SET vs OTL

The autoformer used as an impedance matching device is, in effect, an output transformer.  It is doing exactly what an output transformer does.  To me, if something sounds good, I don't care how it got there.  I've heard many great tube amps, and I would not dare to say if any particular topology beats out another.  My personal favorite happens to be an OTL amp, but, it is an utterly unique, one-of-a-kind design.  A very close second (maybe not even second) is a pushpull amp that is extremely rare and costs six figures for a pair (Western Electric 59A).  I own a pretty good SET amp (Audio Note Kageki) and I've heard many other good SET amps, but the amp I currently run in my system is a low-powered pushpull amp.  

In a nutshell, hypothetically, if the speaker is a "very easy drive without any hindrance" at all to either amp, the OTL in class-A will be the better amp full stop.

BUT!! for an OTL not to be hindered IN ANY WAY at all by todays "better sounding speakers loads" that have NOT had "their sound compromised" (because they were designed "firstly" too give a very easy load), is a big ask.
And those type of "very easy to drive speakers" usually have big other glaring problems to many listeners that are susceptible to their colorations,  so it’s a bit of a catch 22.

Cheers George

My speakers are Duevel Bella Lunas with 6 ohms impedance and 93db efficiency. To run the Graaf I used Paul Speltz Autoformers to step them up. I used Bybee Golden Goddess Speaker Bullets in both instances and Auditorium23 speaker cable. 

"In a nutshell you have to be really careful about making broad stroke statements; when comparing SETs and OTLs it can go both ways insofar as to which comes out on top."

Agree and it absolutely does go both ways. This topic has been discussed numerous times on this and other forums. I’ve compared SET and OTL directly and would choose SET just as @antigrunge2 did.

@audition_audio has done similar comparison and finds OTL superior. Okay fine, his experience and good for him. We don’t need proclamations, just choose what you conclude is better. I’d never declare SET universally superior to OTL, NOR would I do the converse.

Plenty of music listeners have made the choice for OTLs and plenty have done so for SET. Why do we need to draw lines in the sand and have turf battles when it comes to audio components and listening preferences? People have moved on from SET to OTL and from OTL to SET.
Charles

I have used a Graaf Gm20 for about 10 years before upgrading to a Wavac Ec300b some 10 years ago. In short, there is no going back: while the Graaf had twice the stated output power, making that power useful was challenging: using autoformers to ideally match speaker impedance as well as pretty regular rebiasing, neither of which is required by the Wavac. If anything, the Wavac is faster than the Graaf despite its transformers and the bass is substantially more solid. Botj amps are classics in their line of design

What speaker were you using for this comparison? 

The speaker can be an enormous influence when doing comparisons. There are other variables as well- for example most OTLs employ feedback (ours are some of the very few that do not). Some OTLs use pentodes as opposed to triodes. So they sound different; you can't categorically state that because you've heard one OTL you've heard them all and actually be telling the truth.

The distortion signature of the amplifier also plays a big role in the results. In a nutshell there are two types of non-linearities that show up. In single-ended circuits you get a quadratic non-linearity. In a differential circuit you get a cubic non-linearity. The cubic is preferred because its lower distortion; this is because even orders are cancelled and distortion does not compound as much from stage to stage as the signal progresses through the circuit. The 3rd harmonic is the primary distortion product and will mask the presence of the higher orders, allowing for a very smooth sound, but more detailed that that of a single-ended circuit because there is less distortion to mask it.

In a single-ended circuit the primary distortion product is the 2nd and there is usually a prominent 3rd. These two harmonics mask the higher orders so this circuit sounds very smooth as well. The problem is that as the order of the harmonic is increased, its amplitude falls off at a slower rate, causing more low level detail to be masked. But it has a rich sound due to the prodigious 2nd harmonic created.

When you combine the two (such as a single-ended input with a push-pull output), as a good number of OTLs (and other push-pull amps) do, algebraic summing occurs and there usually results more of the 5th harmonic (this has been known a good long time as Norman Crowhurst was writing about this 65 years ago...), which is the main reason SET guys object to the 'sound' of push-pull. But if the PP amp is fully differential you don't have this problem.


Since the feedback used in any tube amplifier is insufficient for it to really do its job, these distortion artifacts remain in the distortion signature.


In a nutshell you have to be really careful about making broad stroke statements; when comparing SETs and OTLs it can go both ways insofar as to which comes out on top. But all OTLs are **faster** than any SET (simply out of the fact that transformers slow down risetimes based on their bandwidth limits; this is simple physics); if it sounds 'slower' its likely because the amp is not matching well with the speaker in the high frequencies.

Well actually no! True the quality of the iron as well as the circuit and its design do contribute and can make significant improvement in any amp design, the absence of a transformer contributes hugely to the intrinsic difference in sound. Provided that the amplifier requirements are met, I think an OTL is a superior design. 

Antigrunge,
What speaker were you using for this comparison? 

Phantom a/v is correct in that impedance is crucial with OTLs which can be a serious impediment. Your experience mirrors mine. What amazed me was how quickly the SETs we used in the comparisons went into soft clipping. They got more muscular but confused sounding. It took hours of listening and direct comparison to figure this out. 

@antigrunge2,
It is interesting how people hear audio products and how it formulates opinion and decision making. Some OTLs may sound faster than some SET amplifiers. Some do not. Your experience with the Graaf and Wavac is similar to mine.Ive heard SET with as much "speed" clarity and transparency as fine quality OTLs. Some may experience "sweetened" or "lush" coloration with certain SETs but they all are not the same.

I would caution against painting with the proverbial broad brush. My SET is organic and full of tone/body, very natural and has an  emotionally engaging presentation. There is no sacrificing of nuance or natural detail. There are many variables that determine what works best for a given listener and their respective audio system. Many roads do in fact lead to Rome.
Charles

I have never encountered a SET amp that even came close to an OTL when using an OTL friendly speaker. The difference is startling. I find this true of P.P. designs as well. 

I have used a Graaf Gm20 for about 10 years before upgrading to a Wavac Ec300b some 10 years ago. In short, there is no going back: while the Graaf had twice the stated output power, making that power useful was challenging: using autoformers to ideally match speaker impedance as well as pretty regular rebiasing, neither of which is required by the Wavac. If anything, the Wavac is faster than the Graaf despite its transformers and the bass is substantially more solid. Botj amps are classics in their line of design

I own both SET and OTL, but most of the time i kinda just use the OTL Amps more often than SET Amps.

The only thing i can input from personal experience is No SET has come as close to the Speed, Dynamics of an OTL.

Owning both i like both SET and OTL and sort of kinda prefer the OTL on every genre of music. Hip Hop, RnB, Dance, Trance, Drum And Bass, Techno, Rock, Movie Scores, Demanding Classical Acoustical or Opera Music I still feel OTL Wins hands down to faithfully reproduce this sort of music.

Whilst it sounds very good on SET amps with more Lush, you can still easily tell the tempo is not exactly the same. Details are lost, slight muddiness to the music playback, this feels like a veil on the speaker, small soundstage than my OTL amps, Slower in pace, the bass is not as articulate or lower in registers. All this is only evident when you do a direct comparison to an OTL.

SET Can sound glorious and Lush/Sweet. it does so with more compromise to details, Resolution. Bass depth and speed. 

Live music is not Warm or Lush or Sweet, since in a Venue or opera house or in a Jazz Club, Its not ever Sounding Lush, Sweet or slow. These are all artificial sweetness added by different SET Circuits.

The biggest problem i find with OTL is that their real magic only takes place when a 16ohms speaker is used. Whilst 8 ohms its still far better them most SET, the real magick only happens on 16ohms or higher.

if only you could design your own OTL,then you can say this is better.

OTL of course is way better than any SE.

Ralph,Bruce has it and probably a lot of DIY OTL.
Charles,If ever there is a fest,we could find a way to A-B things out..

I don't really understand where the comparison of SET and OTL amplifiers really takes a person. there are members of this site who have owned Atmasphere or Joule OTLs and subsequently moved on to a SET amplifier.  Conversely there have been SET amplifier owners Who subsequently moved to an OTL.  This traffic clearly moves in both directions, there are simply many variables involved not the least of which is personal preference and taste. Various brands of OTL amplifiers sound differently, same is true for different brands of SET amplifiers. Change the brand of the output tube, again more variables and different sound, on and on it goes.

There is no definitive way to say one topology is superior to the other. Either can sound fantastic, or just okay. Design, The builder's talent and implementation tell the story.
charles,

I would say that a well designed SET 2A3/300B  has the warm sound than also well designed an OTL having the same output wattage.

There really aren't any OTLs that make the 2-7 watts as suggested by the above post. OTLs become less practical at lower power levels- driving the real world impedances that one might do with a transformer-coupled amp gets harder. That is one reason OTLs tend to have a lot more power than SETs, and is why our smallest amp makes 30 watts into an 8 ohm load. To make the amp much smaller than that becomes impractical.

However I have found that the OTLs tend to make less of what I have come to call 'loudness cues', IOW higher ordered harmonic distortions (which show up in most SETs when driven over about 20-25% of full power). The result is that the OTL won't sound as loud (even though it is probably louder) and so invites you to use the power it has. This can be done comfortably. The reason SETs sound so dynamic is due to distortion and how that interacts with the ear, not actual volume!

It's hard to argue in words and win the war,what we need is to A-B these things  side by side and I hope somebody will initiate  a fest for audio fanatics  into reality. 

The one thing that I might add is that 300b tubes can sound very different depending on design and manufacturer. Some 300b tubes sound much more linear than others. Conversely, my experience with different 2a3  tubes (while admitedly more limited than my experience with many different 300b) suggests that they are more alike than different.

I would say that a well designed SET 2A3/300B  has the warm sound than also well designed an OTL having the same output wattage.

Larryi, I should have mentioned that I agree with you that even with the flaws of the AN-e's they are just so musical and emotionally involving that I cant imagine selling them, ever. I've had them for four years and even when I hear systems or speakers that sound better than what I have, I am almost never tempted to upgrade. The 300b is a warm tube but its got some power and in my room and system some slam and good extension in the low and high frequencies.

Would be great to hear on OTL in my listening room someday.

Jet,

I find that the upper bass on the AN-E, as well as other Audio Note models, can be a bit bloated, but, it is a very musically enjoyable speaker so, if that is a flaw, so what?  I am not as big a fan of the 300b as I am of other small triodes (2a3 and 45) because the upper bass and lower midrange is a bit overblown.  But, as you demonstrated, things can be tuned to ameliorate these sort of issues.

I have heard an OTL on the AN-E SEC and the sound was fantastic.  I think it would be worth your effort to find an OTL to try in your system.  The Atmasphere M-60 should be a good candidate.  It is on the slightly leaner side, so it would not exacerbate the tendency of the AN-E to sound a bit bloated.  All three M-60s I've heard had a slight bit of buzz or hum, but, given that the AN-E is not extremely efficient, I doubt that this noise will be much of an issue.  

The Audio Note AN-e LX HE is a fairly benign load and is no problem for an OTL of sufficient power- our customers use our M-60s on that speaker. The speaker definitely benefits from the greater power!

Every OTL I have heard had the quality of being very immediate and exciting sounding; the music comes alive to a degree I have never heard with solid state amps.  But, that is not to say that some pushpull and SET amps don't do the same, it is just not a common characteristic of other types of amps.  OTL amps, like amps of  any other topology, sound different from each other based on tube choice, voicing by the designer, choice of other components, specific circuitry, etc.  The Atmasphere amps, for example, are leaner sounding than the Joule amps I heard.  Which is better depends on taste and system matching.

I have no idea which form of amp is superior to the other.  I run fairly efficient speakers (@ 99 db/w), so I can use a pretty wide array of amplifier types, including low wattage SET amps.  I have two pushpull amps (45  tubes, and 249 output tubes) and a SET amp (parallel 2a3s).  I don't know if I really have a "favorite" between the SET and the 249 pushpull amp (I currently like the 249 and have it in my system, but, I like certain things about the 2a3 SET amp).  One of my all-time favorite amps, however, are OTLs that a hobbyist built that two people I know own.  Another great amp I heard is a Western Electric 59A (252 meshplate output tubes) which is a pushpull amp that is incredibly dynamic and exciting sounding (also insanely expensive).  So, I have no idea which approach is superior in delivering the sound I like, much less what anyone else would like.

Lets be transparent with  OTL what is bad and what is good about it not just trying to promote your own product.I know that most all pre amp are OTL.Not all OTL are the same.I hope we can Blind test  otl out there

Ralph,
Why let appropriate linguistic usage get in the way of a good hyperbole? Well... in other people's cases it's hyperbole. In mine, it's just plain fact (if only I could figure out which ones).

Everyone says they have the best. In the English language, the meaning of the word requires that there can be only one. All the others are then 'better' but not 'best'.

This has been argued a lot elsewhere on this site. Any consensus on the idea of 'best in my experience'?? instead of merely 'best'?

Paulfolbrecht,

I have one of those Pavel designed Deja Vu PP 45 amps (it also can run 2A3's) built around two big Chicago circa 1950 output transformers and it is indeed one of the best if not the best amps ever made. And it can drive some pretty inefficient (89db) speakers such as Spendor SP 100s, DQ 10s, Soliloquy 5.3s Quad ESL 63 to name a few. I use vintage RCA and Cunningham 45s and RCA biplate 2A3's which gave me the best results although I also have used Sophia mesh plates, KR, Sovtek, and VAIC 2a3's.The amp uses 6sn7 input tubes.

I know someone who says those PP DevaVu 45s are the best amps ever made.

Paul,

The pushpull 45 amps were built by a Russian guy named Pavel and were sold through a Washington, D.C. area dealership (Deja Vu Audio). These amps used Acrosound TO-330 output transformers (the feedback taps not employed, obviously). The wiring was all point-to-point. In fact, Pavel laid out the amps so exquisitely well that there was almost no wire used in the amp (lead-to-lead connections).

I have one of these amps, though mine uses solid state rectification (most of Pavel's amps employed tube rectification). Some versions used big Chicago brand transformers.

I like the sound of these amps very much. But, my current amps (Audionote Kagekis) are, better to me (at a HUGE price premium).

Deja Vu Audio is an interesting store. They will run almost any speaker with low-powered tube amps which "conventional wisdom" says are way too underpowered. The store sells Quad speakers, and even the 2805 is connected to a fairly small tube amp. The one solid state piece in the store is a Halo JC-1 amp. I asked about it and was told that it is used purely for comparison -- Vu, the proprietor, wanted a decent, high-powered solid state amp for a reasonably fair showdown.

Said I owned over 35 SET amps 6 of them-45 SET, 4-OTL. Not that I'm 35. Would happily trade to be 35 again. I will leave this thread nothing worth while here. All I do is design hi-eff loudspeakers mostly for small power amps like SET what the heck would I know about driving loudspeakers with small power or OTL.

Paul & Larry,

Thanks for the input.

Marty

PS Paul, I have a different view of crossing subwoofers, but I'm really interested in trying a 45 SET full range, anyway. I'll explore the Audionote further.

Larryi,

First of all I acknowledge that this is something of a matter of taste and also system-matching - as you pointed out, a ripe, bloomy mid-bass *can* be an attraction!

It isn't in the systems I've put together.

EML makes very good tubes but their 300B retains the tube's bass characteristics IME. They may go somewhat lower than most but it is not an tight & controlled, nor as linear in the midbass region, as the 45 - especially the EML 45.

Not sure if you heard an HE version of the AN/E but if not you're talking about 3 dB lower - right about the power difference of SET vs push-pull.

What were the PP 45s you heard?

Although I am one of those that expressed a personal preference for 45s and 2a3s over 300bs (I own a pushpull 45 amp and a parallel SET 2a3 amp), I hardly think it is fair to say someone is wrong or inexperienced for have a contrary preference. A friend of mine who owns more than a dozen different amps, many he built or modified, prefers a 300b SET amp for his setup. His custom horn system is 105 db/w efficient and his room is not very large, and he listens at fairly low volume, so power is NOT an issue. In this case it is more of an issue of system matching. The horn loaded bass driver does not go low enough for the punchier, better controlled deep bass of 45s and 2a3s to matter as much, and the slight leanness of his system's upper bass/lower midrange is nicely compensated for by the upper bass bump of the 300b. This is a case of different horses for different courses so no there is no absolute superiority of one over the other.

Martykl, I've heard AN/Es being powered by pushpull 45 amps in a very large room and was actually surprised by the volume that speaker can deliver, given its somewhat modest efficiency. I don't know how it would have sounded with a 45 SET amp however (SET would be roughly half the power). I prefer that speaker a little bit away from the corner because its bass response can be a bit too much in the corner. Because Audionote speakers have a fairly warm warm upper bass and lower midrange response, I would have some concerns with 300bs overemphasizing these qualities. Still, one never knows without a trial.

One more thing to add. There are certain 300b tubes that are better at controlling bass and reducing their loose and overripe upper bass response. I am talking about the Kron 300b. It is no longer made, though new stock is still available. Because of the close relationship between Kron and Emission Labs (EML), it would be worthwhile looking into EML's current production 300b (I use their fantastic 2a3 tubes myself).

Martykl,

If you use a powered sub but with high-level inputs - as many people believe is preferable - the bass characteristics of the amp still matter - except for power (current) delivery.

Yes, the HE AN/Es work very well and really do give usable bass to 20 Hz positioned in corners as designed - flat to 30. (I'd say peaks to no more than 85-88 dB in a large room, however. Small room, obviously louder is possible. But AN/Es tend to overload very small rooms with bass.)

I know for certain there are people who have used Zu Definitions with 45 amps with very good results. Those have powered bass, good to close to 20 Hz I do believe.

Paul,

I understand that SPLs will be limited when using a 45 SET amp full range. I am willing to restrict my use of such a system accordingly. I am, however, intrigued by the idea of an SET that can deliver the mid-range I have come to expect of such designs (based primarily on my 300B experience) with superior bass response. To be clear - I don't expect LOUD and I don't expect 20 hz.

I can (and have) used powered subs with my 300B amps. This does not address the point that the 45 lovers here have made regarding the superior bass performance of these amps. If I use powered subs, I don't particularly care about the bass performance of the main amp - 45, 300B, or SS.

If I understand the rest of your post, the Audio Note HE version might be a good choice. Any other ideas? Anyone try the Zu for this purpose?

Marty

I sell 300B amps to folks who need or want them. I would never recommend a 300B when a 45, PX-25, 50, or 2A3 would suffice.

All things being equal, i.e. the speaker can be driven by any amplifier, the 45 kills the 300B all day long.

Anybody with half an ear would know that.

Perhaps even you John.

Your experience?
LOL, when you get to 50 years, we can talk.

Never said 300b is the best just that I disagree that 45-50 SETs the best for nothing ever is truly the best. You speak in adsolutes as Masty pointed out. And Bill sure Ive owned far more flee powered SETs than you think over 35 at least want pics? But I will take your sugestion Bill and ignore you. Instead I will listen to my collection of SET amps. On my many hi-eff loudspeaker designs take the day off. Bill sells 300b amps to folks bet he doesnt express his preferance then.

Now, I happen to like JohnK, and some people do prefer the 300B. I never quite have - but they do have their own strengths and can sound very nice (of course).

Surely they have the ability to drive well speakers that 45s can't hope to.

[I meant to point out that my TBI subs are driven from high-level (amp) outputs, meaning I am hearing the bass signal produced by the amp, not the preamp.]

Johnk has no clue but he talks a good game.

If he had experience with flea power SET amps that Paulfolbrecht and I do, his comments would be somewhat valid.

Ignore him.

Typo - of course I meant 100x the power required from 80 dB to 100.

Martykl,

You really can't ask a question like that without specifying your desired loudness level. 80 dB vs 100 dB - 10x the power!

I recently spent some time driving the 90 dB/W DeVore Super 8 with a pair of 45 monoblocks. I tried it at first just as an experiment, and I discovered, with listening levels of 80 dB on peaks in my large room, the (jazz) bass lines were incredibly articulate - perfectly sculpted. *Much* better than the 300B monos I'd just been using.

Is this a recommendable real-world combo? No, of course not - not unless you listen pretty quietly! My point is that, despite the inappropriate pairing, I could still evaluate the bass of these two sets of amps - and, in both cases, it had exactly the characteristics I have come to expect from these two output tubes. (And, while, again, not recommended, this combo was so good I left it setup this way for weeks. I'm trying to train myself to like lower SPLs anyway - and with this setup I could.)

If you want examples of speakers that can be driven cleanly and dynamically to moderately loud levels with a 45 SET amp, and have bass flat to close to 20 Hz, I can give you two: HE versions of Audio Note AN/Es and Supravox field coils on open baffle. The latter supported by powered subs (TBI) below 50 Hz.

If you want LOUD levels, I think you have to go to front horns and/or speakers with powered bass modules (Zu, others).

John,

Glad to provide a laugh.

Your last comment is interesting in that I had posted earlier looking for info on loudspeakers that provide:

A) Appropriate sensitivity and load for a 45 SET amp

and

B) Sufficiently flat and extended bass response to even judge the bass capabilities of these amps (i.e.- no biamping).

Zu's full range passive (Essence?) looks like it might qualify. Any thoughts on this or other candidates would be appreciated. Again, budget and availability are considerations here.

Marty I thought your post was funny.

Bill I have much experience with SET and audio design. Transformers mater as much as tube type not all 300b have weak bass rolled off hi. And as far as 45 50 SET as you say the best. Best for what? at 1.5 watts what can you drive? You need a loudspeaker designed to run off such low power and I have built many. And this low power doesn't drive woofers into low frequencies very well. Most of the loudspeakers I design for 45 SET etc have little bass below 40hz since 45 SET has little drive. If I want bass to 25hz or lower need biamping. So I agree 45 SETs best for biamping;) Its the transformer and amp design that gives extended range not the tube type. Bill with a bit more experience you will learn this. Take care and happy listening.

Robert,

I fear you may have misread my sarcastic comment which was nominally directed to Johnk.

Perhaps with a little more experience you will understand....my post.

Marty

Several years ago the late Terry Cain told me his favorite tubes are the 45's period.End of discussion.