[les24preludes]

I've been building tube amps and preamps for 10 years on a recreational basis. I'm a musician and so I'm very familiar with live acoustic sounds - the orchestra, jazz combos, singers of all types. My priorities are simple:
1. Timbre. The reproduced sound must be uncannily close to the acoustic sound. Clarinets must sound woody, cymbals must shimmer, snares must have a snap and toms a round boing, a Steinway must sound like a Steinway and not a Bechstein. I check all builds on acoustic instruments and the reality in the sound should be thrilling.
2. Detail and clarity. Orchestral textures must be transparent, tiny details in the mix should be audible, lyrics should be clear. You can check low level details to see if they ae there or not.

I started off using the usual indirectly heated tube range like EL84s, 12A*7s, but my jaw dropped in astonishment when I first heard a 26 directly heated triode. So from 2010 I only built with directly heated triodes or DHTs. Think tubes like 300b, 2a3, 45. These had more clarity and uncannily realistic timbre. Like a veil had lifted.

So where is "warm" in this? Short answer, it isn't. And especially the myth that "warm" can imply a lack of clarity and detail. But the term I'd suggest is "smooth". Solid state can sound slightly edgy and dry unless done really well, while tubes can generically be smoother and fuller in sound. Probably a lot to do with the harmonic spectrum and the distribution of even and odd harmonics.

I can't comment on soundstage since this doesn't really interest me, though it's important to others. As above, it's all about timbre and clarity. That's what I get from tubes, and specially DHTs.

 

[Oddiofyl]

When people say "warm " sounding do they mean the upper registers are rolled off? Not sure, but I would like to point out that an amp like the Quicksilver is full bodied for lack of a better word. The timbre is spot on, there is what seems like effortless high frequency extension but it is never harsh or "bright".

 

[Aanta]

When people say "warm " sounding do they mean the upper registers are rolled off?

In my case absolutely not.
When I say warmth it is to describe a bump in the upper part of the bass range.
It sound pleasant to the ear, but is not really good Hifi.
Whereas some seem to use the term for muted transients in the bass range - which I do not find preferable at all.

From your description the Quicksilver sound very nice.

So I like warm tubes, meaning they give a bit of bass boost in one headphone amp that have no tone controls.
The ideal tube should at the same time also have the clarity in the higher range described by les24preludes above.
I got a very small set of tubes that satisfy those requirements, sadly I do not have such for all positions needed.
These are not from Europe or USA, but actually Japanese - Matsushita and I know the background why they sound the way they do.
Back then there were actually a human tester, who listened in headphones to every single tube they produced.

Many audio tubes are good for frequencies up to 30KHz while 6V6 Go up in the megahurtz range, we cannot hear the latter of course.
Over the years I have noted that many audiophiles have an extended hearing range that go higher than for the average person.
I used to have that myself but while I am getting older, I have lost the hearing that once did reach 22KHz.
But I am still able to hear a difference, I think the extended range helps in getting harmonic overtones.

 

[audiojan]

I would say not necessarily, just like a solid state amp can't be warm. My experience with headphones is slightly limited so I'll draw my examples from the hifi area instead... Think about a Pass Labs class A amp (XA25, XA30., XA60., etc) and they can be extremely "tube like", where as some of the VTL tube amps can sound "solid state like". It all comes down to the design/designer and the profile target.

 

[les24preludes]

Nelson Pass is a very interesting guy to bring up here. His aim was to make solid state sound as good as a triode vacuum tube. He actually commissioned special solid state devices that worked like triodes and made a SE single ended amp with them, using monster heatsinks. And on the other hand OTL tube amps (output transformer-less) can sound cleaner because they don't have an output transformer. With tubes you are usually listening to a transformer somewhere in the signal path, and that has its own sound. Though with headphone amps it's possible to use circuits that don't need a transformer and lower the impedance with tubes themselves or solid state devices or a combination.

 

[Tarttett]

I've owned solid-state amps which are similar in fullness but never one with the recording independent depth factor.

Which amps did you own which were similar in fullness to tube amps, and what do you think they had that other solid-state amps did not that gave them that fullness?

 

[Tarttett]

I've seen it said that tube amps "tend" to distort in even-order harmonics while solid-state amps "tend" to distort in odd-order harmonics. Is it an inherent function of the technologies, or can tube amps distort in odd-order harmonics, and solid-state amps in even-order harmonics as well?

 

[MohawkUS]

Which amps did you own which were similar in fullness to tube amps, and what do you think they had that other solid-state amps did not that gave them that fullness?

Anything vintage I've owned(ex. Sherwood S6000/8600,) Burson 160DS, Schiit Asgard 3. The Phonitor e even does it to a degree although it isn't warm like the others. There really isn't much in common between these amps & none of them will fool you into thinking you're listening to a tube amp. I don't have a theory on why they sound as they do.

To answer your question on harmonics, it's more complicated than that. There are amps which will be even ordered at one power output & odd dominated at another. Comparisons between amps are only useful if you assume the same headphone and volume. It's difficult to point to an amp and place it exclusively into a category regarding its distortion charismatics unless it was specifically designed to be consistent in its distortion profile.(Thinking some Nelson Pass designs & hybrid type amps where the tube sees a predictable load. These types of amps have a deliberately tuned distortion in the pre/buffer stage and a clean power stage to reduce variability.) The other exception would be amps so clean in pre/power stages as to have imperceptible distortion in all possible usage scenarios.