Tube Amplifier Sound Characteristics

a lot of the main points have been covered here already in the responses to the op’s post

i would add the following...

-- top tube and ss amps converging does not mean they are fully converged to sound the same
-- audio research, for the last 15-20 years at least, has tried to give users their cake and let them eat it too... meaning tubey goodness in holography and tonal accuracy and body, with extended treble and bass depth and impact of good ss...  the ref 75 is an excellent example of them largely succeeding at this endeavor for many applications
-- that said, depending on speaker load, room and volume level desired, how close a ref 75 or 110 comes to say, a top gryphon or pass or hegel in bass response, or how close those ss counterparts come to the arc tube amps in imaging and fleshed out vocals can still be quite variable

@blindjim your description is perfect. Although it may be difficult to put into words I find that when you get to a certain level of performance you are seeking something that is emotionally involving. I remember putting several different SS amps in my system and they all sounded ok. But then I put in a vacuum tube amp and WOW everything just fell into place. It sounded so right in almost every way. For me it wasn't even close. Since then I have tried 3 different tube amps and all sounded better to some degree than the SS amps and 2 were very good. An important note is that the tube amps I demoed were entry level I can only imagine what the "better" units sound like. Amps on the very short list are ARC Ref75SE and QS Mono 120.

@ avanti1960

It surprises me that people still talk mainly in terms of tonal balance when discussing tube amps. The warm, rolled off tube sound as it were. Forget about it! It isn’t what you want anyway. Modern tube sound is better than that. Tube sound is now about refinement, a sound that never fatigues or is edgy.

Couldn’t agree more. Very well said. If folks don’t listen past the tonal balance of a tube amp (which I suspect is usually the first thing most people notice about any system/room), they’re basically missing out on one of the strongest aspects they offer.

@knotscott tonality is the first thing most people hear. But like you and avanti1960 said there is so much more. I notice the decay in the hall or the lingering tone from the instrument itself. cant list it all as there is so much going on. When people ask what I am looking for it would sound like every other audio enthusiast. Yet we all yearn for something just a little bit different. I tell people I'll know when I hear it!

at least to my ears, lately it seems more and more tube power amps tend to sound similar to Ss amps.

That's because you're listening to tube amps that have feedback and probably PP outputs combined with single-ended input circuits. That tends to make them sound 'solid state'. Transistors often sound that way (harsh, bright) due to insufficient feedback, same as what you see in tube amps.

The warm, rolled off tube sound as it were. 

Most tube amps aren't rolled off in the highs unless there is a malfunction. Some are in the bass, especially SETs, since bandwidth is hard to get with SET output transformers.

always I want a tube amp to sound unlike an SS amp… mostly. as the result of distortion? of course not. ultrra euphonic? nope. not that either.

People don't like to hear this, but the primary differences we hear in all amplifiers is due to their distortion signature. People call that the 'sonic signature' but to be clear it really is about distortion. This is simply because the ear converts all forms of distortion into tonality.


The catch here is that the ear pays a lot of attention to tonality that arises due to distortion. There's a tipping point; the ear may actually favor tonality due to distortion over actual frequency response. This is why tube amps with no feedback and arguably more frequency response error due to a higher output impedance might still sound more neutral if distortion is otherwise properly controlled in the circuit.


A peculiarity of the ear that IMO/IME is not well understood appears to be that the presence of the 2nd and 3rd harmonics (in sufficient amounts with respect to the higher orders) can help the ear winnow out soundstage  and detail (there are limits to this; distortion of any type also obscures detail). I'd really like to find out why this is so. As best I can make out since you can't get rid of distortion, what becomes important is to have a benign distortion signature; if that happens it seems that the actual THD the amp has is far less important. That said there does seem to be limits in this regard; if the amp has 10% THD its likely to be less detailed than an amp with only 1% at full power. So the take away appears to be that if your THD is very low, it still has to have the right signature in order for the amp to sound musical.