SET amp owners thread

[Empirical Audio]

Which amp is that?

Arte Forma "Due Volte"

 

[Ron Resnick]

. . . Compared to my 1000W modded JC-1 monoblocks driving the same speakers, the SET monoblocks beat the SS in every category, highs, bass and slam.

I was open to believing every word, until I got to your last word, "slam."

I don't see how your 35 watt SETs can deliver more "slam" than JC1s.

 

[DaveC]

I was open to believing every word, until I got to your last word, "slam."

I don't see how your 35 watt SETs can deliver more "slam" than JC1s.

SETs relatively high output impedance and (normally) no feedback makes having a speaker with smooth impedance vs frequency important if you want even frequency response. It's common for a speaker to have a dip in the low frequency impedance that will cause a bump in bass response which can be interpreted as more "slam".

SET can also respond very quickly with no zero-crossing distortion issues so I think transients can be heard as being sharper and very precise, which can also be interpreted as having better "slam".

 

[Empirical Audio]

I was open to believing every word, until I got to your last word, "slam."

I don't see how your 35 watt SETs can deliver more "slam" than JC1s.

Efficient speakers I guess. The amps were modded by me, so they have fast decoupling unlike most tube electronics.

 

[Atmasphere]

Big iron = bassballs
if a amp doesn’t hurt when you try to pick it up it’s not an amp... it’s uhhhmmm interior design

The problem in an SET if it really is that heavy, might be because its built in an attempt to make power. Getting over about 7-8 watts is tricky, as its so hard to make bandwidth when you get over that power level. Usually they wind up being bass shy.

 

[Atmasphere]

So, the phase splitter is evil...

Depends on how its executed! This is a common saw, and its not entirely accurate.

The real problem is that most push-pull amps are single-ended combined with push-pull outputs. This results in a bit of 5th harmonic that gives them a certain sound. The only way to avoid this I've found is either go single-ended all the way (and get a 2nd harmonic, based on a quadratic non-linearity) or go fully differential from input to output and get a 3rd harmonic (cubic non-linearity). The ear treats both the 2nd and 3rd the same way- they both contribute to 'warmth', 'body' and the like.

Differential amplifiers make excellent 'phase splitters'.

The difference is that an amp based on a 3rd harmonic will have about 1/10th the distortion at full power and will have overall less higher ordered harmonic distortion, resulting in a smoother and more neutral sound. If not running feedback, it will also have a cleaner 1st watt than an SET, and share with it a linearly decreasing distortion signature as power is decreased to zero. Most push-pull amps have distortion increasing below a certain power level (4-6% or so of full power). It does not seem to matter if that fully differential amplifier is transformer coupled and even if it has interstage transformers, the 3rd harmonic will still be the primary distortion component. I prefer to go transformerless of course

 

[morricab]

Depends on how its executed! This is a common saw, and its not entirely accurate.

The real problem is that most push-pull amps are single-ended combined with push-pull outputs. This results in a bit of 5th harmonic that gives them a certain sound. The only way to avoid this I've found is either go single-ended all the way (and get a 2nd harmonic, based on a quadratic non-linearity) or go fully differential from input to output and get a 3rd harmonic (cubic non-linearity). The ear treats both the 2nd and 3rd the same way- they both contribute to 'warmth', 'body' and the like.

Differential amplifiers make excellent 'phase splitters'.

The difference is that an amp based on a 3rd harmonic will have about 1/10th the distortion at full power and will have overall less higher ordered harmonic distortion, resulting in a smoother and more neutral sound. If not running feedback, it will also have a cleaner 1st watt than an SET, and share with it a linearly decreasing distortion signature as power is decreased to zero. Most push-pull amps have distortion increasing below a certain power level (4-6% or so of full power). It does not seem to matter if that fully differential amplifier is transformer coupled and even if it has interstage transformers, the 3rd harmonic will still be the primary distortion component. I prefer to go transformerless of course

It was my understanding that 2nd order creates a more "open" sound whereas 3rd harmonic is a "hooded" sound. Trumpet, for example, has a lot of 2nd harmonic but Clarinet has more 3rd harmonic, which gives it that "hooded" or more "closed in" sound. One of the best PP tube amps I ever heard was from Vacuumstate, which was fully differential from input to output (It was not OTL though...had nice Lundahl output iron). I don't know if I liked it more than a good SET but it was definitely making good music.

I think you should build a good single ended OTL. Aries Cerat makes one (it is huge and hugely expensive for 20 watts) that I haven't heard yet but hope to one day in the not too distant future. Transcendent Sound makes a budget kit one, which does use feedback (The Aries does not) but I heard one once on some Klipsch Cornwalls and it was really something to hear.

 

[morricab]

The problem in an SET if it really is that heavy, might be because its built in an attempt to make power. Getting over about 7-8 watts is tricky, as its so hard to make bandwidth when you get over that power level. Usually they wind up being bass shy.

If you have big (and good quality) iron the problem is not bass but high frequencies and this then comes down to the quality and technique of the winding. I had a JJ-322, which was quite heavy (42kg) for a parallel 300B amp and it also had quite large (over 10kg each) Double C core output transformers to get a spec'd 20 watts/channel. According to a Polish magazine review (can no longer find it online now sadly) the amp was able to do 15 watts at 1% THD (predominantly 2nd order but then exponentially decaying with increasing order) and a full 20 watts with about 2% THD. Bandwidth was from below 20Hz up to 35Khz at -1db. This amp had very nice bass (on the appropriate speaker), very nice mids but slightly recessed highs (not bad mind you but noticeable against the best SETs I have owned). I often wondered why that was when it was clear the bandwidth was well over 20Khz. Could it have been the winding technique used? Possibly. Still, with an easy speaker it was a very nice sounding amp with low coloration (other than the noted highs).

Contrast that with my Aries Cerat Genus, which is full bandwidth and sounds every bit of it, the highs are open the bass is powerful and the mids like a SET should be. It has significantly bigger iron than the JJ but not recessed highs and even though the iron is not C-core I think the superior winding tech gives this amp the high end bandwidth advantage over the JJ (not to mention it drives effortlessly every speaker we have tried it with...down to 83db Boenicke speakers! The JJ...not so good with average sensitivty speakers). The big core allows neutral, dry but textured (lack of negative feedback helps a lot here I think) and extended bass...a bit like good SS bass but more texture.

 

[Atmasphere]

It was my understanding that 2nd order creates a more "open" sound whereas 3rd harmonic is a "hooded" sound. Trumpet, for example, has a lot of 2nd harmonic but Clarinet has more 3rd harmonic, which gives it that "hooded" or more "closed in" sound. One of the best PP tube amps I ever heard was from Vacuumstate, which was fully differential from input to output (It was not OTL though...had nice Lundahl output iron). I don't know if I liked it more than a good SET but it was definitely making good music.

I think you should build a good single ended OTL. Aries Cerat makes one (it is huge and hugely expensive for 20 watts) that I haven't heard yet but hope to one day in the not too distant future. Transcendent Sound makes a budget kit one, which does use feedback (The Aries does not) but I heard one once on some Klipsch Cornwalls and it was really something to hear.

There is an enormous!! difference between harmonics that are part of instrument timbres and those caused by distortion- in the above post you are conflating the two and it simply doesn't work that way. The ear treats both the 2nd and 3rd harmonic (when it distortion) exactly the same way. The 3rd harmonic is present in SETs at a higher level than it is in a fully differential amplifier; if what you said were true then SETs would be unlistenable as they would sound too 'hooded' and 'closed in'.

The thing about amplifiers is you need bandwidth. If you want the bass to be really right, then you need bandwidth to 1/10th the cutoff frequency- so if 20Hz is desired then you need to go to 2 Hz. Same on the other end- if you want to go to 20KHz you need to go much higher - at least 100KHz. You can see right away that no SET is going to do this. Now you might ask, since many people do, 'why have all that bandwidth if you can't hear it?' and the answer is phase shift. While you can't hear the phase of a sine wave, you can certainly hear phase shift over a frequency spectrum in the form of tonality and soundstage. Get the phase shift right and the amp has a more natural more musical high end, and a deeper wider soundstage. This will also give it the ability to sound faster and more detailed, but in a relaxed way without brightness, since these are also perceptions of low phase shift.

When the filter (which is what an output transformer is) imposes a 6dB/octave rolloff, the phase shift components can be seen to 10x or 1/10th the frequency of the cutoff (IOW the -3dB point) depending on which end of the spectrum the rolloff is located. So a 20KHz -3dB point has audible components down to 2KHz. This has been known a long time; its why the early H/K Citation series had such wide bandwidth. It sounds more real.

We recently repaired a single-ended OTL here in our shop (belonged to a local customer who replaced it with a set of M-60s and then went to MA-1s) and got to compare it to our amps on a benign 16 ohm load. It was a nice sounding amp; the fact that the customer immediately replaced it should tell you what you need to know. This would be entirely anecdotal were it not for that customer placing threads on audiogon about his experiences.

 

[Atmasphere]

I was open to believing every word, until I got to your last word, "slam."

I don't see how your 35 watt SETs can deliver more "slam" than JC1s.

'Slam' has nothing to do with amplifier power, and everything to do with how the amplifier interfaces to the loudspeaker! Since SETs do not employ feedback, they have a higher output impedance and so tend to act as a power source rather than a voltage source. So the kind of speaker that a solid state amp works on will cause an SET to fall flat on its face, but the kind of speaker designed to work with an SET will likely sound horrendous with an amp that acts as a voltage source.

For more on this see:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

A lot of people including degreed engineers often argue the points I make in this paper. I didn't make this stuff up- it is simply because they are for whatever reason (youth?) not grounded in audio history. The Power Paradigm is what was around before the Voltage Paradigm rules were promoted by Mac and EV in the late 1950s, but took over 20 years to take root. Now everyone thinks speakers are 'voltage driven' but obviously that simply isn't the case.

 

[bonzo75]

"So the kind of speaker that a solid state amp works on will cause an SET to fall flat on its face, but the kind of speaker designed to work with an SET will likely sound horrendous with an amp that acts as a voltage source."

Yes. In drivers like Altec, high impedance low damping low watt SETs do much better bass and slam while high watt low impedance high damping SS can choke them.

Using SETs on apogees and acoustats is a joke.

 

[Empirical Audio]

'Slam' has nothing to do with amplifier power, and everything to do with how the amplifier interfaces to the loudspeaker! Since SETs do not employ feedback, they have a higher output impedance and so tend to act as a power source rather than a voltage source. So the kind of speaker that a solid state amp works on will cause an SET to fall flat on its face, but the kind of speaker designed to work with an SET will likely sound horrendous with an amp that acts as a voltage source.

For more on this see:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

A lot of people including degreed engineers often argue the points I make in this paper. I didn't make this stuff up- it is simply because they are for whatever reason (youth?) not grounded in audio history. The Power Paradigm is what was around before the Voltage Paradigm rules were promoted by Mac and EV in the late 1950s, but took over 20 years to take root. Now everyone thinks speakers are 'voltage driven' but obviously that simply isn't the case.

Slam has everything to do with power delivery, di/dt.

 

[microstrip]

(...) A lot of people including degreed engineers often argue the points I make in this paper. I didn't make this stuff up- it is simply because they are for whatever reason (youth?) not grounded in audio history. The Power Paradigm is what was around before the Voltage Paradigm rules were promoted by Mac and EV in the late 1950s, but took over 20 years to take root. Now everyone thinks speakers are 'voltage driven' but obviously that simply isn't the case.

Ralph,

The "power paradigm" is nothing new - the rules of power transfer are studied in basic electronics.

And IMHO some technical people argue your statements simply because they are not clearly and fully explained - you indirectly refer to old papers that are now inaccessible but fail to explain the situation in way people can understand. Creating an aura can be nice for audio forums, but technical people will always want more.

I am not addressing just your OTLs, but it would be nice if designers presented clear technical explanations based in current knowledge about their points. For example, although I now know how you measure the power of your amplifiers, I had to go in several reviews and forums before getting it... IMHO your paradigm page needs some links to the sources you refer. Surely just suggesting, YMMV.

 

[DaveC]

"So the kind of speaker that a solid state amp works on will cause an SET to fall flat on its face, but the kind of speaker designed to work with an SET will likely sound horrendous with an amp that acts as a voltage source."

Yes. In drivers like Altec, high impedance low damping low watt SETs do much better bass and slam while high watt low impedance high damping SS can choke them.

Using SETs on apogees and acoustats is a joke.

Speaker drivers were often overly damped mechanically and depended on the high output impedance of the amp to get proper bass response, so when a low output impedance amp was used there'd far less bass than necessary and it does indeed sound "choked". Modern drivers, even ones intended for SET amp use have gone the opposite direction and have spiders and surrounds that are as flexible as possible, for example AER's ultra-thin foam surrounds, these are more efficient AND work well with most all amplifiers, or at least there isn't that massive difference in performance between SET and SS.

 

[morricab]

There is an enormous!! difference between harmonics that are part of instrument timbres and those caused by distortion- in the above post you are conflating the two and it simply doesn't work that way. The ear treats both the 2nd and 3rd harmonic (when it distortion) exactly the same way. The 3rd harmonic is present in SETs at a higher level than it is in a fully differential amplifier; if what you said were true then SETs would be unlistenable as they would sound too 'hooded' and 'closed in'.

The thing about amplifiers is you need bandwidth. If you want the bass to be really right, then you need bandwidth to 1/10th the cutoff frequency- so if 20Hz is desired then you need to go to 2 Hz. Same on the other end- if you want to go to 20KHz you need to go much higher - at least 100KHz. You can see right away that no SET is going to do this. Now you might ask, since many people do, 'why have all that bandwidth if you can't hear it?' and the answer is phase shift. While you can't hear the phase of a sine wave, you can certainly hear phase shift over a frequency spectrum in the form of tonality and soundstage. Get the phase shift right and the amp has a more natural more musical high end, and a deeper wider soundstage. This will also give it the ability to sound faster and more detailed, but in a relaxed way without brightness, since these are also perceptions of low phase shift.

When the filter (which is what an output transformer is) imposes a 6dB/octave rolloff, the phase shift components can be seen to 10x or 1/10th the frequency of the cutoff (IOW the -3dB point) depending on which end of the spectrum the rolloff is located. So a 20KHz -3dB point has audible components down to 2KHz. This has been known a long time; its why the early H/K Citation series had such wide bandwidth. It sounds more real.

We recently repaired a single-ended OTL here in our shop (belonged to a local customer who replaced it with a set of M-60s and then went to MA-1s) and got to compare it to our amps on a benign 16 ohm load. It was a nice sounding amp; the fact that the customer immediately replaced it should tell you what you need to know. This would be entirely anecdotal were it not for that customer placing threads on audiogon about his experiences.

What you are saying is incorrect Ralph, the fact that a SET might have higher 3rd harmonic than a PP amp is not relevant it is the relationship with the other harmonics that are far relevant (i.e. the pattern of the distortion). This was long ago recognized by engineers in the BBC and later Jean Hiraga that a monotonic harmonic distortion pattern is more pleasing to the ear because that is more typical of what is observed in nature. A PP amp cancels even order harmonics and this is perceived as unnatural.

There was a test performed by Keith Howard that demonstrated, by digitally adding distortion to recordings, that the undistorted recording was best; however, of distortion patterns that typical electronics make the next best sounding to undistorted was a monotonic decay pattern with an exponential decay from 2nd to 3rd to 4th etc. What sounded distinctly worse was an all odd pattern of 3rd, 5th, 7th etc. that is typical of push/pull amps where even harmonics get cancelled. Somewhere in between was an all even pattern of 2nd, 4th 6th etc. which is a highly unlikely pattern to get as there is not an obvious mechanism. This was with all patterns decaying exponentially, which is not the actual case in a lot of amps where the pattern look more like a picket fence out to 20th order.

So, please don't oversimplify the situation with some easy heuristics that 2nd and 3rd are the same as if they are ever in isolation in an amp. The overall pattern is very important (apparently the phase of the harmonics as well, which is not obvious from a FFT spectrum).

 

[bonzo75]

Speaker drivers were often overly damped mechanically and depended on the high output impedance of the amp to get proper bass response, so when a low output impedance amp was used there'd far less bass than necessary and it does indeed sound "choked". Modern drivers, even ones intended for SET amp use have gone the opposite direction and have spiders and surrounds that are as flexible as possible, for example AER's ultra-thin foam surrounds, these are more efficient AND work well with most all amplifiers, or at least there isn't that massive difference in performance between SET and SS.

Yes those speakers were highly damped to go with the amps of those times. Something like an eminence woofer will be the opposite

 

[morricab]

Speaker drivers were often overly damped mechanically and depended on the high output impedance of the amp to get proper bass response, so when a low output impedance amp was used there'd far less bass than necessary and it does indeed sound "choked". Modern drivers, even ones intended for SET amp use have gone the opposite direction and have spiders and surrounds that are as flexible as possible, for example AER's ultra-thin foam surrounds, these are more efficient AND work well with most all amplifiers, or at least there isn't that massive difference in performance between SET and SS.

I have noticed this largely with pro drivers or ultra-high sensitivity cones (as you say AER seem to be an exception). My Supravox 215-2000 are very stiff (doped accordion style surround) and hardly move and with a Qts or only a bit over 0.2 they would likely sound overdamped with SS.

 

[morricab]

Yes those speakers were highly damped to go with the amps of those times. Something like an eminence woofer will be the opposite

Depends completely on the woofer in question (Eminence makes dozens of woofers with wildly different properties) and the box loading.

 

[morricab]

"So the kind of speaker that a solid state amp works on will cause an SET to fall flat on its face, but the kind of speaker designed to work with an SET will likely sound horrendous with an amp that acts as a voltage source."

Yes. In drivers like Altec, high impedance low damping low watt SETs do much better bass and slam while high watt low impedance high damping SS can choke them.

Using SETs on apogees and acoustats is a joke.

Your opinion is just that and not a fact (fact is that it works well) but you should stay away from any thread that is even hinting at a technical discussion.

 

[bonzo75]

Your opinion is just that and not a fact (fact is that it works well) but you should stay away from any thread that is even hinting at a technical discussion.

I am not discussing technically at all. You should stay away from one that brings out the fact you can't listen to acoustats and apogees clipping with SETs