low-power audio amp basics

May 22, 2014

For some low-power audio amps, usually less than 2 Watts, I see the amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at 1/2 V during the silent parts, to allow the speaker room to move during the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Thanks,

Michael

May 22, 2014

On Thursday, May 22, 2014 1:52:09 PM UTC-7, Ian Field wrote:

mrdarrett@gmail.com> wrote in message

news:d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com...

For some low-power audio amps, usually less than 2 Watts, I see the

amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply

required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at

1/2 V during the silent parts, to allow the speaker room to move during

the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Normally with single ended supplies, you'd couple the speaker with a DC

blocking capacitor - big electrolytic, possibly expensive.

Will it also consume more power during fairly quiet music passages than a split supply?

An alternative is to use 2 identical amplifiers in BTL (bridge tied load) -

you drive the 2 amplifiers with opposite phase inputs and hang the speaker

between the 2 outputs.

If you Google "BTL amplifier" you should get enough hits to explain it

fully.

Oh ok! Is this how it's commonly done with car audio?

If you want decent power from a low-ish single rail, there's various off the

shelf BTL amp chips - one of my favourites is the TDA7052, there is a

suffixed version with DC volume control.

Thanks!

Michael

Jim Thompson · May 23, 2014

On Thu, 22 May 2014 10:28:44 -0700 (PDT), mrdarrett@gmail.com wrote:

For some low-power audio amps, usually less than 2 Watts, I see the amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at 1/2 V during the silent parts,

Yes

>to allow the speaker room to move during the parts when the input signal is negative?

It's to provide amplifier headroom. With a single supply, the speaker
is capacitively coupled to the amplifier output.

Is the +/- supply more efficient for this reason?

Thanks,

Michael

May 23, 2014

On Thursday, May 22, 2014 3:42:44 PM UTC-7, Maynard A. Philbrook Jr. wrote:

In article <d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com>,

mrdarrett@gmail.com says...

For some low-power audio amps, usually less than 2 Watts, I see the amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at 1/2 V during the silent parts, to allow the speaker room to move during the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Thanks,

Michael

With a bipolar supply (+&- to COM), you get twice the swing and

no need for a DC blocking cap which allows you to output down to

0 HZ. (DC)

Jamie

So, even a +6V - 0 - (-6V) supply should be better than +12V-0, right?

Thanks,

Michael

Ian Field · May 23, 2014

<mrdarrett@gmail.com> wrote in message
news:d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com...

For some low-power audio amps, usually less than 2 Watts, I see the
amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply
required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at
1/2 V during the silent parts, to allow the speaker room to move during
the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Normally with single ended supplies, you'd couple the speaker with a DC
blocking capacitor - big electrolytic, possibly expensive.

An alternative is to use 2 identical amplifiers in BTL (bridge tied load) -
you drive the 2 amplifiers with opposite phase inputs and hang the speaker
between the 2 outputs.

If you Google "BTL amplifier" you should get enough hits to explain it
fully.

If you want decent power from a low-ish single rail, there's various off the
shelf BTL amp chips - one of my favourites is the TDA7052, there is a
suffixed version with DC volume control.

May 23, 2014

On Thursday, May 22, 2014 5:06:48 PM UTC-7, Phil Allison wrote:

mrdarrett@gmail.com

For some low-power audio amps, usually less than 2 Watts,

I see the amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/-

power supply required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide

a voltage at 1/2 V during the silent parts, to allow the speaker

room to move during the parts when the input signal is negative?

** The electro cap in series with the speaker charges up to half supply

voltage at switch on - removing DC from the speaker and then holds that

voltage during operation. Current can flow into the speaker from the

amplifier in both directions, just as it would with a split supply design.

Is the +/- supply more efficient for this reason?

** Nope.

Single rail amps have a big advantage when the supply voltage has to be

regulated or is derived from a battery. Also, it eliminates the possibility

of DC flowing into the speaker because of a fault in the amp.

.... Phil

Ok! Thanks for the clarification!

Michael

May 23, 2014

On Thursday, May 22, 2014 4:39:51 PM UTC-7, Maynard A. Philbrook Jr. wrote:

In article <f1875493-67e1-4078-b800-04bdd4019d82@googlegroups.com>,

mrdarrett@gmail.com says...

Jamie

So, even a +6V - 0 - (-6V) supply should be better than +12V-0, right?

Thanks,

Michael

In a case like that, you would get the same results on the

swing level if you were to us a capacitor decoupled type over

a DC coupled type.

However, using no capacitor is still better because it removes

a component from the circuit that could hamper the flat response

output, in other words, the capacitor is not going to be the same

Z (impedance) across the frequency spectrum.

Jamie

Ooh. Ok!

Maynard A. Philbrook Jr. · May 23, 2014

In article <d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com>,
mrdarrett@gmail.com says...

For some low-power audio amps, usually less than 2 Watts, I see the amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at 1/2 V during the silent parts, to allow the speaker room to move during the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Thanks,

Michael

With a bipolar supply (+&- to COM), you get twice the swing and
no need for a DC blocking cap which allows you to output down to
0 HZ. (DC)

Jamie

Maynard A. Philbrook Jr. · May 23, 2014

In article <f1875493-67e1-4078-b800-04bdd4019d82@googlegroups.com>,
mrdarrett@gmail.com says...

Jamie

So, even a +6V - 0 - (-6V) supply should be better than +12V-0, right?

Thanks,

Michael

In a case like that, you would get the same results on the
swing level if you were to us a capacitor decoupled type over
a DC coupled type.

However, using no capacitor is still better because it removes
a component from the circuit that could hamper the flat response
output, in other words, the capacitor is not going to be the same
Z (impedance) across the frequency spectrum.

Jamie

Phil Allison · May 23, 2014

<mrdarrett@gmail.com>

For some low-power audio amps, usually less than 2 Watts,
I see the amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/-
power supply required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide
a voltage at 1/2 V during the silent parts, to allow the speaker
room to move during the parts when the input signal is negative?

** The electro cap in series with the speaker charges up to half supply
voltage at switch on - removing DC from the speaker and then holds that
voltage during operation. Current can flow into the speaker from the
amplifier in both directions, just as it would with a split supply design.

> Is the +/- supply more efficient for this reason?

** Nope.

Single rail amps have a big advantage when the supply voltage has to be
regulated or is derived from a battery. Also, it eliminates the possibility
of DC flowing into the speaker because of a fault in the amp.

..... Phil

Bob Masta · May 23, 2014

On Thu, 22 May 2014 21:52:09 +0100, "Ian Field"
<gangprobing.alien@ntlworld.com> wrote:

mrdarrett@gmail.com> wrote in message
news:d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com...
For some low-power audio amps, usually less than 2 Watts, I see the
amplifier powered by +V and ground:
http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply
required.
http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage at
1/2 V during the silent parts, to allow the speaker room to move during
the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Normally with single ended supplies, you'd couple the speaker with a DC
blocking capacitor - big electrolytic, possibly expensive.

An alternative is to use 2 identical amplifiers in BTL (bridge tied load) -
you drive the 2 amplifiers with opposite phase inputs and hang the speaker
between the 2 outputs.

If you Google "BTL amplifier" you should get enough hits to explain it
fully.

If you want decent power from a low-ish single rail, there's various off the
shelf BTL amp chips - one of my favourites is the TDA7052, there is a
suffixed version with DC volume control.

Note that with a bridge configuration you are effectively
doubling the voltage swing, which quadruples the available
power output. This is especially useful in systems (like
autos) with low voltage supplies.

Best regards,

Bob Masta

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Science with your sound card!

Ian Field · May 23, 2014

<mrdarrett@gmail.com> wrote in message
news:57197402-c253-48d7-8538-444751e92d9d@googlegroups.com...

On Thursday, May 22, 2014 1:52:09 PM UTC-7, Ian Field wrote:
mrdarrett@gmail.com> wrote in message

news:d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com...

For some low-power audio amps, usually less than 2 Watts, I see the

amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply

required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage
at

1/2 V during the silent parts, to allow the speaker room to move during

the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Normally with single ended supplies, you'd couple the speaker with a DC

blocking capacitor - big electrolytic, possibly expensive.

Will it also consume more power during fairly quiet music passages than a
split supply?

An alternative is to use 2 identical amplifiers in BTL (bridge tied
load) -

you drive the 2 amplifiers with opposite phase inputs and hang the
speaker

between the 2 outputs.

If you Google "BTL amplifier" you should get enough hits to explain it

fully.

Oh ok! Is this how it's commonly done with car audio?

As for quiescent current - it depends how well the 2 amplifiers are
matched/biassed, one or two of the 7052 chips I've used weren't all that
good.

Bridge amplifiers are pretty common in cars, but the real in car audio
fanatics buy bloody great inverters that produce split rails of up to 56V
each - and kill the ignition at high volume if the alternator isn't running
at max output!

Philips made a chip that also drives a charge pump voltage booster from the
regular output, internal circuitry detects the onset of clipping and
activates an extra pair of transistors that run off the capacitors charged
by the charge pump - no doubt other manufacturers have copied the idea by
now.

Ian Field · May 23, 2014

<mrdarrett@gmail.com> wrote in message
news:f1875493-67e1-4078-b800-04bdd4019d82@googlegroups.com...

On Thursday, May 22, 2014 3:42:44 PM UTC-7, Maynard A. Philbrook Jr.
wrote:
In article <d5af57ec-b30c-4231-9e99-e4f838553cce@googlegroups.com>,

mrdarrett@gmail.com says...

For some low-power audio amps, usually less than 2 Watts, I see the
amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/- power supply
required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide a voltage
at 1/2 V during the silent parts, to allow the speaker room to move
during the parts when the input signal is negative?

Is the +/- supply more efficient for this reason?

Thanks,

Michael

With a bipolar supply (+&- to COM), you get twice the swing and

no need for a DC blocking cap which allows you to output down to

0 HZ. (DC)

Jamie

So, even a +6V - 0 - (-6V) supply should be better than +12V-0, right?

On one occasion I found a TDA7052 BTL amp running from the +5V rail on an
Olivetti laptop board.

Ian Field · May 23, 2014

<mrdarrett@gmail.com> wrote in message
news:d2b15b78-b8c7-441e-87ce-7fbbad0a3077@googlegroups.com...

On Thursday, May 22, 2014 5:06:48 PM UTC-7, Phil Allison wrote:
mrdarrett@gmail.com

For some low-power audio amps, usually less than 2 Watts,

I see the amplifier powered by +V and ground:

http://www.redcircuits.com/Page33.htm

For other, usually higher-powered amplifiers, I see a +/-

power supply required.

http://www.redcircuits.com/Page164.htm

Do the amplifiers without a +/- supply continuously provide

a voltage at 1/2 V during the silent parts, to allow the speaker

room to move during the parts when the input signal is negative?

** The electro cap in series with the speaker charges up to half supply

voltage at switch on - removing DC from the speaker and then holds that

voltage during operation. Current can flow into the speaker from the

amplifier in both directions, just as it would with a split supply
design.

Is the +/- supply more efficient for this reason?

** Nope.

Single rail amps have a big advantage when the supply voltage has to be

regulated or is derived from a battery. Also, it eliminates the
possibility

of DC flowing into the speaker because of a fault in the amp.

.... Phil

Ok! Thanks for the clarification!

He makes a good point about a fault causing DC current through the speaker -
any decent split rail amp will have a protection circuit and relays to
isolate the load if it detects a fault.

Maynard A. Philbrook Jr. · May 24, 2014

In article <xOKfv.131164$B%3.93498@fx23.am4>,
gangprobing.alien@ntlworld.com says...

Ok! Thanks for the clarification!

He makes a good point about a fault causing DC current through the speaker -
any decent split rail amp will have a protection circuit and relays to
isolate the load if it detects a fault.

It would be a piss poor design if a bridge or DC output amp
didn't initiate silently.

Jamie

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