Class-G Audio Amplifiers

Even though we publish new blogs daily from your intrepid editor and from a number of well-known writers, sometimes it's good to have a look back at some of our articles from the recent past that were well received.

Audio seems to be a popular topic among engineers. Here is one that discusses class-G audio power amplifiers. Class-G amplifiers share some traits with the more well-known class-D amplifiers — notably, better power efficiency. Better efficiency makes them ideal for battery operated portable devices. They provide this efficiency while maintaining high levels of performance.

This article is in two parts. Part 1 looks at the general details of different classes of amplifiers and compares their performance. Then it moves into the specific details of how class-G works.

Part 2 gets into the class-G performance specifics.

(Source: Texas Instruments)

(Source: Texas Instruments)

(Source: Texas Instruments)

(Source: Texas Instruments)

Let us know about your experiences working with audio in general and these newer classes of amplifiers in particular.

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7 comments on “Class-G Audio Amplifiers

  1. David Maciel Silva
    May 31, 2013

    Hi Brad,

    In the past I used a class B amplifier, the TDA1518 Phlips, good cost is a good power output.

    It was a simple, one amp audio for gaming equipment, in every way to achieve maximum power had a distortion signal too big, anyway, it was good but we needed to solve some small details HW, especially with the power power, which was to be linear with a loud noise.

    Another point that was already waiting for something to arrive at the maximum the integrated heated too much, then a good aréa dissipation was created.

    There was something with a content tencnológio very large, but in the end application had an excellent result, I must stress the small details given above.

    Another very good experience now with energized circuit voltage lower typical 3v, this is the ISD4002 is a ci for recording audio, a few seconds, lol enough to let me say “bald” … I had many problems with the filters and the loss of the messages that were in memory of the uC, anyway after a good fight could improve perfomace, the output signal was white, no noise, it worked well …

    Until …. the internal battery is discharged, as there was limited output signal so that the consumer was less …

    Finally after much beating unable to handle the situation detection system using a low battery power and limit the ISD …

    I learned a lot, but got …

  2. amrutah
    June 4, 2013

    Thanks for sharing this Brad.

      The Class-G are surely helpful in reducing the power.  The programming of the supply power according to the audio peak is very helpful.

      As shown in Fig 2 above the supply is ramped up and down immediately, will it not introduce any click and pop noise?

      The DC-DC will be switching and switching at frequency higher, say 10 times the audio range. Does this noise get filtered out by the speaker inductances?

  3. amrutah
    June 4, 2013

    Does Class-G architecture hold good for different speaker loads?

    Does having Class-G architecture good only for lower loads, since current is a function of voltage ratio (VBAT/VSUP)?

  4. eafpres
    June 4, 2013

    When you start talking audio, when you get to guitar amplifiers, you immediately get to the tube vs. SS questions.  There are still lots of Class A and AB guitar amps sold based on tubes in some sections, like the preamp.

    A couple of years ago I started hearing there was a solid state device that had been engineered to match the characteristics of 12AX7 tubes.  I saw some articles saying a company was producing limited quantities.  I even found a picture of one:

    12AX7 solid state drop in replacement

    Any comments on the ever-lasting tubes vs. SS in power amps like guitar amps?  Has anyone seen or used one of these alleged replacements?

  5. Brad Albing
    June 4, 2013

    @eafpres – looks like s/o made a few of those in the basement (or garage) – does not inspire confidence.

  6. Brad Albing
    June 24, 2013

    @amrutah – no – the ramping of the supply voltage will not pass thru to the speaker – as long as it has a little bit of actual ramp time. Any good amplifier is designed to have pretty good power supply rejection ration (PSRR), so if the supply doesn't ramp too quickly, the dv/dt won't pass thru. Also, switching noise is sufficiently high so that it won't show up at the speaker.

  7. Brad Albing
    June 24, 2013

    @amrutah – it would be appropriate for and work well with various speaker load impedances.

    Note that for high impedance loads, you may not realize much overall power savings.

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