there is something about pp that is overlooked: the output and interstage transformers fall in and out of magnetisation at every zero-crossing of the signal (at every polarity change).
This is only correct if the amplifier is biased class B.
last comment about bass: this is tricky to comment on. Valve amps have feeble damping factors compared to SS, but is that a good or bad thing? It’s hard to give a definitive answer, and it’s more about the speakers and the room as to whether the ‘sloppy’ bass of valves sounds better than the ‘tight‘ Bass of SS, it can go either way, so keep minds open on that… my opinion is the low damping from tube amps works pretty well with closed box speakers, but that high damping factor is necessary to control reflex port behaviour. Not sure about dipoles though.
If the amplifier employs enough feedback it can behave as a voltage source and no worries with the bass. But I expect the amp you're describing here is zero feedback, in which case it will behave as a power source. That means the speaker has to be designed to expect the amp to have a higher output impedance associated with this behavior. There are a good number of speakers for which this is so- any speaker that works with an SET for example. For more on this see
http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html
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Hi, I build pp45 amps, I’m not here to sell them, but have a few comments that I hope will be helpful.
first I would say that the power difference between 2a3 and 45 designs is a paper thing mostly, they tend to sound close-to equally powerful (or weedy depending on your speakers and tastes). They do sound subtly different but it’s more about the execution than the tubes per se.
next is the magnetics. I use the best vintage Japanese magnetics i can find, along with USA UTC parts when I can find them. Recently I made a pair and the only difference was utc vs hashimoto driver/interstage transformers, and they do not sound the same. I believe that the loading of the interstage secondary is a critical design point often glossed-over in schematics. The loading network needs a lot of design and measurement to get right.
i use exclusively Sowter 1475 phase splitter transformers and fully balanced from there on through the driver and power stages. However, sorry to have to admit this to any zealous tube-only folk among y’all, I use a transistor discrete opamp (did he just say opamp?) to drive the single ended Sowter primary (sonic imagery or sound skulptor). There is no global feedback.
of course I would say this, but these designs based on 1930’s schematics, 1940’s valves and 1960’s magnetics sound pretty damn amazing and have great clarity and sound-stage.
there is something about pp that is overlooked: the output and interstage transformers fall in and out of magnetisation at every zero-crossing of the signal (at every polarity change). That is where the transformer is at it’s least linear transfer function. Se amplifiers are different: the opt never falls out of magnetisation, never polarity reverses and always operates in its most linear region. I am convinced this is a major reason they sound different, and some would say better, than pp types using the same tubes and supporting electronics, harmonic odd/even signature aside.
last comment about bass: this is tricky to comment on. Valve amps have feeble damping factors compared to SS, but is that a good or bad thing? It’s hard to give a definitive answer, and it’s more about the speakers and the room as to whether the ‘sloppy’ bass of valves sounds better than the ‘tight‘ Bass of SS, it can go either way, so keep minds open on that… my opinion is the low damping from tube amps works pretty well with closed box speakers, but that high damping factor is necessary to control reflex port behaviour. Not sure about dipoles though.
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Phil, if you can't see it on the scope, that does not always mean it does not exist. But it does mean that its pretty slight- if you have a really high bandwidth scope (200MHz and higher) that stuff usually shows up pretty well if its there.
However P-P is prone to harmonic distortion that SETs are not. A lot depends on the topology of the amp. For example if the amp is P-P at the output but combines single-ended circuits in the front end, the result will be that is has a 2nd harmonic that predominates, with a 3rd and a 5th also showing up. This is because the Single-ended distortion is compounded by the later stages and even though P-P can cancel even orders in the load, it can only do that with distortion that is also generated by the output section itself, not the driver or voltage amps.
If on the other hand if the circuit is fully balanced the only harmonic that shows up is the 3rd. This is because even orders are cancelled throughout the circuit. A lot also depends on the inherent linearity of any of the circuits; if things are bit off other harmonics and IM (inharmonic) distortions can show up pretty fast.
Its my opinion that P-P has gotten a bad rap in this regard, mostly due to some sloppy design and execution. To me this is very much a baby and the bath sort of thing. |
It's also possible that something about the wave hand-off in push-pull is audible, that may not be measurable notch distortion and being something else doesn't show up on a scope. I've discussed that possibility with some amp designers and EEs as well, but for lack of another way to reference it the phenomenon inherits the notch handle.
Phil |
Thanks Phil for your reasoned response. I am basing my comments on the simple observation of the amps themselves on the bench. I've seen crossover and notch distortion in transistor amps (which in some cases it was possible to correct by adjusting the bias) but in a good number of tube amps its just not something that shows up on the 'scope like it does with transistors.
I *have* seen it at higher power levels in amps that were malfunctioning. But never in a functional amp- an example is the HK Citation 2, which I have always held in high esteem. You can run it to full output and no sign of crossover/notch artifacts.
I have to admit to having far less experience with class AB2 amplifiers. They seem to be uncommon in home audio. However in AB2 we have the problem of the driver circuit which has to be able to maintain linearity when the tubes are in the grid current region. If this circuit is not up to the task you will indeed see artifacts- but in my comments earlier I was careful to use the caveats of proper design and proper functionality. |
>>...even if you run class AB1, you still don't run the risk of any crossover artifact, since at lower power levels where the crossover artifact might occur, the tubes are in the A region.<<
Agreed, but you seem to be presuming that notch artifacts aren't audible at higher power levels. I disagree. I once had a conversation with Julius Futterman about this back in the '70s. Yes, it's a long-running topic! There was an EE with me who also designed and built his own amps. We were listening to Futterman OTL vs. an old rehabbed Altec SET vs a Marantz 8B. Julius was listening to the two of us arguing about the audibility of notch distortion in push-pull vs SET. The EE was calling nonsense. Julius was smiling and interrupted. "Of course you can hear it, especially at power above the Class A bias point. It's just that most people either aren't sensitive to it, don't care, or they hear it as more texture." He finished saying something like "I'm an old man and I can hear it, but who cares? People want good bass and power so that's what we give them!"
He liked that Altec, btw.
>>What I have found is this is more a problem relating to solid state than tubes, on account of how the output transistors are biased. In tubes, in only seems to show up if there is a malfunction or design defect. <<
I agree with you on the transistor observation. Where I agree less is the implication that notch is not apparent in tubes used P-P. P-P pentode and tetrode make it more obvious to me than P-P triode, generally. And among tetrode amps it is least objectionable to me in the very simple Quad II.
You're the professional amp designer, Ralph, so you don't need me to confirm that you're absolutely correct about your phase inverter observations, but nevertheless I agree unequivocally.
Phil |
Phil, even if you run class AB1, you still don't run the risk of any crossover artifact, since at lower power levels where the crossover artifact might occur, the tubes are in the A region.
What I have found is this is more a problem relating to solid state than tubes, on account of how the output transistors are biased. In tubes, in only seems to show up if there is a malfunction or design defect.
IMO this is a very common myth! However, that is not to say that an SET does not have certain desirable qualities. Chief amoungst them is the ability to have distortion linearly drop to zero as power is decreased. This is where SETs get their 'inner detail' they are known so well for.
Most phase inverters in P-P designs introduce their own kind of harmonic distortion (having nothing to do though with crossover distortions). It is this additional harmonic distortion that causes P-P amps to often have increasing distortion below a certain low power level. It can be designed out by avoiding the use of stand-alone phase splitter circuits- by instead integrating the phase splitter function right into the voltage amplifier stage. This eliminates the need for a separate circuit and the less signal process the better (IMO). Traditionally the best way to do this is with a differential amplifier for the voltage amp. |
>>This is something that should not happen with a DHT p-p design.<<
Yup. Assuming push-pull class A. But what about Class AB p-p designs using triode power tubes, or for that matter p-p voltage amplification sections using small signal triodes. A push pull design *can* forego notch grunge but not every designer elects to.
DeHavilland made a 75w triode push-pull amp built around a pair of 572 tubes. It was confusingly described as "100% pure Class A A/B." We see today an increasing number of push-pull triode amps with power ratings well above what could be expected from Class A push-pull and one of the effects is that they sound like Class AB amps and sometimes like Class AB amps that use tetrodes or pentodes. What's good for guitar amps (biasing AB toward B for sparkle) doesn't always benefit hifi.
Phil |
Phil (213cobra)
You raise an interesting point, the quality of the output transformer and power supply are so critical to what you'll hear with a SET.Get those done to a high standard and sit back and enjoy. Compromise with those aspects and you will never know the full potential of this type of amplifier. It's true for all topologies but seems more so for the SET. |
subtle push-pull crossover notch grunge This is something that should not happen with a DHT p-p design. Crossover or notch distortion are artifacts of transistors and designs that are not class A, unless there is a serious design defect. I have a pair of type-45 amps that I have been playing at home for several years. They started as 45 SETs, but on examination of the internal circuit it was obvious they were candidates for improvement in the wiring, parts and input circuitry. With each update the amps sounded better- more detailed, smoother sound, etc. Ultimately I pushed them to a P-P design and the improvement over the SET version was dramatic! I think they can be improved further, but its been convincing enough that I just play them for the most part. |
Just remembered that I have heard the VAC Renaissance amplifiers which are DHT push pull.It's been quite a while but I really liked what I heard from them.
Regards, |
Agree,implementation of a product is crucial to the actual performance
level. I'd also prefer a well design and built PP amp over an average SET
amp . However if both are done at a high quality level then give me The
SET.I find the level of involvement and emotional connection with music is
for me unmatched.I react to them in a very spontaneous way, head
nodding, foot tapping, humming, imaginary playing along with the
musicians etc.They provoke a lot of goose bump moments and completely
satisfying immersion into the soul of music. These are attributes that can't
be measured yet are so powerful when present.Other amplifier
types can do this(to various degrees) ,but in my experience not nearly as
often nor as deeply
felt.SET amplifiers won't be the answer for everyone but they are ideal for
me.I haven't any experience with the DHT push pull amps, just the pentode
tube types (I like them wired triode rather than ultra linear).I wonder how
much I like is actually due to the DHT tube genre itself.They seem more
musically natural and present more realism then IDHT tubes (well to me
anyway).
Regards, |
Generally, if you seek SET sound, it will be better to listen to a 300B SET amp than a 45 push-pull, though if both are executed equally well, the push-pull amp will yield more disciplined bass. Getting the deep bass equally controlled from 300B SET will usually require a higher level of execution, particular in the output transformers but also in power supply, at higher cost.
It may take some careful listening to discern it, but if you have similar power and execution push-pull vs. SET for time-adjacent comparison, you may discern the presence of subtle push-pull crossover notch grunge. If you don't notice it, no problem. If you do, once you hear the absence of it in SET it's hard to live with crossover notch haze and grunge in p-p topology ever again. It's least noticeable however with triodes.
Usually push-pull at same power and execution level as SET will give you better bass definition and more slam. Top end attack may be sharper too, but this will very much depend on SET voicing as well as on the choice of power tube brand, materials and plate type. In a 300B SET amp, there can be a substantial difference in voicing and dynamic character between a mesh plate Chinese tube and, for instance, a KR solid plate. There's a lot of variety in 300B tubes now.
The holistic tone and unity presentation of triodes in single-ended topology has an organic and harmonic completeness that is elusive if not absent in push-pull, despite the push-pull implementation almost certainly measuring better. Execution counts for a lot. A superior push-pull triode amp can easily beat a mediocre SET implementation, On all the qualities you'd assign to SET I the first place. Put another way, either topology has to be done right. Still, the opening postulate above applies.
Phil |
Larryi,I agree, certain large scale music if loud enough can push a SET to its limit. No amplifier is best at everything, some amps are better for the example you gave but then those amps would fall short elsewhere. The Takatsui-TA 300b is superb and I much preferred it compared to a re-issue WE 300b in my amplifier(the 'vintage' WE 300b is just too costly).The Sophia Royal Princess is excellent in my amp(close to the Takatsuki in sound quality). I just ordered a pair of the EML mesh plate 300b(a true woven metal mesh tube). I `ve been very curious to hear what this tube is capable of compared to the Takasuki. The EML has developed a quite a reputation for good sound and reliability.
Regards, |
Charles1dad,
We are in agreement about the strength of SETs. At higher volumes SETS remain remarkably composed and do not fall apart--they just stop getting louder as their limit is reached instead of breaking up. But, because they do produce so little power compared to other forms of amplification, they can sound compressed when played at higher volumes because they are really being pushed too hard. This is not that evident with most music, particularly pop-rock or jazz. To me the dynamic limits of amps are most evident listening to large scale choral works, such as Rachmaninov's Vespers--I can hear compression at what seems modest volume levels with this work.
You mentioned, above, the Takatsuki 300b. I've never heard that tube. What would you say is the tube delivering sound closest to that tube? I know the Japanese are big fans of Western Electric, so I would guess that is the kind of sound they would try to clone. Of the 300b tubes I've heard, I like the one Kron put out about 10 years ago--quite punchy and lean compared to most 300bs. |
Larryi,
I find with a good SET amplifier I can expand the usable volume range in
either direction. At medium and lower levels they maintain a healthy sense
of pace, flow, dynamic contrast and remain very musically involving.The
transparency, tone realism and full body preservation seem responsible for
this. Conversely I can listen to complex music at high sound levels and
everything remains clear and very articulate, it all stays connected and
holds together well. Probably the big advantage for me is they avoid the
dreaded over emphasis on transients and the artificial edge and sharpness
it brings.You get the natural attack yet preserve the decay and the sustain
that I find vital for realism and avoids that hifi mechanical presentation I
often hear with other types of amplifiers.Larry, I agree it'near remarkable
the difference the brand or quality of a tube or amplifier can make within a
certain genre.
Regards, |
Thanks Larry that's a fair observation and good info... |
Jsman,
That is a tough question. It is not so much a case of some huge difference, as so much a matter of degree. In many respects differences between tube types-- 45 vs. 2a3 vs. 300b vs. 211 -- is more significant, and arguably difference between brands can be on the same magnitude (for example an EML meshplate 2a3 will sound VERY different from a JJ meshplate 2a3).
If one is comparing "like" amps-- pushpull 45 vs. SET 45, or PP 2a3 vs. SET 2a3, the SET amps tend to develop a more enveloping soundstage so one feels more emersed in the sound. A really good SET amp is surprisingly dynamic and lively sounding at lower volume levels (the lower one goes in volume the bigger the advantage of SET amps). Good SET amps sound relaxed and lacking in artificial edginess, while to sounding murky or sluggish.
But, good pushpull triode amps, are pretty good too in all respects. The sound of such amps tend to be punchier and tighter (less overhang on notes), and hence, they tend to have a more driving rhythm. This is good if one's system is a bit too polite and laid back. But, an over emphasis on rhythm and drive can give the music the "mechanical" quality I mentioned in an early post. So good quality can become bad, depending on ones taste, system, perhaps type of music, etc. This tighter sound also means that notes seem to decay faster and so there is less of a lingering "wash" of sound (again, good or bad is a matter of taste).
I happen to like both pushpull and SET triode amps. I certainly tend to prefer such amps over higher powered pentode and tetrode pushpull amps. Most of these kinds of amps sound a bit too brittle and edgy to me, and they tend to be lean sounding (lacking in full saturation of all the harmonics). Also, they tend to sound dead and lifeless at lower volume levels.
I am pretty much a low power amp fan. To me, one can tell how good an amp is by how LOW one can go in volume and still enjoy the sound. |
Larryi,
In your opinion what are the ear opening differences between the PP and the SET amps you have heard in your system? |
Nice post Larryi, no single amp topology does it all.SET is`nt perfect across the board(what is?) but their natural presentation and non mechanical sound is more emotionally real and involving IMO.
Gsm18439(Gary) you`re right, it`s difficult to generalize 300b sound. Depending on the brand they vary from soft,slow and rolled off to simply brilliant sound(Takatsuki-TA) and all stops between these extremes. There are many flavors of 300b tubes.Of course the quality of the individual amplifier is another 'huge' variable.
Regards, |
My only experience is with SETs. However, 300b SETs are much more tube dependent than 45 or 2a3 SETs. . . so much so that it is hard to make general comments about 300b SETs without mentioning the type of tube used. |
I have a Deja Vu pushpull 45 amp. I like the sound. It has a tight, dynamic sound that is characteristic of pushpull. It is a VERY good amp. However, SETs do some things better (I own a parallel 2a3 SET amp). SET amps have a more natural delivery--no artificial edge to the initial attack, notes seem to bloom and expand into space, and the sound is more enveloping.
SET amps are often characterized as being a bit short on dynamics. Most often this is really about bass delivery. SETs don't quite deliver the same kind of "punch" to bass notes. I have mixed feelings on that issue. That same "punchy" sound of pushpull bass can sound a bit mechanical and artificial to me (sounds the same no matter the music), while SET bass tends to have more character (changes subtly with the music). But, the extra punch of pushpull may be what some music needs, so it is hard to say what is better. I currently have in my system a pushpull amp I really like (output tubes are Western Electric 349A), so I am not really in one camp or the other. |
You can debate whether you prefer SET or PP amplifiers. They definitely sound different; I think each would appeal to some. Obviously, push-pull gives the kind of advantage in power that allows most to use the triode tubes with a real world loudspeaker.
The 2A3 has half as much power on paper in comparison with a 300B, but real world seat of the pants power doesn't translate, and the 2A3 often sounds like the bigger tube. The 2A3 is also the better sounding tube, and the 45 better still. However, the 45 makes half as much power as a 2A3, sounds/feels that way (figure 3 - 6 watts for push-pull 45 amplifiers), and seriously limits your loudspeaker selection. |
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Apprently they are rare- I have a friend that made a custom PP2a3 that could be converted to PP45 (I already have an SET 45 from him which is great- it is an awesome tube), so I am curious how it would sound as well. I can only guess that if the reason for wanting more power from the 45 is why the reason to creat a PP version, at that point people might be thinking a 300B instead at 8+ watts, hence the popularity of those amps. It would be great though, to see more 'all-out' 45 PP designs... |
Are you telling me that no one here has owned or heard one of these types of amps??? |
