Physics !

Paul_C

Why valve amps are best. . .

https://phys.org/news/2017-02-physics-musicians-valve-amps.html

olafgarten

That explains why you can get good cleans and high gain from SS, but not the crunch. 

Jeremiah

Don't single ended and push-pull valve power stages behave differently in terms of the balance of odd/even harmonics?

ICBM

Jeremiah said:

Don't single ended and push-pull valve power stages behave differently in terms of the balance of odd/even harmonics?

Yes. Which is why the article is bollocks, as usual… trying to reduce something extremely complex to overly simple 'rules', and not properly comparing either like with like or taking account of some of the more important factors.

Using a single example of a Bugera hybrid amp with a (partly) valve preamp and a solid-state power stage to try to understand the difference between a valve amp and a solid-state amp, when the power stage has at least as much effect, is not going to produce very much useful information.

Push-pull power stages - including valve ones - inherently cancel even-order harmonics (at least those generated in the power stage itself).

Cirrus

I think the even harmonics = good, odd harmonics = bad thing is over simplistic to the point of being worthless, really. When you get into the physics of harmonics, consonance, dissonance etc, it seems very much that we're clutching at straws to explain why certain intervals work and others don't.

For example, there is an interval - somewhere around the "Blue note" 3rd, that in terms of its overtone series is more consonant that either a minor or major 3rd. And a 4th is more consonant than a 3rd, so why do modern western ears hear a 4th as an unresolved chord? The same thing goes for an interval that's between a 6th and a minor 7th. A thousand years ago a major 3rd or a 7th chord would have sounded as dissonant to their ears as the "petrushka chord" (Cmaj and F#maj triads) sounds to our ears.

In truth, I think we learn the language of music as babies/children and the reason we prefer valve amps is that the sound of a typical overdriven 12ax7 or power stage with particular circuit architectures is just a sound that we're used to. It's more "musical" because it's essentially defined the musical environment we live in over half a century.

ICBM

Cirrus said:

I think the even harmonics = good, odd harmonics = bad thing is over simplistic to the point of being worthless, really.

In truth, I think we learn the language of music as babies/children and the reason we prefer valve amps is that the sound of a typical overdriven 12ax7 or power stage with particular circuit architectures is just a sound that we're used to. It's more "musical" because it's essentially defined the musical environment we live in over half a century.

That, and the fact that valve amps have some accidental characteristics that make them respond dynamically and in terms of EQ in what sounds like a very natural and instinctively controllable way, especially when played loud in a band context - but it's *not* to do with harmonics.

I think the 'harmonic' thing has come about because an overdriven direct-coupled solid-state power stage will often produce a fairly good approximation of a square wave, which contains a lot of odd-order harmonics and thus 'odd harmonics sound bad' because square waves sound unnatural - there are no naturally-occuring sounds which contain them. Whereas an output transformer as you find in a valve amp struggles to pass a square wave - which in theory is effectively composed of sections of DC separated by vertical transients, neither of which can pass through a transformer - and actually modifies it into something closer to a sawtooth wave… which contains even-order harmonics, and sawtooth waves do occur naturally.

So really the 'valves produce even harmonics and transistors produce odd harmonics' idea is untrue, it's just that the circuits they're used in tend to do that to some extent - but more importantly in the power stage than the preamp.

Voxman

There's an east dis-proof of that article - its called the Bluetone Pro 30M, which is a pure SS amp that sounds and behaves like a valve-amp, one of which is owned by Pete Townshend who I think knows a thing or too about tone!:

 http://www.guitarplayer.com/miscellaneous/1139/blue-tone-pro-30m/18830

Dave_Mc

ICBM said:

Jeremiah said:

Don't single ended and push-pull valve power stages behave differently in terms of the balance of odd/even harmonics?

Yes. Which is why the article is bollocks, as usual… trying to reduce something extremely complex to overly simple 'rules', and not properly comparing either like with like or taking account of some of the more important factors.

Using a single example of a Bugera hybrid amp with a (partly) valve preamp and a solid-state power stage to try to understand the difference between a valve amp and a solid-state amp, when the power stage has at least as much effect, is not going to produce very much useful information.

Push-pull power stages - including valve ones - inherently cancel even-order harmonics (at least those generated in the power stage itself).

Yeah I thought it sounded like guff. I just waited until someone more knowledgeable was willing to stick their neck out and call it.

It suggests you pick harder when playing lead... if anything I pick more quietly.

Plus lead playing is often single notes, while rhythm playing is often chords... which gives the amp a bigger signal i.e. more distortion. (I think.)

And those aren't the only two ways to increase gain, either- a boost pedal? Turning up your guitar volume control? Etc.

I mean even without delving into the science, it's garbage even to someone who plays guitar, really.

ChrisMusic

Voxman said:

There's an east dis-proof of that article - its called the Bluetone Pro 30M, which is a pure SS amp that sounds and behaves like a valve-amp, one of which is owned by Pete Townshend who I think knows a thing or too about tone!:

 http://www.guitarplayer.com/miscellaneous/1139/blue-tone-pro-30m/18830

Not so sure about the dis-proof, from the Blue Tone article:

"But here’s the real magic: Cooper also developed a really hip circuit that mimics the non-linearity of the Marshall’s phase splitter and output tubes, as well as the output transformer’s saturation characteristics and the 4x12 cabinet’s resonance and dynamic loading effects on the output stage. Residing on a 4" epoxy-encapsulated PC board, this ambitious solid-state, analog modeling circuit is the most essential component of Blue Tone’s proprietary Virtual Valve Technology."

"... and a pair of blue LEDs monitor each half of the Virtual Valve Technology’s push/pull output stage simulator. These Blue LEDs begin to illuminate as the amp makes the transition into overdrive. The red Clip LED on the far right indicates when the output is being driven beyond its ability to track the signal’s full dynamic range."

Sounds like a potentially inspired design, I would love to hear / play one.


Here is a bit more about the methodology and measurements in the OP's rather more simplistic article.

http://iopscience.iop.org/article/10.1088/1361-6552/aa57b7

Although I do agree with both you and ICBM, that it is flawed, especially by the "Bugera Assumption"   :-B

thermionic

It has a couple of good bits in it, but on the whole it's a very flawed, terrible paper. The editor should be ashamed to have allowed it for publication!

Dave_Mc

^ We need more rock guitarists as Journal Editors...

thermionic

Even better, rock guitarists with PhDs in physics

ICBM

Brian May has one in astrophysics, is that close enough?

hywelg

One of the main reasons Dumble ODS's have a trimmer on the anodes of the PI is to balance the powerstage It's been shown clearly that a well balanced output stage will minimise odd order harmonics to the benefit of even order harmonics. 

ICBM

hywelg said:

One of the main reasons Dumble ODS's have a trimmer on the anodes of the PI is to balance the powerstage It's been shown clearly that a well balanced output stage will minimise odd order harmonics to the benefit of even order harmonics. 

Actually the exact opposite. If the output stage is perfectly balanced it will cancel the even-order harmonics completely and sum the odd-order harmonics, that is a characteristic of push-pull stages.

thermionic

ICBM said:

Brian May has one in astrophysics, is that close enough?

Er, I was thinking about myself!

I have met two people who have PhDs in the physics of acoustic guitars, including The Rock Doctor, if you ever get the chance to see him, he's a great speaker. 

Cirrus

There's a nifty little effect plugin called SDRR by a company caled Klanghelm, it's a distortion plugin that offers a few different modes - you get a mixing desk, fuzz, digital and valve distortion models.

The valve model has a control that lets you chose the blend between even and odd harmonics, and it's pretty interesting how while they both have different characters in terms of what they do to the sound, they both sound like distortion and more often than not I prefer the odd harmonics because the even ones seem to get in the way of other sounds more.

Just a little thought I had.

Dave_Mc

ICBM said:

Brian May has one in astrophysics, is that close enough?

I was thinking about nigel tufnel