Is tube "compression" a thing when pushing tube amps?

[JSQT]

So I listen to my 25Wpc Luxman tube amp about 9 feet away from my speakers. Speakers are roughly 98-100dB efficient. If I am playing "loud" I am measuring about 90-95ish dB on my SPL meter from my listening position. Normal nighttime listening is closer to 80-85.

By doing the math, it looks like at the highest sound levels, I'm pushing maybe 4 watts from the Luxman tube amp. This is around 11 o'clock on the preamp dial FWIW. Normal listening is a hair under 9 o'clock.

However when I had my speakers delivered and I was checking them out at about SPLs in the mid-90s, Greg the speaker designer was with me and he was saying he could definitely hear "tube compression" from the amp being pushed. I did notice the sound was not as smooth at the higher volume. But I'm figuring - by doing the math - again it's maybe 4 watts tops and these tubes should not be reaching any limitation at that level. Greg estimated from what he was hearing I had to be pushing more than 10 watts. But the math doesn't add up to be using up that much power.

So I guess my question is - is it normal to hear a bit of tube breakup or compression at 3-4 watts on a 25Wpc tube amplifier? If it matters, the Luxman is a push-pull triode.

I do have another MQ-88uSE arriving tomorrow and I am going to run them in mono configuration, so that may open up a little more headroom. I'm not sure what to expect fidelity-wise.

[bluegrassphile]

I can only speak to tube guitar amps. And, yes, there is tube compression. But with guitar amps it's often desirable. In home audio amps it's desirable only in certain circumstances. Something called 2nd order harmonics is one factor that comes into play. However, I am now into this discussion over my head, so someone more knowledgeable than myself will have to take it from here.

[mulveling]

I used to use vintage (restored) 25 Watts/ch and 35 Watts/ch tube monoblocks (KT66/7581A and EL34, respectively) on a set of 93 dB/Watt, 8 ohm Tannoy Kensington SE. Note that 100 Watts/ch on 93dB/Watt would be analogous to 25 Watts/ch on 99 dB/Watt speakers. My typical listening levels are similar to your "loud" levels, and include a lot of hard rock & heavy metal. It sounded very good overall, but I noticed I could edge into hard clipping on occasion, and wanted to put a quick stop to that! Clearly, more power was warranted, but how much? I heard a BIG cleanup to the sound - improved dynamics and clarity along with a complete absence of clipping - after moving to a 65 Watts/ch Rogue Atlas (EL34 tubes, non-Magnum). I was addicted! And I noticed a further expansion of dynamics and additional cleanup (though not quite as significant as the 1st jump) when moving from that 65 Watts/ch to the 90 Watts/ch of a Rogue Stereo 90 amp w/ KT90 tubes (and this is roughly where you currently sit, power-wise, for your more sensitive speakers). And then I noted even further improvements (but again, diminished in magnitude from the prior step) when going from that Stereo 90 to the 275-ish Watts/ch Rogue Apollo monoblocks (first KT90, then KT120).

That was my experience moving up a line from the same maker (Rogue). Of course, if you simultaneously upgrade power brackets AND move to a different maker/lineup, you will be mixing results. E.g. I'm currently "downsizing" to the 200 Watts/ch of VAC 200iQ monoblocks (KT88), because they have more midrange magic and actually sound a bit more powerful & dynamic, subjectively. So I'd guesstimate you're looking at least at 50 Watts/ch range, before any additional power headroom turns into diminishing returns. That +3dB doesn't sound like a "lot", but it can make all the difference in a fine system such as yours. But as always, YMMV

[JSQT]

I used to use vintage (restored) 25 Watts/ch and 35 Watts/ch tube monoblocks (KT66/7581A and EL34, respectively) on a set of 93 dB/Watt, 8 ohm Tannoy Kensington SE. Note that 100 Watts/ch on 93dB/Watt would be analogous to 25 Watts/ch on 99 dB/Watt speakers. My typical listening levels are similar to your "loud" levels, and include a lot of hard rock & heavy metal. It sounded very good overall, but I noticed I could edge into hard clipping on occasion, and wanted to put a quick stop to that! Clearly, more power was warranted, but how much? I heard a BIG cleanup to the sound - improved dynamics and clarity along with a complete absence of clipping - after moving to a 65 Watts/ch Rogue Atlas (EL34 tubes, non-Magnum). I was addicted! And I noticed a further expansion of dynamics and additional cleanup (though not quite as significant as the 1st jump) when moving from that 65 Watts/ch to the 90 Watts/ch of a Rogue Stereo 90 amp w/ KT90 tubes (and this is roughly where you currently sit, power-wise, for your more sensitive speakers). And then I noted even further improvements (but again, diminished in magnitude from the prior step) when going from that Stereo 90 to the 275-ish Watts/ch Rogue Apollo monoblocks (first KT90, then KT120).

That was my experience moving up a line from the same maker (Rogue). Of course, if you simultaneously upgrade power brackets AND move to a different maker/lineup, you will be mixing results. E.g. I'm currently "downsizing" to the 200 Watts/ch of VAC 200iQ monoblocks (KT88), because they have more midrange magic and actually sound a bit more powerful & dynamic, subjectively. So I'd guesstimate you're looking at least at 50 Watts/ch range, before any additional power headroom turns into diminishing returns. That +3dB doesn't sound like a "lot", but it can make all the difference in a fine system such as yours. But as always, YMMV

Thanks! I am hoping that doubling the MQ-88uSE's will give me a lot more headroom, I guess essentially 50Wpc but I'm not sure how the math works out with bridging the stereo amps to mono. I'll know more over the weekend.

I'm kind of stuck (happily so) in the Luxman ecosystem, it's just a brand I love most everything about and the 88uSE sounds positively magical with the KT-88s. I wouldn't say I've noticed any clipping at all, more so a slight constriction in the dynamics of the sound at the louder levels. Speaking of Rogue, I do have a Cronos Magnum II integrated in my office system with the KT120s. I would say the Rogue is a mixed bag for me... Very powerful, dynamic, and rich sound which I love. However I've noticed they are prone to noise (I have a constant hum no matter what speakers I use or where I place the amp - it disappears when music plays), and the CMII at least is nowhere near as transparent and detailed as the MQ-88uSE. It's a very good integrated though especially for the price.

I'm looking forward to seeing what doubling up the Luxmans sounds like and seeing if it opens up that top end when I start to push it!

[mulveling]

I'd love to hear a top modern Luxman someday! Beautiful amps. Yes, you've hit on my big rub with Rogue Audio, across their line. Felt like I was always dealing with some kind of stray ground buzz/hum, if not tube rush from too much gain. Their strength is the dynamic, robust and even "fun" sound as you noted. Certainly, the VACs are on a different plane of refined magic.

[Spock]

... my question is - is it normal to hear a bit of tube breakup or compression at 3-4 watts on a 25Wpc tube amplifier?

In my opinion the problem is precisely when you (like me) pursuit some realistic spl...
That´s what i already said here.

Tubed Power Amplifiers. Are the disadvantages too great ?

Many years ago I had one, but from a certain point on, I started looking for the realism of reproduction,
So I went in search of power, and turned to the SS.
…I always notice some distortion / compression in the sound of the valves.

[Shadowfax]

Speaking about the Rogue Cronus Magnum, the shop I was at recently had one, not hooked up. I was checking out the Luxman 505. He also had Hegel, not hooked up. The guy said he felt that the Rogue was the most Solid State sounding Tube amp he sold while the Luxman Integrateds were the most Tube sounding SS units he sold. I never have had a chance to hear the Rogue so wondering how true his observations are.

[mulveling]

Speaking about the Rogue Cronus Magnum, the shop I was at recently had one, not hooked up. I was checking out the Luxman 505. He also had Hegel, not hooked up. The guy said he felt that the Rogue was the most Solid State sounding Tube amp he sold while the Luxman Integrateds were the most Tube sounding SS units he sold. I never have had a chance to hear the Rogue so wondering how true his observations are.

They tend to be voiced that way with the stock tubes. Especially in the days when they shipped with Electro Harmonix small signal tubes, and EH KT90 power tubes. Judicious tube rolling (especially NOS small signal tubes, Tung Sol KT120, etc) can take things a long way and yield a much better balance. Still not going to sound quite like a VAC at the top of its game, though. And VACs sound like they do out of the box before any tube rolling - amazing voicing work at the factory.

[Kuoppis]

I can only speak to tube guitar amps. And, yes, there is tube compression. But with guitar amps it's often desirable. In home audio amps it's desirable only in certain circumstances. Something called 2nd order harmonics is one factor that comes into play. However, I am now into this discussion over my head, so someone more knowledgeable than myself will have to take it from here.

Another cathode follower guy on the forum, I see .


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[Kuoppis]

Even if tube amps can put out the SPL, they typically do it at factor >10 higher distortion, compared to SS amps. This is what you hear. Distortion increases already from low watt output onwards, and does not require the amp to be anywhere close to its power limit.


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[JSQT]

Speaking about the Rogue Cronus Magnum, the shop I was at recently had one, not hooked up. I was checking out the Luxman 505. He also had Hegel, not hooked up. The guy said he felt that the Rogue was the most Solid State sounding Tube amp he sold while the Luxman Integrateds were the most Tube sounding SS units he sold. I never have had a chance to hear the Rogue so wondering how true his observations are.

Since I work from home on Fridays I just fired my CM2 up this morning and sure enough, it sounds like I just turned on a white noise generator or something. Not sure why these things have such a rep for noise. However once the Chick Corea Trio started playing the noise is imperceptible. I will say with the Tung Sol KT120s and Mazda Cifte tubes though this amp does not sound very solid state at all. Very deep soundstage, great projection and space between the notes. Fat, rich bottom end. Not a delicate sound at all though. Perceptible distortion around the notes.

[mulveling]

Mazda 12AX7 silver plates are by far my favorite tubes in the Rogue Apollo (and Dark version) amps and Ares phono - with Telefunken 12AX7 (smooth or ribbed) coming in a distant second. I hear the gray plate 12AU7 are also excellent (I have the 6189/12AU7 silver plates and they are good), but I preferred Sylvania black plate 12BH7 or RCA 12BH7 black plates to 12AU7.

[atmasphere]

What we are talking about here is how graceful the amplifier overloads. The more graceful, the more it will simply seem to be compressing the sound. But push it a little bit harder and the distortion will become more apparent. Feedback helps reduce distortion, but it also makes for a less graceful overload character.

To this end triode amps will have a more graceful character than tetrode or pentode, as they often run little or no feedback at all.

[Kingrex]

I have 60 watt kt88 tube amps pushing Pure Audio Project Trio 15 with horn that are about 94 to 96 db. I don't think I ever run into compression issues. Even when Eultrafast is here making me turn it up louder than I usually do. What do you think Ed. You hear any compression.

I tell you what. May sound like bull, but since putting the Add-Power in, I have way better overhead and ease in the performance of my setup. It was pretty big change. Some of what you may perceive as compression is not because the amp has issues, but your power delivery system has issues giving the amps what they need. Spend the $425 and get the Symphony and 1 Electraclear. Then make some decisions.

I also love my Ampsandsound Casablanca. I feel they would give VAC Phi200 a run all day. I had a Phi160 integrated here and mine are quite a bit better, IMO. $4500 for a pair (monoblocks).

[JSQT]

I got the 2nd MQ-88uSE in yesterday and they are now fully bridged and running as monoblocks. When listening for the first time last night, I did not hear any of the same compression - totally smooth sound with amazing separation. I will say it's very likely I am not hearing 100% of what the amps are capable of since one amp has about 300 hours on it and the other is brand-new and needs at least 50 hours of break in. If anything right now, the tone is a little "dead" compared to what I am used to. For example, on recordings with well-recorded acoustic guitar, they kind of sound like they need new strings.

I'm going to run it through the weekend and I'm sure the sound will open up.

Also I am not noticing an increase in volume/gain from running the 2 amps. I'm not sure how bridging the amps has affected the output of both amps. The 88uSE has only 1 pair of 8ohm speaker taps. So by bridging them I think I am bringing the output down to 4 ohms. The Rivals are 6 ohm speakers so I wonder if that means I'm getting roughly the same output as I would if I was running a single amp in stereo.

Despite not seeing an increase in volume, I am noticing a increase in "power" if that makes sense. The sound levels are not necessarily louder, but the sound overall is more powerful, the bass has much more meat and presence etc.

I'll update my system pics post sometime this weekend with some new pics and impressions.