Push Pull vs. BTL.

Discussion in 'General Electronics Chat' started by superduper, May 18, 2011.

  1. superduper

    Thread Starter Active Member

    Dec 5, 2010
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    Is there a difference between a push/pull amplifier and a BTL (bridge tied load) configured amplifier?
     
  2. #12

    Expert

    Nov 30, 2010
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    The BTL is a form of push-pull, but it can inflict twice as much voltage on the load (given the same power supply voltages the push-pull amp has) because it has 2 pushers and 2 pullers.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    Because the BTL amplifier uses two amplifiers to make the output swing almost double the output swing of a single-ended push-pull amplifier its output current is also almost doubled, then its output power is almost 4 times as much.
    Actually it is about 3.5 times as much because the losses are also doubled.
     
  4. superduper

    Thread Starter Active Member

    Dec 5, 2010
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    So SE amps can also be push pull? I guess I'm trying to understand the technical differences and not the resulting power output results.
     
  5. #12

    Expert

    Nov 30, 2010
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    This is the first mention of a singel ended amplifier. It has nothing to do with push-pull.
     
  6. Audioguru

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    A single-ended amplifier is one amplifier that drives one wire of a speaker with the other wire of the speaker connected to ground.
    A BTL or bridged amplifier uses two amplifiers so that each wire of a speaker is driven (out of phase) so that the voltage across the speaker and therefore its current are almost doubled. Then the power in the speaker is almost quadrupled.

    Nearly all audio amplifiers are push-pull except a few odd class-A amplifiers.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Terminology has changed over the years. At one time a "single-ended" amplifier could have implied one using a single output electron tube (or two or more in parallel), as opposed to a push-pull amplifier using two tubes working in anti-phase, normally coupled to the load using a centre-tapped transformer.

    A single-ended audio power amplifier using the old-fashioned definition would have been class A, not class B. Otherwise, only part of the waveform would have been reproduced, causing profound distortion. These old-fashioned amplifiers were quite inefficient, but at the time when they were made low efficiencies were usual. This example device used more power to heat its cathode than ever made it to the loudspeaker. http://www.r-type.org/exhib/aad0112.htm

    Transistor audio power amplifiers of the primitive single-ended type were little used, apart from intermediate drivers in larger amplifiers, and some early transistorised automobile radios which used a single power transistor.

    Early transistor push-pull amplifiers used two similar devices feeding a tapped transformer like their tube counterparts, but later complementary devices in series across the power supply became usual. This led on to the possibility of the bridge-connected amplifier, so that a modern car stereo might have not one but at least eight output transistors (in an IC).

    Push-pull amplifiers can be biased variously from class B (relatively efficient but tends to be non-linear particularly at low levels) through class AB compromises which are the most usual choice to class A, which some people say is the best but is very wasteful of power.
     
  8. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Maybe this imagine will help
     
    • BTL.PNG
      BTL.PNG
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  9. Audioguru

    New Member

    Dec 20, 2007
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    The ST Micro and Philips datasheets disagree with you guys but agree with me:
     
  10. superduper

    Thread Starter Active Member

    Dec 5, 2010
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    The visual aid helps a lot but I see lots of IC amp modules advertised and described as SE. When doubled up like how audioguru says, with each leg of the speaker terminals driven by it's own amp in complementary phase, it is then described as BTL.

    So the image Jony130 contributed depicts SE and PP as clearly different designs. But then can the SE design also be "bridged" out of phase to create a BTL configuration or must the BTL amps always be PP?

    Or is BTL amps always PP but PP amps not necessarily BTL?
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    The low battery voltage in a car (13.6V) causes low power in a speaker when driven from an amplifier with a single output (a single-ended amplifier). Most older car amplifier ICs use class-AB in a push-pull circuit but newer amplifiers use class-D in a switching circuit.
    The output swing is about 11.5V into a 4 ohm speaker which produces only 4.1W.

    Many car amplifier ICs use a BTL design with a separate push-pull amplifier for each wire of a speaker. Their output swing is 22V and they produce 15.1W into a 4 ohm speaker.

    Jony's "SE" circuit is a class-A heater that is rarely used for an amplifier design.
    It is never used in a car amplifier because it wastes a lot of power making heat.
     
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