What exactly is "tube warmth"?

[mistermikev]

"if you gotta ask... you can't afford it" hehe jk.
I'm torn... I love digital gear... and perhaps it's placebo - I can't rule that out - but when I turn on my tube preamps or send my digital gear into a tube poweramp I still feel like there is something special there.

 

[rickdog]

Tubes Versus Transistors -- Is There an Audible Difference? (archive.org, 1.2 MB PDF download)
Russel O. Hamm, Sear Sound Studio
Journal of the Audio Engineering Society, May 1973, Vol. 21, No. 4

This is worth setting aside an hour or more, pouring your favorite beverage to enhance contemplation, and reading carefully. It's not too technical, but does contain some enlightening graphs.

 

[agedhorse]

Thanks a lot for your replies. They are pretty informative... stay tuned... I might make a different thread about neo cabs and traditional "weight-a-ton" speakers

I think it's quite interesting to have a glimpse of what companies think when designing new products, whether it is because they are trying to get themselves into a pretty well-established trend, or when they are trying to put some new concepts or designs in the market (peavey's trans-tube technology comes to mind)

When designing new products, it’s critical IMO to understand what the perceptions of the player are, and especially how they might be changing. Nothing in music is static, it’s always changing.

 

[Patrice B]

Tubes Versus Transistors -- Is There an Audible Difference? (archive.org, 1.2 MB PDF download)
Russel O. Hamm, Sear Sound Studio
Journal of the Audio Engineering Society, May 1973, Vol. 21, No. 4

This is worth setting aside an hour or more, pouring your favorite beverage to enhance contemplation, and reading carefully. It's not too technical, but does contain some enlightening graphs.

Your link appears to be broken, malformed…

https://ia802207.us.archive.org/28/...AnAudibleDifference/TubeVsTransistor_text.pdf

 

[rickdog]

Your link appears to be broken, malformed…

https://ia802207.us.archive.org/28/...AnAudibleDifference/TubeVsTransistor_text.pdf

Thanks... I just copied & pasted from my browser's download history, I didn't think to test it, something about how the browser recorded it, I guess....

 

[Patrice B]

Thanks... I just copied & pasted from my browser's download history, I didn't think to test it, something about how the browser recorded it, I guess....

Correct me if my resume of the study is wrong: grossly, in ‘73, this study showed that the overload of silicon vs tubes difference was that with tubes, it was mainly the second, third, fourth and fifth harmonics appearing. However, they weren’t at the same amplitude, the stronger being the second (octave). It appears to our ears as « ticker ».

In the case of transistors and op amps, it was mainly the third and the following uneven harmonics but rising at approximately the same level, human ear interpreting it as harsh and unpleasant.

Contrary to the beliefs, tubes weren’t necessarily more slower when transitioning to higher THD as it is often mentioned as an explanation.

 

[Patrice B]

 

[agedhorse]

With transistors or tubes on similar open loop or low ac local feedback circuits, it’s not mostly 2nd harmonics.

OpAmps are an entirely different topology which requires high global feedback, which changes the harmonics when clipped.

 

[Patrice B]

With transistors or tubes on similar open loop or low ac local feedback circuits, it’s not mostly 2nd harmonics.

OpAmps are an entirely different topology which requires high global feedback, which changes the harmonics when clipped.

Thanks, I stand corrected… Sorry for the confusion. Quite interesting read none the least.

The study looks to be focused on preamp distortion but no mention of feedback loops???

 

[agedhorse]

View attachment 4814197

Note that for a mic pre, approx 30-50dB of gain is required. Transistor designs often use over 100dB of open loop AC gain with moderate global feedback, OpAmp designs can use over 150-200dB of open loop gain with much higher feedback to reduce the gain to 30-50dB closed loop.

N the article, they neglect this important bit of detail that’s a little like the elephant in the room.

 

[agedhorse]

Thanks, I stand corrected… Sorry for the confusion. Quite interesting read none the least.

The study looks to be focused on preamp distortion but no mention of feedback loops???

Correct, different topologies use different combinations of local versus global feedback.

 

[Lostgallifreyan]

Tubes Versus Transistors -- Is There an Audible Difference? (archive.org, 1.2 MB PDF download)
Russel O. Hamm, Sear Sound Studio
Journal of the Audio Engineering Society, May 1973, Vol. 21, No. 4

This is worth setting aside an hour or more, pouring your favorite beverage to enhance contemplation, and reading carefully. It's not too technical, but does contain some enlightening graphs.

Thanks for that. I read the first few pages, and it got very interesting for me in something not directly valve-related, but I wanted to mention it in case it's not just interesting to me.

In an earlier post I said to @agedhorse that I'd added nonlinear methods to a synthesiser I was writing in software. It's not aimed at emulating valve sound, or tape saturation, but I discovered some things that looked and sounded interesting, they modified waves in ways similar to the diagrams in fig 5 and fig 7 in that PDF.

One of my methods was a log domain scalar, but a trickier variant (which needed some special variable offset correction) is an asymmetric log domain scalar that does similar things. The log domain scalar is a bit like an instantaneous compression when biased one side of its neutral setting, and expansion on the other. It sounds a bit like tape saturation, or the flare in a brass instrument, depending on what gets modified by it..

The asymmetrical one is even weirder. As with the descriptions earlier in that PDF, where someone says a tube bass sound seemed to have an octave lower component in the sound, my asymmetrical log domain scalar does this too. There are lots of ways to add such harmonics in a phase mod synth, any DX7 can do it, but having subtle nonlinear distortions, variable in realtime, is not something I'd seen before as a deliberate design in a synth. I didn't aim for it either, it was just idea that sounded good, and different depending on what sound it was applied to. One of the most overwhelming characteristics of these methods is that unlike PWM (which I also added) the scalar methods will almost always produce a very nice musical alteration to the sound, a kind of edge that 'agrees' with whatever is modified by it. That suggests that it's these sorts of nonlinearities that may be making tubes/valves sound better to many people.

 

[ThisBass]

Correct me if my resume of the study is wrong: grossly, in ‘73, this study showed that the overload of silicon vs tubes difference was that with tubes, it was mainly the second, third, fourth and fifth harmonics appearing. However, they weren’t at the same amplitude, the stronger being the second (octave). It appears to our ears as « ticker ».

Not neccessarily. Too much amount of a second respectively those even order harmonics does not sound good anymore.
A very similar thing does happen with very mild/smooth saturation, cause once the saturation was very smooth/mild then the outcome of total sound was quite muddy and spongy.

Furthermore, if there was two gain stages that are acting in series connection in the signal path of an preamp, odds may be emphasized (the odds produced by gain stage #1 are added by odds produced by gain stage #2), while the even order harmonics may nearly completely cancel out each other (gain stage #2 does cancel out the evens that are produced by gain stage #1).

In total the sound of odds harmonics THD may be perceived as a tuby sound with "warmth", some self trained experts may argue this is done by all the even order harmonics produced by tubes, and there are at least two tube gain stages producing them but, in total there may be nearly no even order harmonics anymore, even with tubes.

In the case of transistors and op amps, it was mainly the third and the following uneven harmonics but rising at approximately the same level, human ear interpreting it as harsh and unpleasant.

With tubes there may be already odds (and evens) present for small signal considerations but, it strongly depends on the schematic design of the tube stage.
A tube gain stage without a cathode R bypassing C may show pretty good linearity.
Those tube stages have been prooven to be pretty much "robust" versus tube rolling.
And quite often folks THEN try to "tweak" the sound of those tube stages with tubes that are NOT designed for those tube schematics in question.

 

[Snert]

If no to second point, maybe.

No to both.
My response was a local slang expression meaning, yeah, I heard you, but nah, you're wrong.

 

[ThisBass]

View attachment 4814197

This article does neglict a basic problem with those AB-considerations.

For both amplifiers the signal was gained to 3% THD.
It is not stated how much of THD was produced by saturation.
The signal of the tube preamp may already carry ~1.5% THD just before the signal begins to saturate.
This means the signal of the preamp may carry already 1.5% THD within its clean range without saturation.

The SS preamp may carry only 0.3% THD within its clean range.

1.5% THD added to the tube preamp signal that was caused by saturation.
2.7% THD added to the SS preamp signal that was caused by saturation.

I think its comprensible that the tube preamp may sound cleaner vers. the SS preamp, althogh the THD was just the same.

 

[ThisBass]

Semiconductor clipping enhances the odd harmonics, valves enhance the even ones. Combine that with their more gentle onset due to saturation, and you get the bulk of any explanation I can think of.

There is not much of components needed,
Op-Amp, three diodes, some resistors, job done.
The schematic will produce plenty of 2nd and even order harmonics at overload range.
Alernatively combinations of Z-diode and or Ge/Si diodes do also the job to produce even order harmonic stuff.


edit:
with an proper arrangement of diodes its even possible to provide a tuby sounding flavour (even and odds) even for an OP-amp stage at clean output range.
I don't reacall how I did it in the past, I'd have to look in my documents about the way I designed it.
But, even if I would recall, I wouldn't tell anyway how the schematic looks alike.

 

[seamonkey]

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.

 

[chadhargis]

Warmth (doesn't have to be from a tube) is the coloration of tone that makes it less "precise". It gvie

Tubes Versus Transistors -- Is There an Audible Difference? (archive.org, 1.2 MB PDF download)
Russel O. Hamm, Sear Sound Studio
Journal of the Audio Engineering Society, May 1973, Vol. 21, No. 4

This is worth setting aside an hour or more, pouring your favorite beverage to enhance contemplation, and reading carefully. It's not too technical, but does contain some enlightening graphs.

Readers Digest Version:

The transistor characteristics which our subjects noted were the buzzing or white-noise sound and the lack of 'punch." The buzz is of course directly related to the edge produced by overloading on transients. The guess that this is white noise is due to the fact that many of the edge harmonics like the seventh and ninth are not musically related to the fundamental. The ear hears these dissonant tones as a kind of noise accompanying every attack. The lack of punch is due to the strong third har- monic which is inaudibly "blanketing" the sound. This is correctable by using a large enough pad to prevent all peaks from reaching the amplifier's saturated region. But from a practical standpoint, there is no way of determining this on most consoles. Adding auxiliary peak indicators on the input preamplifiers could alleviate both these problems, and the sound would be very close to that of the operational amplifier in its linear region.

Vacuum-tube amplifiers differ from transistor and operational amplifiers because they can be operated in the overload region without adding objectionable distortion. The combination of the slow rising edge and the open harmonic structure of the overload characteristics form an almost ideal sound-recording compressor. Within the 15-20-dB "safe" overload range, the electrical output of the tube amplifier increases by only 2-4 dB, acting like a limiter. However, since the edge is increasing within this range, the subjective loudness remains uncompressed to the ear. This effect causes tube-amplified signals to have a high apparent level which is not indicated on a volume indicator (VU meter). Tubes sound louder and have a better signal-to-noise ratio because of this extra subjective head room that transistor amplifiers do not have. Tubes get punch from their naturally brassy overload characteristics. Since the loud signals can be recorded at higher levels, the softer signals are also louder, so they are not lost in tape hiss and they effectively give the tube sound greater clarity. The feeling of more bass re- sponse is directly related to the strong second and third harmonic components which reinforce the "natural" bass with "synthetic" bass [5]. In the context of a limited dynamic range system like the phonograph, recordings made with vacuum-tube preamplifiers will have more apparent level and a greater signal to system noise ratio than recordings made with transistors or operational amplifiers.



Cliff's Notes Version:

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

 

[Lostgallifreyan]

There is not much of components needed,
Op-Amp, three diodes, some resistors, job done.
The schematic will produce plenty of 2nd and even order harmonics at overload range.
Alernatively combinations of Z-diode and or Ge/Si diodes do also the job to produce even order harmonic stuff.


edit:
with an proper arrangement of diodes its even possible to provide a tuby sounding flavour (even and odds) even for an OP-amp stage at clean output range.
I don't reacall how I did it in the past, I'd have to look in my documents about the way I designed it.
But, even if I would recall, I wouldn't tell anyway how the schematic looks alike.

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..

 

[ThisBass]

Honestly, at least to me the Readers Digest content sounds like intentionally mental enfeeblement