Can someone explain push pull power amp"

Re: Can someone explain push pull power amp"

Sound travels in waves that go up and down.

A Class A push amp will amplify the entire wave, the positive and the negative of the wave.

A Class AB push/pull amp has two amps, one to handle the positive half of the wave, and another to handle the negative half of the wave.

Class AB is more efficient because two amps handle the load, which allows them to be higher power ratings and output.

Class A is regarded as better sounding or having better fidelity, but the amp is working very hard, they can't handle high power and can have a shorter lifespan.

The trade off is the possibility of 'crossover distortion' or a smearing or lack of fidelity as the sound wave crosses from positive to negative and switches from one amp to the other.

Other explanations/opinons may vary.
 
Re: Can someone explain push pull power amp"

A really rough explanation is it's a type of power amp that takes a sort of positive and negative half of the sound being amplified and half the power tubes amplify one phase of the soundwave and the other half the tubes amplify the other half. They are added back together in the transformer.

In common guitar amps it's made so that each power tube or section of power tubes doesn't have to amplify all the sound all of the time. Sometimes half the power tubes are amplifying one side of the signal (mostly) and the other side gets to rest a tiny bit, saving tube life and lowering the temperature. Also some noise made by the amp circuitry is canceled out when the two halves of the signal are recombined in the transformer.

So more tube life, less noise in a push pull, generally, and the tubes run more efficiently allowing the design to push more watts to the speaker. Downside possibly is that along with noise, some harmonics (so-called even order harmonics) of the guitar signal are also canceled out leaving a stronger fundamental tone and less of what you'd call distortion.

In contrast are "single ended" amplifiers, where the output tube (most often one esp. in guitar amps, sometimes more I think) is always amplifying the whole signal. The harmonic i was just mentioning (the 2nd order harmonic, even numbered harmonics especially the 2nd one sounding very musical) doesn't get canceled. But the tube runs hot and wastes a lot of energy as heat cuz it's on all the time.
So single ended amps run hot, burn up tubes faster, but sound a little different, IMO slightly richer, but also slightly noisier.

TL;DR: push pull=higher wattage, more tubes, less distortion, cooler tubes, longer tube life. single ended=lower wattage, usually one tube, tubes run hot, tubes burn out faster, more noise but you get more of the good kind of distortion.
Cuz there's a lot more to amp design than the type of power amp, it in reality doesn't tell you much about what to expect from the amp but most single ended amps I've played do sound a touch more "immediate" and "alive" but can also sound too overdriven when dimed, kinda mushy and blurry.
 
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Re: Can someone explain push pull power amp"

Sounds good to me. (I'll save the discussion of biasing schemes for another time.) Push-pull amps can usually drive more difficult loads and have more authority in the bass. Single-ended Class A amps are sometimes described as having finer "inner detail". Personally, I would love to try one for my bedroom-volume blooze noodlings. But if you want to rock out at volume, push-pull is the way to go.
 
Re: Can someone explain push pull power amp"

So essentially at bedroom volumes I'd lose a little tonally but can push more power and distort more easily with a push pull?
 
Re: Can someone explain push pull power amp"

At bedroom volumes no tube amp's power section is generating appreciable distortion. And it is true most tube amps don't sound their best at bedroom volumes but many still sound pretty damn good. Understanding amplifier classes is nice but there are so many other factors that contribute to a final sound.
 
Re: Can someone explain push pull power amp"

I've heard it said by amp techs that Vox AC30's even though labeled as "Class A" amplifiers are not really true Class A due to how the amp is designed and run, and that the AC30 straddles the Class A and Class A/B operation at times.

Class A amps are "always on" and conduct for the full 360 degrees of signal. In Class A/B one pair of output tubes conducts + 180 degrees of signal (push) while the other pair of output tubes conducts the other half of the - 180 degree signal (pull).
 
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Re: Can someone explain push pull power amp"

TNTales said:
So essentially at bedroom volumes I'd lose a little tonally but can push more power and distort more easily with a push pull?
Click to expand...

Not really, generally AB or push-pull amps have more power than class A amps. That said, since you are specifically asking about the BlackStar HT-5, it uses a 12BH7 tube, which is a dual triode preamp tube. They are using the 2 sides of that tube as a low power push pull power section, it's actually pretty clever. So, being a low power amp, you can push it harder to get some tube breakup in the power section, but even at 5W, that can still be pretty loud.
 
Re: Can someone explain push pull power amp"

Keep in mind that an amplifier does not need to be single ended (one tube) to be considered "class A" and that class A push/pull amplifiers exist. The main definition of "class A" is that the output stage is biased so that the output devices conduct through all 360 degrees of the wave. In a class A push pull, one side is designed to favor the positive side, and the other the negative side, but both sides conduct the entire wave form at all times. What this means is that "class A" is not a design so much as it's a mode of operation. In other words, a single tube amp MUST be class A, but one or two or more evenly matched pairs of tubes can be operated in class A mode.

Southbound Suarez said:
In Class A/B one pair of output tubes amplifies + 180 degrees of signal (push) while the other pair of output tubes amplifies the other half of the - 180 degree signal (pull).
Click to expand...


In a class B amp, the tubes do exactly 180 degrees of the signal. In an AB amp, the designer sets it so that the tubes conduct a bit beyond 180 degrees, say 190, and this makes it get some of the characteristics of the class A operation, and some of the B in one amp.

The reason, besides efficiency, that class AB was created was so that the amp designer could the minimize crossover distortion of class B, as well as retaining distortion characteristics...while also lowering them...of the class A design (even order harmonics). Most all of the amplifiers designed back then were made to minimize distortion of any kind. It took Jim Marshall, and Randall Smith to finally make the amp designer world embrace distortion as an end unto itself.

Here's a description that's better than I could come up with.

http://www.audioholics.com/audio-amplifier/amplifier-classes

"As compared with the other amplifier classes we’ll cover, Class A amps are relatively simple devices. The defining principle of Class A operation is that all of an amplifier’s output devices must be conducting through the full 360 degree cycle of a waveform. Class A can also be broken down into single ended and push/pull amplifiers. Push/pull diverges from the basic explanation above by utilizing output devices in pairs. While both devices are conducting through the full 360 degree cycle, one device will shoulder more of the load during the positive portion of the cycle, while the other handles more of the negative cycle; the primary advantage of this arrangement is reduced distortion relative to single ended designs, as even order harmonics are cancelled out. In addition, push/pull Class A designs are less susceptible to hum; single ended designs tend to require special attention to the power supply to mitigate this issue."
 
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Re: Can someone explain push pull power amp"

guitfiddle said:
Keep in mind that an amplifier does not need to be single ended (one tube) to be considered "class A" and that class A push/pull amplifiers exist. The main definition of "class A" is that the output stage is biased so that the output devices conduct through all 360 degrees of the wave. In a class A push pull, one side is designed to favor the positive side, and the other the negative side, but both sides conduct the entire wave form at all times. What this means is that "class A" is not a design so much as it's a mode of operation. In other words, a single tube amp MUST be class A, but one or two or more evenly matched pairs of tubes can be operated in class A mode.




In a class B amp, the tubes do exactly 180 degrees of the signal. In an AB amp, the designer sets it so that the tubes conduct a bit beyond 180 degrees, say 190, and this makes it get some of the characteristics of the class A operation, and some of the B in one amp.

The reason, besides efficiency, that class AB was created was so that the amp designer could the minimize crossover distortion of class B, as well as retaining distortion characteristics...while also lowering them...of the class A design (even order harmonics). Most all of the amplifiers designed back then were made to minimize distortion of any kind. It took Jim Marshall, and Randall Smith to finally make the amp designer world embrace distortion as an end unto itself.

Here's a description that's better than I could come up with.

http://www.audioholics.com/audio-amplifier/amplifier-classes

"As compared with the other amplifier classes we’ll cover, Class A amps are relatively simple devices. The defining principle of Class A operation is that all of an amplifier’s output devices must be conducting through the full 360 degree cycle of a waveform. Class A can also be broken down into single ended and push/pull amplifiers. Push/pull diverges from the basic explanation above by utilizing output devices in pairs. While both devices are conducting through the full 360 degree cycle, one device will shoulder more of the load during the positive portion of the cycle, while the other handles more of the negative cycle; the primary advantage of this arrangement is reduced distortion relative to single ended designs, as even order harmonics are cancelled out. In addition, push/pull Class A designs are less susceptible to hum; single ended designs tend to require special attention to the power supply to mitigate this issue."
Click to expand...

Leo Fender, and not Jim Marshall and Randall Smith. Leo was constantly at odds with his engineers who wanted to stabilize the output sections of his amps to make them more audiophile in nature, take f.e. the Fender "Ultra Linear Twin" after Leo's departure from Fender. As for some of the rest of your comments, I dare you to go on the Marshall Forum and relay what you have just posted here.
 
Re: Can someone explain push pull power amp"

Southbound Suarez said:
Leo Fender, and not Jim Marshall and Randall Smith. Leo was constantly at odds with his engineers who wanted to stabilize the output sections of his amps to make them more audiophile in nature, take f.e. the Fender "Ultra Linear Twin" after Leo's departure from Fender. As for some of the rest of your comments, I dare you to go on the Marshall Forum and relay what you have just posted here.
Click to expand...

Funny thing about facts is that they don't rely on the belief of guys on the Marshall forum to be true.
 
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Re: Can someone explain push pull power amp"

guitfiddle said:
Funny thing about facts is that they don't rely on the belief of guys on the Marshall forum to be true.
Click to expand...

Again I DARE YOU to relay what you said here on the Marshall Forum because there are quite a few established techs there that build and repair amps for a living so, before you state information "as fact" you'd better be correct because these guys will most assuredly call you out.
 
Re: Can someone explain push pull power amp"

Southbound Suarez said:
Again I DARE YOU to relay what you said here on the Marshall Forum because there are quite a few established techs there that build and repair amps for a living so, before you state information "as fact" you'd better be correct because these guys will most assuredly call you out.
Click to expand...

I'll take the word of the good folks at RCA over whatever the techs at the Marshall Forum have to say.:fing2:

From page 12 of an early revision of the RCA Tube Receiving Manual:

RCA%20TRM%20page%2012_zpstkebwkff.jpg
 
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