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How is "tube sound" even audible in modern headphone amps? - Page 3

post #31 of 366
Quote:
Originally Posted by madwolfa View Post


I'm not rebutting the fact they distort nicely. But how does that matter when distortion levels are several orders below audible?

 

 

Quote:
Originally Posted by mironathetin View Post
 

don't ask, read!

So you prefer listening to amps that are driven into their nonlinear region? Isn't that something we want to avoid?

The article has some misleading and inaacurate statements. One example is below:

Tubes: "Wider dynamic range than typical transistor circuits, thanks to higher operating voltages"

Tubes are noiser than solid state which lowers a tube amp's DR.. Many modern SS amps have high voltage rails. High voltage rails are not so important for low impedance headphones. You only need so much voltage, any more is wasted.

post #32 of 366
Quote:
Originally Posted by madwolfa View Post
 

I've been looking at Schiit Valhalla 2 specs and this is what puzzles me: how is it even possible to hear the "tube sound" with current crop of super-low noise/distortion/output impedance OTL headphone amps? Which is a great engineering feat by itself, but if the alleged "tube sound" is produced by certain harmonic distortions, how is it even audible with measured THD figures being so low?

 

I'm writing this in "Sound Science" as the similar question in the main forum produced a ton of over-emotional and less so informative feedback, if you know what I mean. Many people got simply upset. And it was kind of expected, but I honestly didn't want to troll... Subjectivist crowd is very sensitive.

 

 

 

"Tube sound" is an ill-defined concept. Often it is associated with strongly dominating second harmonic. This comes more from the topology used than from simply using tubes. As an amusing exercise, one could compare what's happening in between fig.3, fig.6 and fig.11 in this link about the Morgan-Jones tube amp. We start with an amp with strong H2. Then, balancing the White cathode follower output stage to work more like push-pull, H2 and H3 get to similar levels. Then, introducing some feedback, we reduce H2 a lot, H3 becoming the dominating harmonics. Obviously, in this example, the thd levels here are quite high.

 

From the explanations on Schiit's website, the Valhalla uses feedback to achieve those specs. It also uses a White cathode follower, probably correctly balanced. So, even if it had higher thd, it probably wouldn't have the "tube sound" anyway. Schiit themselves claim that it doesn't have the typical tube sound.

 

 

I designed and built some tubes headphones amp myself. Some were tubey, some weren't. It's all down to topology. But tubes are easier to use than most solid state devices in some topologies (low thd open-loop gain stage for example).

post #33 of 366
Quote:
Originally Posted by 00940 View Post
 

 

"Tube sound" is an ill-defined concept. Often it is associated with strongly dominating second harmonic. This comes more from the topology used than from simply using tubes. As an amusing exercise, one could compare what's happening in between fig.3, fig.6 and fig.11 in this link about the Morgan-Jones tube amp. We start with an amp with strong H2. Then, balancing the White cathode follower output stage to work more like push-pull, H2 and H3 get to similar levels. Then, introducing some feedback, we reduce H2 a lot, H3 becoming the dominating harmonics. Obviously, in this example, the thd levels here are quite high.

 

From the explanations on Schiit's website, the Valhalla uses feedback to achieve those specs. It also uses a White cathode follower, probably correctly balanced. So, even if it had higher thd, it probably wouldn't have the "tube sound" anyway. Schiit themselves claim that it doesn't have the typical tube sound.

 

 

I designed and built some tubes headphones amp myself. Some were tubey, some weren't. It's all down to topology. But tubes are easier to use than most solid state devices in some topologies (low thd open-loop gain stage for example).

The only thing is that one has to design the amp to create the 2nd harmonic at a level that is percievable. The below spec is from the Schiit site for the Valhalla 2. That's pretty clean, perhaps clean enough not to hear any distortion, typical typical tube sound or otherwise. By the way, I like clean.

"THD: < 0.04%, 20Hz-20KHz, at 1V RMS, high gain (worst case)"

I've noticed that the better and more expensive tube amps are very clean.

post #34 of 366
Quote:
Originally Posted by StanD View Post
 

"THD: < 0.04%, 20Hz-20KHz, at 1V RMS, high gain (worst case)"

 

 

How does that transform to sound perception?

0.04% THD should translate to roughly 68DB. My amp has 0.1% (worst case), 0.03% (typical - whatever 'typical' means). 0.1% means 60DB. 

 

Both of these values are certainly not consciously audible. But the ear can hear them. What that means for sound perception is then beyond measurement, I guess. For my taste, compared to transistor amps, my tube amp sounds a little tubey, although, 60 DB less than the desired signal is not exactly loud. If that is imagination or perception, who can say this.

post #35 of 366
Modern tube amps can be completely transparent, as BigShot said. But most tubes are designed to give that distorted, euphoric sound that everyone liked in vintage equipment. Expensive vintage equipment sounds much more natural and is much less distorted than lower end vintage equipment because they could design the circuitry properly given enough money. This is why people love tube amps so much, it either reminds them of the past (like owners of classic cars that could easily buy a newer, faster and more efficient model) or they think the distortion makes it sound more realistic compared to low-end "bright and cold" solid state. Now distortion is less of a problem and affordable tube amps costing only slightly more than solid state can sound neutral, but people like the distortion. Like how some people buy unnatural sounding equipment because they suit their preference (like my HE-400) rather than measure neutral. Of course, having at least one natural sounding setup should be everyone's goal (my speakers).
post #36 of 366
Quote:
Originally Posted by mironathetin View Post
 

 

How does that transform to sound perception?

0.04% THD should translate to roughly 68DB. My amp has 0.1% (worst case), 0.03% (typical - whatever 'typical' means). 0.1% means 60DB. 

 

Both of these values are certainly not consciously audible. But the ear can hear them. What that means for sound perception is then beyond measurement, I guess. For my taste, compared to transistor amps, my tube amp sounds a little tubey, although, 60 DB less than the desired signal is not exactly loud. If that is imagination or perception, who can say this.

IMO, at 0.04%, I'd vote for imagination. 0.1% might be percievable. In the end, I prefer low distortion.

post #37 of 366

Something important to remember when speaking about "tube sound": in the speakers world, it has a lot to do with the output transformers limitations. In the headphones world, either the transformers can be made much better or we can use OTL easily. 

post #38 of 366
Thread Starter 
Quote:
Originally Posted by 00940 View Post
 

Something important to remember when speaking about "tube sound": in the speakers world, it has a lot to do with the output transformers limitations. In the headphones world, either the transformers can be made much better or we can use OTL easily. 

 

That's why I was very specific in my OP about the headphone tube amps.

 

I understand that speaker amps impose completely different set of challenges due to higher power requirements and nature of the load (high current/low impedance).


Edited by madwolfa - 6/13/14 at 8:41am
post #39 of 366
Well honestly, headphone tube amps are designed to sound distorted because people like it. It's sort of like how people buy thousand dollar speaker tube amps from McIntosh and Jolida to purposely get the warm mid-range that vintage tube amps gave... except these good tube amps don't mask detail and sound like crap like the low end vintage ones did tongue.gif.
post #40 of 366
Thread Starter 
Quote:
Originally Posted by ToddTheMetalGod View Post

Well honestly, headphone tube amps are designed to sound distorted because people like it.

 

Well, obviously Schiit tube amps were designed with something else in mind - put the lowest distortion possible. People are still buying them for a "tube sound", though.

Which doesn't make sense to me (not the tube sound itself, but the idea of getting it from something with THD in low 0.01s of %).

post #41 of 366
Quote:
Originally Posted by madwolfa View Post

Well, obviously Schiit tube amps were designed with something else in mind - put the lowest distortion possible. People are still buying them for a "tube sound", though.
Which doesn't make sense to me (not the tube sound itself, but the idea of getting it from something with THD in low 0.01s of %).
I was just talking in general, I know some companies such as Schiit design proper, low distortion tube amps. Most people plug in warm, euphoric tubes anyway rolleyes.gif. I guess it is their choice though, but I personally think it would be easier in most cases to switch headphones.

The only time I could warrant using a warm, euphoric tube amp would be with a really good, but bright/thin sounding transducer... such as the HD800. Since the spatial capabilities of that headphone are rare, using a tube amp to counteract its bad qualities makes sense. Also it has a high impedance, so OTL tube amps naturally excel with it compared to solid state.
post #42 of 366
Thread Starter 
Quote:
Originally Posted by ToddTheMetalGod View Post

I was just talking in general, I know some companies such as Schiit design proper, low distortion tube amps. Most people plug in warm, euphoric tubes anyway rolleyes.gif

 

Hmm.. I had an impression tube rolling has little to no effect in any proper (low distortion) amplifier design, since it's a matter of topology, not the specific tube choice.

As long as you're using the same tube type and amplifier remains within the designed operating limits.

 

Or people just put some really bad, dying tubes pulled from some old TVs. That would have an effect, I believe....


Edited by madwolfa - 6/13/14 at 12:38pm
post #43 of 366
Quote:
Originally Posted by madwolfa View Post
 

 

Hmm.. I had an impression tube rolling has little to no effect in any proper (low distortion) amplifier design, since it's a matter of topology, not the specific tube choice.

As long as you're using the same tube type and amplifier remains within the designed operating limits.

 

Or people just put some really bad, dying tubes pulled from some old TVs. That would have an effect, I believe....

 

With the kind of feedback Schiit uses, tuberolling will have no effect if the tubes are roughly similar.

 

 

However, the amount of feedback available changes with the µ factor of the input tube. Due to the wide tolerance of tubes, it might be possible that a new tube with particularly low µ for its kind could significantly alter the feedback (and thus the output impedance).  THD will go seriously up if the same tube also had mismatched sections and if the Valhala is used in high gain mode. I'm too lazy to do the maths with real world figures or to sim a similar amp to see if this would bring it in the audible category. I wouldn't worry about it too much though.

post #44 of 366
Well I guess I don't know as much about tube amps as I thought. What do so many people have against them then? If they're properly designed and people like the sound they have, so be it. They're definitely great for high impedance headphones. In the speaker world I can understand with tough impedance curves requiring a lot of current that people would naturally choose solid state (or high end tubes with 8 ohm speakers).

Perhaps it's the same as people thinking solid state amps are bright, thin, and harsh. People have a stereotype against tube amps thinking they're rolled off, euphoric, and warm.
post #45 of 366

Tubes change as they get older. Even if you liked the sound and it was neutral early on, that doesn't mean it will still be that way a little ways down the road.

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