Is There Such Thing As The Tube Sound? - BSFEEChannel #21

[bsfeechannel]

TL;DW yes.

This video was inspired by "EEVblog #837 – Reverse Engineering A Valve Headphone Amplifier".


There, and in the respective discussion here in the forum, some argued that the tubes were "doing nothing" since they were connected as cathode followers in the signal path. Others argued that the tubes add a characteristic distortion just the same.

I don't want to rekindle that discussion, but I was curious and decided to investigate. Instead of using pentodes like in the aforementioned video, I used triodes in the condition of heavy distortion, as is common with guitar amplifiers. I used the first two preamp stages of the classic Fender "Tweed" Deluxe 5E3 amp circuit as a reference. Using an audio signal generator and an oscilloscope I found very interesting things about the behavior of tubes and their relationship with other components. It's like firing up a steam locomotive. Their golden age is long gone but they are just fascinating devices.

[Brumby]

There are at least two very disparate applications - the audiophile and the guitarist.  I, too, will not take part in any audiophile discussions - but guitarists are a breed unto themselves....

Some years back, I had an encounter with a guitarist that was a fan of Marshall.  He made concerted efforts to educate me about the Marshall "tone".  Eventually I was able to pick up on the affectation of the sound when the signal was run into distortion - as processed through a Marshall amp.  I finally could appreciate the "tone".  Even to this day, more than 30 years later, I can still pick it.  Other amplifiers have their own characteristic sound - and these become as distinct in guitar circles as a clarinet, flute and french horn would be in an orchestra.

For guitarists, the answer to your question is "yes" and it will differ between brands.

[chris_leyson]

For guitarists, the answer to your question is "yes" and it will differ between brands

I used to work alongside a good guitarist and it's true different amplifiers will produce subtly different sounds. Some Peavey amplifiers use the output transformer B/H loop to generate distortion.

[bsfeechannel]

Other amplifiers have their own characteristic sound - and these become as distinct in guitar circles as a clarinet, flute and french horn would be in an orchestra.

No doubt a guitar amplifier is part of the instrument, but my point was to try to correlate things both audiophiles and guitar players say about tubes. They say things like tube amps are "more open and spacious", "round and dynamic", "super crisp", "organic", with lots of "bite, chime and presence".

In my video I think I managed to decipher at least two of those attributes: "round and dynamic". In fact, the transition from a linear to a non-linear transfer curve on a triode class A amplifier is very gradual (round), and (most astonishingly to me) the transfer curve under distortion changes its shape with the level of the input (dynamic). This is because the tube changes its operating point, as the input coupling capacitor gets negatively charged by the forward conduction of the grid.

Why this may be important? Well, tubes sound great, but they are bulky, fragile, power hungry, expensive. Although tube amp modeling is an activity that's been going on for decades now, I thought I'd investigate it myself. The effect I described above is not trivial to reproduce with analog solid state, I guess. Maybe with DSP.

This is just a tiny aspect. As I stated in the video, I do not believe that just a single tube is capable of giving back the "tube sound". It is a result of a lot of factors. The thumbnail is there to prove. Chet is in his home recording studio. The audio is not only intended to be reproduced using tubes. It's being recorded using tubes. Everything there is tubey and analog. I even think his striped cardigan has something to do with the sound. But that would be the subject for another video.

[b_force]

The problem in these discussions is that people don't seem to understand the whole picture and that certain words and explanations are a big taboo.

The interesting yet difficult part with audio is that there is actually a lot of psychological science involved.
Something that isn't very popular or even respected by many tech engineers.
I can suggest many books with great repeatable experiments done on how humans hear.
But to make a long story short, it's basically totally comparable with tasting food.
This means that if the person in question is convinced about something (even if it's not there) he will experience it.
Great territory for the marketing department to come up with some very juicy made up stories.
Some of these mythical stories are actually so strong that there are quite some engineers out there that started to believe their own success fairy tales.
All objective research seems to be thrown over board.

That on itself is not a big deal. But for some reason people get all very emotional in related discussions about it.

If you know a thing or two about control theory and equivalent circuit theory it is possible to 100% replicate a tube circuit with solid state or something like a DSP.
In that case everything IS (as a fact) 100% identical.

This actually also what's happening in the guitar industry.
People finally see that so called moddeling amps can sound great as well and have a lot of other advantages.

[IanMacdonald]

Guitarists do have genuine reasons to prefer tube amps. Probably the main one is the much larger headroom of the preamp - with a 90v to 180v supply, it can accommodate much louder crescendos without distortion. That, and when it does overload, the effect is not so harsh.

Other reason is robustness - although tubes wear out eventually, transistors tend to die a sudden death, usually as a result of a speaker cable short.    Sudden death of an amp on stage can be embarrassing and costly, especially if the tickets have to be refunded.  Whilst it is perfectly possible to protect a sold state amp against shorts, few manufacturers seem to include any reliable protection. I sometimes wonder if the reason is that they see s/c failures as increasing the sales of replacements. 

To my way of thinking, if a transistor amp can't survive having a screwdriver jammed across the speaker terminals whilst playing loud, then it is not fit for professional use. (Don't try this, in most cases the result will be smoke and empty pockets.) 

[bsfeechannel]

Sudden death of an amp on stage can be embarrassing and costly, especially if the tickets have to be refunded.

Been there. Bought the T-shirt. It's not embarrassing. It's overwhelmingly despairing.