Forums

low-power audio amp basics

Started by Unknown 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
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
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<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.
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
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
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
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
<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
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
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!