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Single Ended vs Push Pull tube amplifiers

Discuss Single Ended vs Push Pull tube amplifiers at the Amplifiers within the HiFiVision.com - Audio Video Hi-Fi Forum; I found this really good explanation of push pull vs single ended tube amplifiers while ...

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Old 19th March 2012, 06:55 PM
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Smile Single Ended vs Push Pull tube amplifiers


I found this really good explanation of push pull vs single ended tube amplifiers while searching to learn about them.

Quote:
Think of PP as two men in a small boat, with one rowing
on each side. One rows while the other removes his
paddle from the water and moves it forward to row
again. This motion is repeated back and forth in alternating cycles. Though one is rowing on the starboard side
and one on the port side, the sum of their rowing actions
is a straight motion. Each expends only half the energy
required to propel the boat at a given speed. You can
liken SE to only one man in the same boat. He alone not
only has to muster the same rowing energy that two men
did together, but he must use a lot of his energy in turning his torso from side to side as he rows on each side of
the boat in order to make it go straight, wasted energy
that does not profit in making the boat move. It is wasteful and inefficient compared to two men rowing together, and the one man is simply not capable of expending the same level of energy as the two men combined are capable of
http://homepage.mac.com/tlinespeaker...v-PP-Part1.pdf
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Old 19th March 2012, 07:17 PM
 
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Re: Single Ended vs Push Pull tube amplifiers

That analogy is just so wrong. Yes push pulls obviously are more efficient since each tube is only amplifying half the signal and hence a pair of tubes can have higher power output.

However since no two tubes are exactly the same, there's always a problem of the both halves not being amplified exactly the same way. Normally there's always some overshoot/undershoot and added distortion. Also an ideal push pull will cancel out all 2nd order distortion. In reality a very small amount of 2nd order distortion remains. The majority of push pull distortion will be 3rd order which makes push pull tube amps sound quite like solid state designs. As a result they sound very very different compared to single ended designs which use a single tube to amplify the entire signal.

Also normally PPs operate in AB while SETs operate in A. Again personal preferences matter more than which one is a better amplifier.
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Old 19th March 2012, 07:29 PM
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Re: Single Ended vs Push Pull tube amplifiers

I got a nice AB of SET and Push pull couple of years back when at Rajivs place I heard the Lyrita SET and Cayin Push pull(iirc) back to back.
The SET had more lush vocals for sure while the Cayin had the upper hand when it came to percussion.

If at all efficiency was the main concern, I am sure there are other types of amps which do better on that count. But you go for a Toob amp because nothing else will do!
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Old 19th March 2012, 07:39 PM
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Re: Single Ended vs Push Pull tube amplifiers

Quote:
Originally Posted by reignofchaos View Post

Also normally PPs operate in AB while SETs operate in A. Again personal preferences matter more than which one is a better amplifier.
Don't forget the operation of push-pull when biased in class-A mode. Both devices[tubes/transistors/mosfets] are biased at 0.5 times the output load current in that case, whereas single ended has to conduct full load current as quiescent current. In this way both devices in Class-A push pull play their role at same time in load current.
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Old 19th March 2012, 07:56 PM
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Re: Single Ended vs Push Pull tube amplifiers

Quote:
Originally Posted by reignofchaos View Post
That analogy is just so wrong. Yes push pulls obviously are more efficient since each tube is only amplifying half the signal and hence a pair of tubes can have higher power output.

However since no two tubes are exactly the same, there's always a problem of the both halves not being amplified exactly the same way. Normally there's always some overshoot/undershoot and added distortion. Also an ideal push pull will cancel out all 2nd order distortion. In reality a very small amount of 2nd order distortion remains. The majority of push pull distortion will be 3rd order which makes push pull tube amps sound quite like solid state designs. As a result they sound very very different compared to single ended designs which use a single tube to amplify the entire signal.

Also normally PPs operate in AB while SETs operate in A. Again personal preferences matter more than which one is a better amplifier.
I wouldn't say its wrong though, in-accurate perhaps but it's an analogy to help someone like me to get an idea of what the basic difference is. Opening the door to understand deeper concepts after it

Quote:
Originally Posted by iaudio View Post
I got a nice AB of SET and Push pull couple of years back when at Rajivs place I heard the Lyrita SET and Cayin Push pull(iirc) back to back.
The SET had more lush vocals for sure while the Cayin had the upper hand when it came to percussion.

If at all efficiency was the main concern, I am sure there are other types of amps which do better on that count. But you go for a Toob amp because nothing else will do!
Hmm whats the life like for set and pp amps?

Quote:
Originally Posted by Kanwar View Post
Don't forget the operation of push-pull when biased in class-A mode. Both devices[tubes/transistors/mosfets] are biased at 0.5 times the output load current in that case, whereas single ended has to conduct full load current as quiescent current. In this way both devices in Class-A push pull play their role at same time in load current.
Went over my head hehe
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Old 19th March 2012, 07:59 PM
 
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Re: Single Ended vs Push Pull tube amplifiers

Quote:
Originally Posted by Kanwar View Post
Don't forget the operation of push-pull when biased in class-A mode. Both devices[tubes/transistors/mosfets] are biased at 0.5 times the output load current in that case, whereas single ended has to conduct full load current as quiescent current. In this way both devices in Class-A push pull play their role at same time in load current.
True and this is pretty common for bipolars/mosfets. Not so common for tubes.
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Old 19th March 2012, 08:27 PM
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That seems like a nice article from a brief cursory glance have bookmarked it for further reading. Enjoy your tube learning journey!


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Old 19th March 2012, 10:06 PM
 
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Re: Single Ended vs Push Pull tube amplifiers

There is something magical about SET amps when they are on song. Frequently, getting them to sing is a different matter altogether. In many cases they merely sound midrangey and dare I say strident. A SET amp needs to be paired with some sort of front horn to get the magic out.

My experience with a Wright 2A3 SET was very disappointing to begin with. Strident and midrangey with Klipsch Reference bookshelfs. After putting a Behringer DEQ2496 in the mix, different story altogether. Crystalline transparency, inner bloom, extended highs, the music has a palpable sweetness to it with those very same bookshelfs that were sounding so ordinary before.

I still have an Almarro A205A SEP - same story to begin with as the 2A3. Strident and midrangey. Updgraded the coupling caps to PIO but didnt make such a huge difference. This amp sounds fantastic at very low volume and when you are sitting 3-4 feet from the speakers, increase the volume and it would shriek. Then I connect these to the Lowthers in TP1 front horns and the resolution is simply stunning - the music just soars.

Then I have had the Dared 6L6 amps which are push pull for years now. They dont do anything much wrong, they have decent low end, clean midrange and decent highs - but they do not do anything exceptionally well either. They do not have the magic. I do not think they can ever do the crystalline transparency thing that a SET can do with a little effort. I have stuck with these the longest because they are the least fussy and sound good with various genres of music. It is entirely possible I have heard the best a SET amp can do whereas I have yet to hear a really good PP amp. I am sure there are some really good PP amps out there that could give a SET a run for its money.
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Old 28th March 2012, 01:11 AM
 
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Re: Single Ended vs Push Pull tube amplifiers

In my misspent youth I worked in a custom shop trimming the output stage of push-pull guitar amplifiers. Every tube had slight differences, and changing components allowed one to get high efficiency and lower distortion. This was at a time when commercial tubes were made in million piece quantities. This caught the attention of the glass makers and special borosilicate glass was available in the T sizes required by vacuum tubes. The cathode makers were on their best game, and the heater manufacturers were turning out very long life units.

The problem today is the glass is crap. I still use tubes in image systems, and the glass is the same as used for making light bulbs. No one can place a million dollar order to make the glass like they used to, and the chemicals involved are banned in most of the world. The number one problem is awful cathodes and carbon migration through the glass. Tube manufactures also have trouble making a decent glass seal, and oxygen sneaks in along the pins at the metal to glass seal. You could keep the tubes heated, as that expels the oxygen but that bakes the cathodes.

My solution is to use solid state amps, and let a dsp mimic the rich warm distortion of tubes.
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Old 28th March 2012, 09:30 AM
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Re: Single Ended vs Push Pull tube amplifiers

That's akin to throwing the baby out with the bathwater!

If DSPs could mimic the sound of tubes, guitar tube amplifiers would have disappeared long ago. That they haven't, that they are responsible for the continued production of tubes, speaks for itself.

May I suggest a simple reason for the preferred sound of SET tube amps - simple circuits!In such a tube power amplifier there are often just two amplification stages per channel - that's two amplifying devices, with no global feedback. In contrast, solid state amplifiers have upto 10 devices, and usually employ global feedback (Pass's designs are an exception). The less circuitry that an audio signal sees, the less the chances of degradation. Simple circuits, implemented well, always sound better!

Viren


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