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

I've noticed some audio amplifiers, like this one, need +/- 35VDC:
http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to ground:
http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/- power,
and the other is happy with 0-X power?

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the available
speaker movement range?

Michael

 

On Sep 25, 11:33 am, mrdarr...@gmail.com wrote:

I've noticed some audio amplifiers, like this one, need +/-
35VDC:http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to
ground:http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/-
power,
and the other is happy with 0-X power?

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the
available
speaker movement range?

Michael

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

GG

 

[BobG]

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.

 

[Jamie]

mrdarrett@gmail.com wrote:

I've noticed some audio amplifiers, like this one, need +/- 35VDC:
http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to ground:
http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/- power,
and the other is happy with 0-X power?

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the available
speaker movement range?

Michael

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
20 volts.

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!.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Eeyore]

mrdarrett@gmail.com wrote:

I've noticed some audio amplifiers, like this one, need +/- 35VDC:
http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to ground:
http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/- power,

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

and the other is happy with 0-X power?

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

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the available
speaker movement range?

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

 

[Eeyore]

Jamie wrote:

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.

No, you'd need a COUPLING capacitor.

Graham

 

[Jamie]

Eeyore wrote:

Jamie wrote:


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.


No, you'd need a COUPLING capacitor.

Graham

Ignorant sap sucker.

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


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Michael Black]

(mrdarrett@gmail.com) writes:

I've noticed some audio amplifiers, like this one, need +/- 35VDC:
http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to ground:
http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/- power,
and the other is happy with 0-X power?

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the available
speaker movement range?

Michael

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

 

[Eeyore]

Jamie wrote:

Eeyore wrote:
Jamie wrote:

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.

No, you'd need a COUPLING capacitor.


Ignorant sap sucker.

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

I think it's time you went back to school.
http://en.wikipedia.org/wiki/Capacitive_coupling

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

Graham

 

[Don Bowey]

On 9/25/07 5:48 PM, in article BMhKi.70$n96.62@newsfe06.lga, "Jamie"
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Eeyore wrote:


Jamie wrote:


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.


No, you'd need a COUPLING capacitor.

Graham

Ignorant sap sucker.

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

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.

 

[Jamie]

Eeyore wrote:

Jamie wrote:


Eeyore wrote:

Jamie wrote:


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.

No, you'd need a COUPLING capacitor.


Ignorant sap sucker.

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


I think it's time you went back to school.
http://en.wikipedia.org/wiki/Capacitive_coupling

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

Graham

Oh boy, you're turning me on! keep coming!

I can tell you're nothing but a text book proclaimed
idiot.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Jamie]

Don Bowey wrote:

On 9/25/07 5:48 PM, in article BMhKi.70$n96.62@newsfe06.lga, "Jamie"
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Eeyore wrote:


Jamie wrote:



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.


No, you'd need a COUPLING capacitor.

Graham


Ignorant sap sucker.

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



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.






--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Eeyore]

Jamie wrote:

Don Bowey wrote:
"Jamie" wrote:
Eeyore wrote:
Jamie wrote:

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.


No, you'd need a COUPLING capacitor.


Ignorant sap sucker.

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


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.

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.

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.

Utterly WRONG.

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

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.

You are the most monumental moronic fuckwit.

" 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. "
http://en.wikipedia.org/wiki/Decoupling#Electronics


Graham

 

[Jamie]

Eeyore wrote:

Jamie wrote:


Don Bowey wrote:

"Jamie" wrote:

Eeyore wrote:

Jamie wrote:


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.


No, you'd need a COUPLING capacitor.


Ignorant sap sucker.

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


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.


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.



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.


Utterly WRONG.

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



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.


You are the most monumental moronic fuckwit.

" 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. "
http://en.wikipedia.org/wiki/Decoupling#Electronics


Graham

Arm chair text book rookie!.

All show and no go!.

Don't feel alone, I work with them
quite often. All living in their ideal
world!
There are many very smart and talented
people in this group that I say deserves a lot
more gratitude than what they get. You how ever, aren't
one of them.

Now go count your marbles and go to bed. Let some one
else use the community computer.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Don Bowey]

On 9/26/07 7:14 PM, in article e6EKi.61$M31.47@newsfe06.lga, "Jamie"
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Eeyore wrote:


Jamie wrote:


Don Bowey wrote:

"Jamie" wrote:

Eeyore wrote:

Jamie wrote:


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.


No, you'd need a COUPLING capacitor.


Ignorant sap sucker.

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


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.


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.



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.


Utterly WRONG.

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



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.


You are the most monumental moronic fuckwit.

" 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. "
http://en.wikipedia.org/wiki/Decoupling#Electronics


Graham

Arm chair text book rookie!.

All show and no go!.

Don't feel alone, I work with them
quite often. All living in their ideal
world!
There are many very smart and talented
people in this group that I say deserves a lot
more gratitude than what they get.

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

You how ever, aren't one of them.

Now go count your marbles and go to bed. Let some one
else use the community computer.

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

 

Arm chair text book rookie!.

All show and no go!.

Don't feel alone, I work with them
quite often. All living in their ideal
world!
There are many very smart and talented
people in this group that I say deserves a lot
more gratitude than what they get. You how ever, aren't
one of them.

Now go count your marbles and go to bed. Let some one
else use the community computer.

--
"I'm never wrong, once i thought i was, but was mistaken"

Not only are you wrong, you're also rude and poorly behaved. Graham
has it right. Of course that is what he does for a living so it is to
be expected.

GG

 

On Sep 25, 7:11 pm, et...@FreeNet.Carleton.CA (Michael Black) wrote:

(mrdarr...@gmail.com) writes:
I've noticed some audio amplifiers, like this one, need +/- 35VDC:
http://www.national.com/mpf/LM/LM3886.html

and some amplifiers are happy with 9 to 18VDC, with respect to ground:
http://focus.ti.com/lit/ds/symlink/tpa1517.pdf

Besides the obvious difference in power, how come one needs +/- power,
and the other is happy with 0-X power?

In the second case, for "no audio signal", is the speaker suspended
halfway between rest and max, resulting in only half of the available
speaker movement range?

Michael

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

It's making sense now!

Thanks everyone

Michael

 

[Rich Grise]

On Wed, 26 Sep 2007 02:11:12 +0000, Michael Black wrote:

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---

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

 

[Jamie]

stratus46@yahoo.com wrote:

Arm chair text book rookie!.

All show and no go!.

Don't feel alone, I work with them
quite often. All living in their ideal
world!
There are many very smart and talented
people in this group that I say deserves a lot
more gratitude than what they get. You how ever, aren't
one of them.

Now go count your marbles and go to bed. Let some one
else use the community computer.

--
"I'm never wrong, once i thought i was, but was mistaken"


Not only are you wrong, you're also rude and poorly behaved. Graham
has it right. Of course that is what he does for a living so it is to
be expected.

GG

And what do you think I do?

I can only expect an ignorant answer only because;

1. You don't know me.

2. And I really don't think you know Graham? or Mr. HAM.

How ever, if you watch the treads pass by like I have for several
months before I voiced my opinions. I have come to learn
who is and who isn't worthy of respect.

Before giving out your ignoramus views. Maybe you should be
more in touched with reality.

And don't bother asking what I do, neither you or any one
else gives a shit what you or I do for a living. All that
really matters here is, I can see it coming a mile away. And
what i'm seeing, isn't impressing me at all.






--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

[Don Bowey]

On 9/27/07 3:40 PM, in article f4WKi.110$Ga7.93@newsfe06.lga, "Jamie"
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

stratus46@yahoo.com wrote:

Arm chair text book rookie!.

All show and no go!.

Don't feel alone, I work with them
quite often. All living in their ideal
world!
There are many very smart and talented
people in this group that I say deserves a lot
more gratitude than what they get. You how ever, aren't
one of them.

Now go count your marbles and go to bed. Let some one
else use the community computer.

--
"I'm never wrong, once i thought i was, but was mistaken"


Not only are you wrong, you're also rude and poorly behaved. Graham
has it right. Of course that is what he does for a living so it is to
be expected.

GG

And what do you think I do?

What you do is make errors and then argue about it when someone points it
out. Do you get paid for that?

You really should be quiet and let this pass, as there is no way you can
show that you are correct.

I can only expect an ignorant answer only because;

1. You don't know me.

I know you enough to know that you make errors and then argue about it when
someone points it out.

2. And I really don't think you know Graham? or Mr. HAM.

Only too well, but so what?

How ever, if you watch the treads pass by like I have for several
months before I voiced my opinions. I have come to learn
who is and who isn't worthy of respect.

Your error indicates that this may not be valid.

Before giving out your ignoramus views. Maybe you should be
more in touched with reality.

Please take your own advice.

(snip)