What's the deal with SET? (Single-end Triodes)

[Ralf11]

is second harmonic distortion euphonic?

 

and what's wrong with the push/pull amplification?

 

- yes, this gets into some of the St. Vitus dance discussion... particularly with respect to the degree that measurements fully capture SQ

[Kimo]

is second harmonic distortion euphonic?

 

and what's wrong with the push/pull amplification?

 

- yes, this gets into some of the St. Vitus dance discussion... particularly with respect to the degree that measurements fully capture SQ

 

I have owned several SET amps, as well as a couple of push/pull ones. Also, had several more in and out of the system. I generally prefer SET, provided you can find the right speakers to get the most out of the amp. Easier said than done.

 

My biggest problem with the push/pull amps that I have heard is the lack of edge and detail. I understand this to be related to the transformers. I don't notice this loss as much with SETs. Nevertheless, push/pull seems to work well with more speakers and more consistently, even at the same rated output. SET amps can vary in sound more than a bit with different seemingly compatible speakers.

[accwai]

is second harmonic distortion euphonic?

 

 

[...] My biggest problem with the push/pull amps that I have heard is the lack of edge and detail. [...]

 

Not just lack of details, but lack of precision in both dynamics and tone. It's interesting that SET is usually characterized as euphonic, smooth etc. In reality, good SET matched with the right speakers usually sounds quite raw (in the good sense of the word ). And the dynamics of such combo is *brutal*. Believe it or not, everything else will sound vague and anemic once you have a proper experience of SET.

[Kimo]

 

 

 

Not just lack of details, but lack of precision in both dynamics and tone. It's interesting that SET is usually characterized as euphonic, smooth etc. In reality, good SET matched with the right speakers usually sounds quite raw (in the good sense of the word ). And the dynamics of such combo is *brutal*. Believe it or not, everything else will sound vague and anemic once you have a proper experience of SET.

 

For quite awhile, I used an Art Audio 845 Carissa amp, delivering 16 watts per channel. I primarily used single driver speakers with this amp, and everything seemed to work well. Speaker efficiency was high, though not crazy high. Tried the amp on a very efficient horn system, and its character changed a bit.

 

I remember the Fi X 2A3 integrated that I owned. Literally stopped playing on the 94db Living Voice speakers. Actually, the amp kept going, but the sound stopped. Switched to the 95 db Cain and Cain speakers and it sounded wonderful. Found out the amp was supposed to have been voiced on those speakers

 

I probably won't go back to SET. I have settled into the Class A Pass world, and found a multi way speaker with a tweeter that I don't despise. I would advise the curious to give SET a listen and decide for themselves. Just be sure as you can that the amp is performing with a speaker that allows it to shine.

[accwai]

For quite awhile, I used an Art Audio 845 Carissa amp, delivering 16 watts per channel. I primarily used single driver speakers with this amp, and everything seemed to work well. Speaker efficiency was high, though not crazy high. Tried the amp on a very efficient horn system, and its character changed a bit.

 

I remember the Fi X 2A3 integrated that I owned. Literally stopped playing on the 94db Living Voice speakers. Actually, the amp kept going, but the sound stopped. Switched to the 95 db Cain and Cain speakers and it sounded wonderful. Found out the amp was supposed to have been voiced on those speakers

 

Also be sure to experiment with different output impedance on the amp. As an example, the recent review of the Triode Lab 2A3i on 6moons has a little discuss on 8 vs 16 ohm output terminals of the amp feeding Ocellia Calliope .21 Twin Signature on page 3. The speakers in question have single 8" wide band main driver with twin supertweeters per channel. The main drivers are 16 ohm.

 

Just be sure as you can that the amp is performing with a speaker that allows it to shine.

 

Absolutely.

[MothAudio]

VAC pa 35/35

 

Moth Audio s45

 

 

I went through a coupe of push-pull amps before I settled on a VAC pa 35/35. This is a push-pull 32 watt triode amp with EL-34 output tubes. Also has volume control. Really liked that amp a lot, tweaked it with the best NOS tubes. That was 17 years ago. Then I kept reading about single-ended triodes and decided to sell the VAC and ordered a custom Moth s45 SET [with volume control] that could use either 2A3 or 45 output tubes.

 

Here's a collection of notes I kept in my online listening journal from that period....

 

 

Early Impressions: Moth vs VAC. Let me begin by saying, I enjoy my system MORE with the Moth than I did with the VAC. Even with the compatibility issues of the 2-5wpc Moth+93db Sonatinas I'm willing to live with the hick ups while savoring what the Moth does so right.

 

Perspective: The perspective with the Moth is more recessed, and the images more discrete, than the larger-gestured VAC. One is not better than the other, this is more an issue of preference.

Detail / transparency / naturalness: The Moth wins big-time. There is just more of a rightness that "appears" to convey a more accurate representation. Is it more accurate? I don't know, but it gives a better impression of live instruments in the room - timbrally. Transient speed / micro-dynamics: Again the Moth wins hands down. PRAT is much better, the music propels itself, like actual music-making. The rhythm section is much more connected to the source AND the listener.

 

Space / imaging: The VAC was very special in this regard. I'm still not sure how the Moth measures up. Obviously there is no clear-cut winner. I find the soundstage to extend further from the edge of the speakers with the Moth, and somewhat more dis-embodied from the enclosures in the near-field. But I'm inclined to say the VAC had more of a 3-D effect, where images have more freedom in the room, in the global sense. Sometimes images would appear from behind the listener, then move centre stage, then vacate. I'll have to listen for which outlines venues better, but I would think the VAC is superior in this effect.

One month update: Surprisingly images have increased in both size and perspective. Whereas images were much smaller in relation to the VAC and more recessed in the sound field, now they are more developed and forward, with wrap-a-round effect: Like swimming in sound or being immersed in an ambient dream. 3>. The concerns I had with leanness IMS are pretty much gone. Even with the more analytical 45s I'm satisfied with the realistic sense of body from instruments. The bass from either 2a3 or 45, though having different characteristics, has remained very impressive. The 45 kills the renowned bass performance from the Amperex double-d-getter EL34's, least IMS with the VAC!

 

 

The 45s are spooky in the way they dis-associate themselves from their enclosures. That openness I was referring to. Sounds hang more in space, something that wasn't lacking with the push-push VAC. I find that the lower output of the 45s (I'm speaking of the "ST", not the "Globe" 45) is offset by the incredibly engaging bass and swinging micro-dynamics. That the need for volume is reduced by the more lively sound. This is one of the main attractions of SETs: Enhanced dynamics even with lower volume coupled with greater listening ease which affords longer, more pleasurable sessions. This ease is due to lower output levels and the angelic presentation that is the hallmark of SETs. Imagine pristine smoothness and lighting transients - simultaneously!

 

Three month update. It's been 6 weeks since my last report. Now approaching three months with the amp, this is a good time to address some issues I may have waffled on in previous posts. If unclear, I LOVE THIS AMP! This speaks more of what the Moth does right than a lacking on the part of my old amp. With the prior grouping there was just a nagging feeling that something just wasn't "right" that I attributed to the VAC and now with just this one [1] change, there is a feeling of "rightness" with it. IMS/room, with my music (coupled with my replay preferences), this amp mated to my Sonatinas I could easily live with THIS setup for awhile, * it satisfies - Me!

 

 

* 15 years later I still own it.

[YashN]

is second harmonic distortion euphonic?

 

Wrong way of seeing it: In a SET, there is low odd-order harmonics, so that increases perceived SQ. The second order harmonics which are still extent have a distortion profile which sounds musical, much like if you play C on a keyboard at the same time as the C an octave higher, it sounds harmonious.

 

The existence of high 2nd order harmonics isn't a goal of SET.

 

A good SET isn't built to increase or emphasise the 2nd order distortion in any way. All distortions are minimised in a good implementation.

and what's wrong with the push/pull amplification?

The Phase change and need to recombine the two signals. This apparently makes for a 'disconnect' that removes some coherence to the overall sound. Some people are OK with having the PP do bass duties, so we can suppose that lack of coherence is less apparent in these regions.

 

Now, what's the deal with SET, on top of the above, I can tell from my own experience, since I have lived with SS amps for all my life before, so first I wanted to build a Tube amp (buying was over budget for me), and I took some time to look for a good topology to test. SET it was.

 

When I was researching, one thing I found many people say was the strength of SET Tube amps is in the mid-range (where vocals are, and many percussive elements as well).

 

My SET Tube amp does exactly that. The quality and the mid-range it provides was a revelation to me. More sounds, more separation as opposed to smeared, and micro-details, like low-level vibratos, etc... Presence...

 

Another thing I may have read but hadn't latched on but was verified in my setup is that a small-powered SET amp can give you a perception of power more than that of a much more power SS amp.

 

I knew my SET amp would do around 8W per channel in default configuration (I have yet to wire in the other configs, so these are untested).

 

But what was flabbergasting is actually listening and finding out that 8W could sound much better than 85+W per channel (that's my SS amp).

 

The SET amp renders fast and big attacks, like Kick drums with a continuously powerful presentation. My SS amp, for lack of better descriptions, sags...

 

Overall, my SET amp renders attacks and reverbs and thus timbre and soundstage in a much more convincing way.

 

In a SET amp, the circuit is really simple. I must add that my SET Tube amp has no global feedback and Tube rectification.

[Ralf11]

While the existence of high 2nd order harmonics isn't a goal of SET, don't they usually have higher levels than other designs?

[YashN]

It's interesting that SET is usually characterized as euphonic, smooth etc. In reality, good SET matched with the right speakers usually sounds quite raw (in the good sense of the word ). And the dynamics of such combo is *brutal*. Believe it or not, everything else will sound vague and anemic once you have a proper experience of SET.

The rendering of attacks by my SET is utterly crazy, and I don't even yet have really highly efficient speakers yet (fortunately, small distance between those and the seating position though, so it's loud enough).

[YashN]

While the existence of high 2nd order harmonics isn't a goal of SET, don't they usually have higher levels than other designs?

Where?

[Keith_W]

Some time ago, I had my Cary CAD-211AE amplifier (110W push-pull) on my engineer's bench to do some repairs. We had a very interesting conversation. It went something like this:

 

Him: "Look at this. The voltage rail on the push part of the circuit measures at 904V. The voltage rail on the pull part of the circuit measures 890V"

 

Me: "You are saying that the push voltage and the pull voltage are different? Will that affect the sound?"

 

Him: "Yes it will"

 

Me: "Why are the push and pull voltages different?"

 

Him: "Because of valves. Most likely the valves on the push side are of a different specification to the pull side"

 

Me: "But they I bought them from the manufacturer as a matched pair!!"

 

Him: "There is no such thing as a matched pair of valves. [He made some complicated point about manufacturing valves and how they might match at some voltages and not others which I did not fully understand]. Also, valves that are matched at one temperature may not match when they are fully heated, and valves will age at different rates, which will affect the voltage."

 

Me: "Do the manufacturers of valve amps know that?"

 

Him: "Of course they do. They can measure it"

 

Me: "Why don't they supply potentiometers so that you can adjust the push and pull side of the amp separately, just like how there is a potentiometer to adjust the bias of this amp?"

 

Him: "Of course that is possible, but you have to look at it from the point of view of the manufacturer. Do you really want to increase complexity for the customer?"

 

Me: "Why would anybody design a push-pull valve amp, knowing that there will be an imbalance between push and pull, due to the fact that valves are variable in nature and are almost impossible to match? Doesn't this mean that all push-pull valve amps are flawed?"

 

Him: "Some engineers design for an ideal world."

 

Me: "What would you design?"

 

Him: "As you say, if I was to design a push-pull valve amp I would have separate bias for push and pull. But for me the ideal amp is a single-end triode"

 

Me: "But they measure horribly"

 

Him: "They measure perfectly fine if you keep them within their linear operating range and don't drive them too hard"

 

Me: "But in the real world, their low output current and high output impedance means that they will be clipping more often than not!"

 

Him: "Correct, so you need to choose your loudspeakers very wisely"

 

Me: "But most of those high sensitivity loudspeakers have problems of their own"

 

Him: "You asked me about amplifiers, not loudspeakers. A SET amp, operating within its linear range, is one of the best amps you can buy. The major problem, as you pointed out, is how to make sure it stays within its linear range ..."

 

I thought that was a nice discussion about the advantages and disadvantages of push/pull vs. SET.

[Ralf11]

Where - usually said to be at higher signal levels

 

I get the impression that SET is not a high power output design (??)

 

Anybody using MOSFETs in this topology?

[YashN]

Him: "You asked me about amplifiers, not loudspeakers. A SET amp, operating within its linear range, is one of the best amps you can buy. The major problem, as you pointed out, is how to make sure it stays within its linear range ..."

 

I thought that was a nice discussion about the advantages and disadvantages of push/pull vs. SET.

Yep, that was great!

[YashN]

Where - usually said to be at higher signal levels

 

I get the impression that SET is not a high power output design (??)

 

Anybody using MOSFETs in this topology?

 

Where are the comparison of the figures?

[YashN]

I get the impression that SET is not a high power output design (??)

 

It doesn't have to be. There are some high-output SETs though.

[Keith_W]

Anybody using MOSFETs in this topology?

 

Yes. Valvet amplifiers have single-ended MOSFET's. I have a pair of Valvet A1R monoblocks.

 

(edit), also Marchand EC626.

[One and a half]

@Ralf11 , here's an objective view, mainly in reply to a Ken Rockwell review of a tube amplifier. The post explains push pull, the distortions with graphs which are in the main from stereophile. How low distortions are, is a matter of degree of course and how much the speakers will work in with a SET.

[astrotoy]

My experience with SETs began 20 years ago in a Hi-Fi shop in Hong Kong, where I was visiting. I was perusing their vinyl bins in the back of the rather small - long and narrow store and there was no one in the store except for me and the owner who was in the front of the store talking to a rather heavy set man, with a woman who was knitting, sitting about half way back. I didn't pay them much attention as I was doing some serious vinyl hunting. All of a sudden music started, and I was gobsmacked! I stopped in my tracks (something I never do when looking for vinyl), and walked up to the front of the store and sat down. I asked whether it was OK and they assented and I was totally amazed at the sound coming from two non descript speakers. It turns out it was the first pair of SET amps that I had ever heard, courtesy of Riccardo Kron (and his wife Eunice) and their KR SET amp, using their new at the time Western Electric 300B model tubes, made in their plant in Czechoslovakia (at the time). I found out how much they cost, and how little power they put out, but I knew I would be looking for a way to get a SET amp and a pair of speakers that could play them.

 

I tried Nelson Pass's Aleph 3 amp, his solid state way to emulate a SET. Finally, 8 years later I saw a pair of Cary 2A3 Signature amps used for a price I could afford. I then found a used pair of Avantgarde Duo's with 103db efficiency was a perfect match for the 3.5w per channel power of the Cary's. That was 13 years ago, and I have the same amps and speakers, with no particular inclination to change. I regularly hear some great speakers and amps that cost more than (Magico Q3, 5, 7, M project, Big Constellation amps, among others) but nothing that has spoken to me like those SET amps. My system has changed quite a bit over the years, but the SET's and matching speakers have been a constant.

 

Larry

[jbparrish]

Very interesting. Being new to high-end audio I went to every single room and listened to every set of speakers at the last audio show here in SF. The one that was absolutely unforgettable was a high-efficiency speaker driven by SET amplifiers. I was smitten. But I was not sure which component I was listening to, the speakers were very very nice, the DAC was world class, and the SET amplifier was very expensive, at least by my standards. I will say that what you are describing here is what I heard. I guess I'll have to look more into it. question though what are the best reasonably priced high efficiency speakers?

 

 

Sent from my iPad using Computer Audiophile

[YashN]

Just be sure as you can that the amp is performing with a speaker that allows it to shine.

Certainly a must. In fact, I am re-building my system around my SET. Going to give it all it needs to shine through the best it can so mostly for the mid-range, and then complement with other equipment where needed.

[YashN]

My experience with SETs began 20 years ago in a Hi-Fi shop in Hong Kong,

 

20 years ago I was visiting Asia, was having some fun at Ocean Park too!

[Panelhead]

I used to think everyone who uses solid state equipment needs a hearing aid. The euphonics were so pleasing.

Once I started to build my own equipment it became very obvious that power supplies are what is important. One person who has proved to design great equipment is Tim De Paracini. He has stated he can get the same results from solid state or tube. But no one will purchase the solid state. So he designs tube gear.

I am now big on equipment that measures well. Whether SS, tube, or a combination. Same with speakers. Linear frequency response and dynamic response are what defines high end audio.

[Ralf11]

@Ralf11 , here's an objective view, mainly in reply to a Ken Rockwell review of a tube amplifier. The post explains push pull, the distortions with graphs which are in the main from stereophile. How low distortions are, is a matter of degree of course and how much the speakers will work in with a SET.

 

did you mean xnor or kreuger?

 

hard to follow that thread...

[TubeLover]

VAC pa 35/35

 

Moth Audio s45

 

 

I went through a coupe of push-pull amps before I settled on a VAC pa 35/35. This is a push-pull 32 watt triode amp with EL-34 output tubes. Also has volume control. Really liked that amp a lot, tweaked it with the best NOS tubes. That was 17 years ago. Then I kept reading about single-ended triodes and decided to sell the VAC and ordered a custom Moth s45 SET [with volume control] that could use either 2A3 or 45 output tubes.

 

Here's a collection of notes I kept in my online listening journal from that period....

 

 

Early Impressions: Moth vs VAC. Let me begin by saying, I enjoy my system MORE with the Moth than I did with the VAC. Even with the compatibility issues of the 2-5wpc Moth+93db Sonatinas I'm willing to live with the hick ups while savoring what the Moth does so right.

 

Perspective: The perspective with the Moth is more recessed, and the images more discrete, than the larger-gestured VAC. One is not better than the other, this is more an issue of preference.

Detail / transparency / naturalness: The Moth wins big-time. There is just more of a rightness that "appears" to convey a more accurate representation. Is it more accurate? I don't know, but it gives a better impression of live instruments in the room - timbrally. Transient speed / micro-dynamics: Again the Moth wins hands down. PRAT is much better, the music propels itself, like actual music-making. The rhythm section is much more connected to the source AND the listener.

 

Space / imaging: The VAC was very special in this regard. I'm still not sure how the Moth measures up. Obviously there is no clear-cut winner. I find the soundstage to extend further from the edge of the speakers with the Moth, and somewhat more dis-embodied from the enclosures in the near-field. But I'm inclined to say the VAC had more of a 3-D effect, where images have more freedom in the room, in the global sense. Sometimes images would appear from behind the listener, then move centre stage, then vacate. I'll have to listen for which outlines venues better, but I would think the VAC is superior in this effect.

One month update: Surprisingly images have increased in both size and perspective. Whereas images were much smaller in relation to the VAC and more recessed in the sound field, now they are more developed and forward, with wrap-a-round effect: Like swimming in sound or being immersed in an ambient dream. 3>. The concerns I had with leanness IMS are pretty much gone. Even with the more analytical 45s I'm satisfied with the realistic sense of body from instruments. The bass from either 2a3 or 45, though having different characteristics, has remained very impressive. The 45 kills the renowned bass performance from the Amperex double-d-getter EL34's, least IMS with the VAC!

 

 

The 45s are spooky in the way they dis-associate themselves from their enclosures. That openness I was referring to. Sounds hang more in space, something that wasn't lacking with the push-push VAC. I find that the lower output of the 45s (I'm speaking of the "ST", not the "Globe" 45) is offset by the incredibly engaging bass and swinging micro-dynamics. That the need for volume is reduced by the more lively sound. This is one of the main attractions of SETs: Enhanced dynamics even with lower volume coupled with greater listening ease which affords longer, more pleasurable sessions. This ease is due to lower output levels and the angelic presentation that is the hallmark of SETs. Imagine pristine smoothness and lighting transients - simultaneously!

 

Three month update. It's been 6 weeks since my last report. Now approaching three months with the amp, this is a good time to address some issues I may have waffled on in previous posts. If unclear, I LOVE THIS AMP! This speaks more of what the Moth does right than a lacking on the part of my old amp. With the prior grouping there was just a nagging feeling that something just wasn't "right" that I attributed to the VAC and now with just this one [1] change, there is a feeling of "rightness" with it. IMS/room, with my music (coupled with my replay preferences), this amp mated to my Sonatinas I could easily live with THIS setup for awhile, * it satisfies - Me!

 

 

* 15 years later I still own it.

 

 

Very well said. Craig makes superb and brilliant amps. I am honored to own one of his ultimate 2a3 headphone amps, (only three were made). Not sure what kind of financing you are finding for the 45's though! Does it involve a first born child?

 

JC

[TubeLover]

Very interesting. Being new to high-end audio I went to every single room and listened to every set of speakers at the last audio show here in SF. The one that was absolutely unforgettable was a high-efficiency speaker driven by SET amplifiers. I was smitten. But I was not sure which component I was listening to, the speakers were very very nice, the DAC was world class, and the SET amplifier was very expensive, at least by my standards. I will say that what you are describing here is what I heard. I guess I'll have to look more into it. question though what are the best reasonably priced high efficiency speakers?

 

 

 

 

Sent from my iPad using Computer Audiophile

 

Clearly your ears are good. The journey you have begun is not remotely inexpensive though, especially regarding speakers. but there are some options. Make that journey! The rewards are unending. Let me know if I can help.

 

JC