Single Ended vs Push Pull tube amplifiers

[corElement]

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

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 pro?t in making the boat move. It is wasteful and inef?cient 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/tlinespeakers/vaughn/downloads/SE-v-PP-Part1.pdf

 

[reignofchaos]

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.

 

[iaudio]

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!

 

[kanwar]

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.

 

[corElement]

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

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?

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

 

[reignofchaos]

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.

 

[stevieboy]

That seems like a nice article from a brief cursory glance have bookmarked it for further reading. Enjoy your tube learning journey!


Torque ain't cheap but it sure knocks yer socks off

 

[Beast_of_burden]

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.

 

[Moviela]

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.

 

[viren bakhshi]

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

 

[corElement]

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.

Hmm, I had totally forgotten about emissions, do they harm the environment the way way incandescent bulbs do?

 

[Thad E Ginathom]

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

As a boat lover, I'd say it is completely wrong, because people don't row boats like that. One person pulls on two oars together. Two people pull on one oar each together.

Maritime pedantry aside, as someone who doesn't understand how amplifiers work, yes, it gave me a useful mental picture

 

[alpha1]

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

Not really.
Current breed of digital processing is astonishingly close to the Valve Amps in producing the "tube" sound, ... and of course the flexibility of more sounds than just the tube sound.
(AxeFX2, Line6 HD etc)

If you give example of a professional artist using a Tube amp - he has got money and he makes a living making music - so he can afford to spend unlimited amount. (and he has got a particular sound in mind which is typical of an overdriven tube amp circuitry)

Why would he look for a replacement (digital processing) unless he is cash strapped?


This is the reason why Tube amps are still surviving in Guitar market.
Surprisingly, no other genre of musician actually prefers tube amps.
And what about the Live PA system? Solid state all the way.

 

[Beast_of_burden]

I personally think there is too much emphasis on tone when talking tubes. A good 2A3 set has an incredible amount of air, detail, sustain and harmonic sweetness that is really hard for DSP or a solid state amp to replicate. Dont get me wrong, I would be the first one to use a digital EQ such as the Behringer DE2496 with a very good SET amp. There is more to a SET amp than just the tone.

NOS tubes are great, no two ways about it and I speak from personal experience. But there a few good new production tubes as well. I have got great sound from Svetalana 2A3 tubes, I hear the Shuguang 2A3C is even better. The EH 6l6 are also good. Granted, new production tubes arent as long-lived but then they are quite cheap compared to NOS. New production tubes have been getting better but they are still a long way from good NOS tubes, but I hope they will get there in the not too distant future.

 

[corElement]

I wish I could afford a good high watt set amp. Maybe in a few years.

 

[anm]

you don't need high watt tube amp. You just need the right speakers. Harmony one + 2A3 for music.

 

[Beast_of_burden]

you don't need high watt tube amp. You just need the right speakers. Harmony one + 2A3 for music.

Absolutely, SET amp power is a given - low output but high quality watts. You need to get the right speakers - atleast 94db sensitivity. Any decent speaker from Klipsch would be great(have got great results with a Klipsch RB61). 2A3 amps are typically 3.5 watt per channel and they sound quite robust with a sensitive speaker such as the Klipsch even in the bass.

I would love to audition the Lyrita 2A3 in Bangalore if I could. Never heard a 300B, would love to audition that too if I could. I will be building the Tp1 front horns next month to go with my Almarro A205A SEP.

 

[kanwar]

Sometimes i wonder why there is no high power SET [Tube or Transistor] amplifier. :indifferent14:

 

[corElement]

There are, but they're very very expensive.

 

[kanwar]

And why they are expensive?