads of the speaker is the same. It cancels in the same way as the DC on the two amplifier outputs cancel.

Take two LM380 audio amplifiers, feed the audio signal to the non-inverting input of one and the inverting input of the other, and you get the same effect. It doesn't matter what DC voltage is on the output, since each device rests at the same point. But since one is an "inverter" for the audio signal, one of the 380's output is going more positive while the other 380's output is going more negative, which feeding the speaker puts an AC signal across it.

Michael

Given this signal:

/\\ /\\ /\\ / \\ / \\ / \\ _____/ \\_____/ \\_____/ \\

This is inverted: _____ _____ _____ \\ / \\ / \\ / \\ / \\ / \\ / \\/ \\/ \\/

While this is out of phase:

/\\ /\\ /\\ / \\ / \\ / \\ / \\_____/ \\_____/ \\_____

While with a pure sine wave signal it's pretty much equivalent (except for noise on the line), audio is not a pure sine wave.

Note that the difference is VERY important when dealing with three phase motor control, or R/C/L filters.

To be totally accurate it's not a phase shift but a polarity inversion (of the audio part of the signal only).

IF AC coupled. Choosing an IC that is designed to be AC coupled is highly disingenuous of you as it obscures the true operation required. Casual readers might not know that about the LM380.

Graham