What exactly is "tube warmth"?

[ThisBass]

That early post of mine was a starting point for me in this thread, not one I will cling to. I've made some more later that might be more useful.

One possible feature of opamps that might be interesting is slow slew rate. It's not exactly a filter anyone would calculate with formulas, but it can produce some weirdly 'squelchy' artifacting that re similar to things I've heard from some circuits when driven hard. It's not a sound I like, but some people might..

If I remember correctly about the filter, LPF -6dB/octave

edit:
for the audible range of bandwidth 20Hz..20kHz the LPF effects do not matter, by no means.

 

[Lostgallifreyan]

If I remember correctly about the filter, LPF -6dB/octave

I think I've heard that before, certainly 3dB and variable 12dB, but the slew thing I mentioned was qualitatively different. I don't know the maths for it in any way I could describe here, but an example can be found in the Sound Forge program. It's probably crude, has just 5 settings, and is a kind of LPF in a literal sense, but the way it sounds with higher settings is like no ordinary filter I ever heard. What it does remind me of is some of the early sounds in heavy rock, that almost burbling sound that comes from amps and cabs driven that hard, but those are complex effects there, so this may be purely subjective, and brains fill in the gaps as best they can, so any resemblance I found may be spurious..

 

[ThisBass]

I think I've heard that before, certainly 3dB and variable 12dB, but the slew thing I mentioned was qualitatively different.

Try to imagine that besides audio applications op-amps are also used for many extremely high precisively instrumentation measurement applications.
If slew rate "accuracy" was an issue, such as you might think, all of these op-amps where not suited anymore for the most part of industrial and military usage.

 

[agedhorse]

Cliff's Notes Version:

Tubes sound better when you crank 'em up because their distortion sounds good.

Not necessarily, there are tube circuits that sound terrible when overdriven, but these share similar topology elements with transistor (and op-amp) circuits of the same type (ie. high open loop gain, high global feedback)

One possible feature of opamps that might be interesting is slow slew rate. It's not exactly a filter anyone would calculate with formulas, but it can produce some weirdly 'squelchy' artifacting that re similar to things I've heard from some circuits when driven hard. It's not a sound I like, but some people might..

Generally, when slew-rate limiting occurs, it's pretty awful sounding. The curved parts of the higher frequency sine waves become straighter and the transition from positive to negative slope becomes triangular like because the change in signal occurs faster than the op amp (and global feedback correction) can track it. This means that the amplification and especially the negative feedback is always lagging the signal at higher frequencies.

 

[ThisBass]

Warmth is add some mild distortion and turn down the treble.

For distortion, it's a mix of even and odd harmonics that sounds the most familiar and thus probably better. It's very easy with any DAW to display what the harmonic structure of a sound. Take a look, it's a mixture.

For preamp tubes (for the most part of MI preamps) there is almost always both kinds of saturation valid.
Once a preamp tube (at a gain stage) does saturate, one 1/2 of the signal is soft clipped at its output, while the other 1/2 of the signal is hard clipped at its input stage, and 1:1 amplified to its output.

Thus we do see almost always "both worlds" of clipping with preamp tubes, hard clipping and soft clipping simultaneously.

 

[chadds]

3,5,7th harmonics sound more pleasant. A good musician with good gear can make it happen. The good musician is going to pick the combo or amp and cab by ear. This good musician could have started playing weeks ago. That person is using their ears.

So the pre plus the amp plus the cab make their sound. Myth? You can't get this with SS. Well you can but the "butter" is in some well intentioned tube design. Personally if your pre is big and pronounced and powerful then the amp is just your amplification. Your personal PA. Just for this conversation make sure your fatness is farther up your signal chain.

 

[Doug4321]

Hmm, never had a tube amp all these years. But the “tube amp emulation sound” from pedals, like Tech21 etc. sounds like some tone color, like scooped, notched or comb filtering. Maybe some compression and distortion too. Distortion/overdrive definitely if you turn that up.

 

[aleclee]

At least among guitar players, it's an abstract term used to rationalize the cost, weight, and inconsistent tone of their rigs. It's crazy how many things (temperature, humidity, line voltage, tube wear) can impact a guitar amp's tone, particularly a high gain amp.

 

[TyBo]

At least among guitar players, it's an abstract term used to rationalize the cost, weight, and inconsistent tone of their rigs. It's crazy how many things (temperature, humidity, line voltage, tube wear) can impact a guitar amp's tone, particularly a high gain amp.

I wouldn't think of it as abstract, really ... kind of the opposite, an experienced feel when playing the amp. Kinda like some sports cars - when it's running right it's really something (and they'll usually run right for a good stretch of time). But then ... definitely more of a pain than most solid state amps.

 

[Lostgallifreyan]

Try to imagine that besides audio applications op-amps are also used for many extremely high precisively instrumentation measurement applications.
If slew rate "accuracy" was an issue, such as you might think, all of these op-amps where not suited anymore for the most part of industrial and military usage.

I agree, it's hard to pick a slow slew rate amp now, even the instrumentation grade amps that don't put speed as their top requirement. Anyway, as @agedhorse says, it sounds bad when it does happen so we can rule it out as a contributor to desirable tone.