Explain power tube and pre amp tube Distortion?

[jammath]

:NUTS If you could explain in laymans terms the difference between the two!

Here are a few examples of some songs that i'm curious about!

Led Zep- How the west was won?
aerosmith-live:sweet emotion?
Rush-Early live stuff? thanks!!

[boobtoob]

I'll give it a shot, matey.


Power tubes are bigger and put out alot of watts...enough to drive big speakers.
Preamp tubes are smaller and put out less than 1 watt...not enough to drive big speakers.


When you turn up the vol on the power tubes enough, you get distortion that is loud.

When you turn up the vol on the preamp tubes enough, you get distortion, but it is not so loud. So the output from it is fed into another amplifier to make it louder.

[rockon1]

Yeah but if you turn up the volume enough on a non master volume amp you very well may get pre amp tube distortion anyways. One of the reasons MV's were added was to get that pre amp distortion at a lower volume.I'd say most of all the distortion you hear is pre amp or perhaps PI distortion.

:BEER

[Old Tele man]

...PREAMP tubes operate Class-A1 single-end (SE) and typically generate both ODD- and (predominately) EVEN-order distortion when over-driven.

...POWER tubes operate Class-AB1 push-pull (PP) and also typically generate both ODD- and EVEN-order distortion, but the EVEN-harmonics "cancel" in the push-pull transformer, when over-driven.

...the "big" difference is that PREAMP-induced ODD- and EVEN-order harmonics are simply amplified by the power tubes and not "cancelled" in the OT. The OT only cancels harmonics that are generated within the POWER tubes.

SUMMARY: Preamp distortion contains both ODD and EVEN-order harmonics, while POWER distortion tends to be mostly ODD-order harmonics...and: EVEN-order harmonics sound "thick/rich" while ODD-order harmonics sound "thin/raspy"

[rockon1]

Originally Posted by Old Tele man

...PREAMP tubes operate Class-A1 single-end (SE) and typically generate both ODD- and EVEN-order distortion when over-driven.

...POWER tubes operate Class-AB1 push-pull (PP) and typically generate mostly EVEN-order distortion, which "cancel" in the push-pull transformer, when over-driven.

ask and ye shall recieve!......

[El Caballo]

http://en.wikipedia.org/wiki/Even_and_odd_functions

(scroll down to "Harmonics")

In amplification stages, odd-order harmonics are generated by symmetrical non-linearity, and even-order harmonics are generated by asymmetrical non-linearity. It's easy to generate only even harmonics: use a diode to hard clip half the waveform. I guarantee that it won't sound "thick/rich". You can also generate even harmonics by clipping a Class A transistor stage, and it won't sound "thick/rich" either.

Even in the "tubiest" of tube amps, the amount of even harmonics introduced is small compared to the odd harmonics. Most of what people like about tubes has to do with soft clipping (whether symmetrical or asymmetrical) and dynamic responses over time in different parts of the circuit (most of which get lumped in under the names "sag" and "squish")

Even in something simple like a Bassman/Plexi, there are five amplification stages, of which four can introduce significant non-linearity -- not to mention the effect of the transformer and speakers. So it's not as simple as "preamp vs. power amp."

What is important is the sound you get from pushing your amp and speakers really hard. This produces all sorts of interesting nonlinearities that sound good. "Power amp distortion" is only one of them, and is probably less important than speaker breakup and -- on recordings, which is what we're talking about here -- the proximity effect of the microphone responding to high SPL at close range.

[Blue Strat]

On a slightly more "usable" note, preamp distortion is fuzzy/buzzy like an overdrive or distortion pedal. Power tube distortion is more like compression. Combine the two and REAL tone begins to take place.

[WailinGuy]

Originally Posted by Blue Strat

On a slightly more "usable" note, preamp distortion is fuzzy/buzzy like an overdrive or distortion pedal. Power tube distortion is more like compression. Combine the two and REAL tone begins to take place.

There are no hard and fast rules about this. A lot depends upon the circuits and brand/types of tubes used. For example, a well-designed and implemented tube preamp is capable of generating very warm, smooth, and musical distortion with very little fuzz or buzz.

A common fallacy is that when vintage style, non-master volume amps are turned way up, the distortion you hear is all power tube distortion. (Often there is also the assertion that power tube distortion is always "better" than preamp distortion.) The truth is that a lot (or even most) of the clipping occurs in the preamp and phase inverter circuits. Also, if vintage style speakers are used, they add their own breakup sound to the overall tone.

[Jef Bardsley]

Originally Posted by Old Tele man

...gotta agree with El Caballo, speaker distortion is also a major factor in amplifier "sonics," especially at high volumes!

Yes, yes, speakers are unquestionably an important link in the chain, but if we're going to answer the original question, don't you think we need to confine ourselves to talking about the tubes? Too many of you feel compelled to display your creativity by throwing out red herrings.

Originally Posted by Blue Strat

On a slightly more "usable" note, preamp distortion is fuzzy/buzzy like an overdrive or distortion pedal. Power tube distortion is more like compression. Combine the two and REAL tone begins to take place.

Now, this is a useful generalization. And it's from someone with a bit of experience in these matters (don't be fooled by my new name - I've been around here for years). How about some more similar opinions or disagreements, and less exceptions and special cases?

[El Caballo]

Originally Posted by Glass Snuff

How about some more similar opinions or disagreements, and less exceptions and special cases?

Because, as far as I know, the answer to the question is "you're not hearing much power tube distortion in either case, and what you do hear is not generally distinguishable from preamp distortion."

This is not a helpful answer, because we all know there is a certain sound you get when you crank everything up that you don't get by overloading the preamp. So the question becomes "what's causing that sound?" I don't know enough to give a definitive answer, but the list includes:
1) Clipping/non-linearity in the phase inverter
2) Power supply sag
3) Saturation/other non-linearity in the output transformer
4) The many effects of driving a speaker hard
5) On recordings, the many effects of driving a microphone hard

I'm very interested in hearing from people who know more than I do about the relative importance (or unimportance) of these elements, and about any important elements I've missed.

[Thomas D]

Originally Posted by El Caballo

5) On recordings, the many effects of driving a microphone hard.

IMO this gets overlooked way too often, especially when people are hell bent on doing live what somebody else created in a studio. Which, I'm convinced is often like searching for hen's teeth.

Sure we could limit the discussion to just pre-amp v.s. power amp distortion, but isn't it helpful to understand them in the context of all of the various ways that distortion/compression can occur once the signal is in the amp?

[El Caballo]

Originally Posted by Thomas D

IMO this gets overlooked way too often, especially when people are hell bent on doing live what somebody else created in a studio.

Yes. Probably 80% of all rock guitar is recorded with an off-axis SM57 a few inches from one speaker cone. Proximity effect alone guarantees that this frequency response is nothing near flat. Then there is diaphragm resonance, and probably a lot more things I don't understand yet. A dynamic mic is a speaker in reverse, so a lot of the same things happen.

[jammath]

Thanks! very interesting stuff guys! Technical........but interesting!

[Jef Bardsley]

Another common fallacy is that preamps or stompboxes can equal the glorious sound of a hot pair or quad of push-pull output tubes running full tilt. Kids raised on CDs might believe this, but those of us that can't hear any more know better.

Jam, your first two examples are power tube distortion, as is the work of all the 60's and early 70's tone gods. Lifeson, I'm not so sure about, but if it was live...

A good example of the difference is found in ZZ Top. The early stuff was power tubes (with boxes), but in the eighties, Billy started using more master volume amps (and more studio processing), and the change is obvious. Same player, very different sounds.

Not surprisingly, some of the benchmark powertube tones come from concerts where the amps could really be unleashed. Woodstock - Hendrix, the Grease Band (Joe Cocker), and Leslie West. Live at Leeds - the Who. Rockin' the Filmore - Humble Pie. And one of my favorites, the intro to Sweet Jane on Lou Reed's "Rock and Roll Animal" - Hunter and Wagner.

Unfortunately, power tubes just don't take the beating they used to.

[rockon1]

Originally Posted by Glass Snuff

Another common fallacy is that preamps or stompboxes can equal the glorious sound of a hot pair or quad of push-pull output tubes running full tilt. Kids raised on CDs might believe this, but those of us that can't hear any more know better.

Jam, your first two examples are power tube distortion, as is the work of all the 60's and early 70's tone gods. Lifeson, I'm not so sure about, but if it was live...

A good example of the difference is found in ZZ Top. The early stuff was power tubes (with boxes), but in the eighties, Billy started using more master volume amps (and more studio processing), and the change is obvious. Same player, very different sounds.

Not surprisingly, some of the benchmark powertube tones come from concerts where the amps could really be unleashed. Woodstock - Hendrix, the Grease Band (Joe Cocker), and Leslie West. Live at Leeds - the Who. Rockin' the Filmore - Humble Pie. And one of my favorites, the intro to Sweet Jane on Lou Reed's "Rock and Roll Animal" - Hunter and Wagner.

Unfortunately, power tubes just don't take the beating they used to.

I would venture to say the "power tube" examples you give are actually mixtures of pre amp tube distortion,pi distortion and power tube saturation/distortion. The introduction of MV's allowed for the use of pre amp distortion BEFORE the power tubes were anywhere near saturation and pre amp sections geared toward even more distortion.