Preamp vs Power Tube Distortion

[Guitar Toad]

Does Preamp distortion come from using a dist/od pedal infront of the amp or are modern amps designed to generate more preamp distortion than power tube distortion?

How much is amp design vs pedal usage?

I'm guessing the older amps like the Bassman and JTM 45 are the best examples of power tube distortion. And that's why they have a reputation for being loud amps. They gotta be loud for the the sweet power tube OD point to be reached. Am I getting it right?

 

[Pink Unicorn Horsey]

Re: Preamp vs Power Tube Distortion

Modern amps, or "master volume" amps, have multiple gain stages. You get pre-amp distortion from running the pre-amp tubes, and you get power amp distortion from running the power tubes. An overdrive pedal pushes the signal from guitar to amp a bit more, making the tubes work harder.

Many folks say, and I agree, that you need to get those power tubes nice 'n' hot to get a really full gain tone. If you're cranking the gain on your Mesa but leaving the master volume low, you're only working the pre-amp tubes hard, which leaves the gain tone more buzzy and not as full.

The ultimate is to get the pre- and power tubes running hot, plus getting some breakup by getting the speakers to move some air.

- Keith

P.S. There's a lot more to it than what I've stated here. I suspect this will be a long thread!

 

[The Golden Boy]

Re: Preamp vs Power Tube Distortion

The only time you'd be using a pedal as the "preamp" is if you ran that into the "In" of your effects loop.

The preamp takes the line signal and amplifies it to a signal level that the power section can use. Preamp distortion (or overdrive) is just pushing the preamp to its overdriving point- then that distorted signal is amplified. At tamer volumes the power amp isn't overdriving, it's just pushing the distorted preamp signal.

Dig?

 

[drew_half_empty]

Re: Preamp vs Power Tube Distortion

with power tube distortion, as i understand it, a lot of it has to do with how much negative feedback is in the circuit

so yes a jtm45 is a good example

from my expirience, preamp distortion is that kinda cello-y sounding distortion, and poweramp distortion is that real greasy kinda sounding distortion

then again jeff seal used to say what most people describe as poweramp distortion is actually phase inverter distortion

 

[Guitar Toad]

Re: Preamp vs Power Tube Distortion

I hear lots of guys say "slam the preamp with a pedal".

And I read in a Laney amp manual how they state they are using a new amp design to correct the unhealthy use of preamp distortion.

I read in another site where the Fender Twin Reverb was designed with a bleed to drain gain off the preamp tubes to prevent distorted signal from reaching the power tubes.

Then there's the speaker breakup that factors into the equation as KG suggests.

 

[Lake Placid Blues]

Re: Preamp vs Power Tube Distortion

When you push a NMV amp with a OD pedal out front, the signal going into the first pre-amp tube in louder, this in turn means that the signal coming from the pre-amp to the power amp will be a lot louder and this will result in pushing the power tubes harder as well. I suspect that the pre-amp tubes get pushed to distortion a bit as well, so the result is both pre-amp tube and power tube distortion mixxed.

Power tube distortion is a better sounding distortion to my ears, being warmer and sweeter. ......... Some may not even consider it to be much "distortion" in this age of high gain super saturation.

 

[Guitar Toad]

Re: Preamp vs Power Tube Distortion

A bit of nomenclature clarification for me...Preamp tubes distort and power tubes overdrive?

 

[some_dude]

Re: Preamp vs Power Tube Distortion

I hear lots of guys say "slam the preamp with a pedal".

Back when preamps had a limited amout of gain it became popular to "slam the front end" with a pedal. Basically, you're adding an extra gain stage to boost the signal level enough so that you get more distortion out of the first preamp tube.

Modern high gain amps usually use extra tubes for those extra gain stages, so the first gain stage boosts the level up to get more distortion out of the second gain stage.

Same process, slightly different method.

 

[Lake Placid Blues]

Re: Preamp vs Power Tube Distortion

Well there's a noticable difference in the distortion texture with diffrent power tubes, regardless of the pre-amp or phase inverter tube. A Marshall with 6550's is a lot cleaner than EL34's. A KT66 is yet another flavor. If you change to a 12AT7 PI tube, the amp will get more clean head room because it drives the power tubes less, so I think it's still a matter of the power tubes overdriving.

I think power tubes are harder to push into a hard "clip". As they run out of headroom, they start to compress the wave rather than flatten the signal, so that might be a good way to look at it.

Another factor effecting the headroom of the power tubes is the power supply. I think that tube rectification goes better with a power tube overdrive amp.

 

[Pink Unicorn Horsey]

Re: Preamp vs Power Tube Distortion

A bit of nomenclature clarification for me...Preamp tubes distort and power tubes overdrive?

This site should clear up some of your questions.

- Keith

 

[Guitar Toad]

Re: Preamp vs Power Tube Distortion

Preamp amplifies the signal it receives. The preamp increases that amplitude of the signal. If the signal coming in is already big relative to the tubes head space (i.e. the limit of the max signal that the tube can handle) , the preamps tubes amplification will square off the wave and then send that square wave to the power tubes for additional amplification. That will send the power tubes to or beyond their limits.

But if the preamp amplifies the signal but has sufficient headroom, then the power tubes will amplify what they receive and retain the proper wave form. From what I understand the sweet power tube OD is when the power tube signal approaches the tubes head room, and the signal wave gets "clipped" and not abruptly squared off.

This is why stuff like amp biasing and tube matching are important.

 

[Guitar Toad]

Re: Preamp vs Power Tube Distortion

Are the following appropriate examples?
The Angus Yound AC/DC tone is Power Tube distortion/overdrive.
Lamb of God is loaded with pre-amp driven distortion but likely is has pre-power tube distortion going on.

ZZ Top Gimme All You Loving is both.

 

[Kommerzbassist]

Re: Preamp vs Power Tube Distortion

and the signal wave gets "clipped" and not abruptly squared off.

Clipping and squaring off is the same... basically, the more the signal is clipped, the more it looks like a square wave.

 

[Pink Unicorn Horsey]

Re: Preamp vs Power Tube Distortion

Are the following appropriate examples?
The Angus Yound AC/DC tone is Power Tube distortion/overdrive.
Lamb of God is loaded with pre-amp driven distortion but likely is has pre-power tube distortion going on.

ZZ Top Gimme All You Loving is both.

I think those are good examples, although I don't know a lot about Billy Gibbons' setup on that particular tune. A hybrid example of the "both" scenario is Eddie Van Halen's early "brown sound" setup, which involved the use of a Marshall's pre-amp stage (with tubes) and an H&H solid-state amplifier to amplify the signal.

I think I've got that right.

- Keith

 

[Axl H]

Re: Preamp vs Power Tube Distortion

I prefer a mix.

You get the smoothness and tightness of the preamp, combined with the raw and warm sound of power amp OD.

I run my setup so that a BD-2 pushes the front end, then some Preamp drive, into the power amp, cranked so loud the speakers are distorting.

Loud? Yes. Gain? Hell yes

 

[some_dude]

Re: Preamp vs Power Tube Distortion

Are the following appropriate examples?
The Angus Yound AC/DC tone is Power Tube distortion/overdrive.
Lamb of God is loaded with pre-amp driven distortion but likely is has pre-power tube distortion going on.

ZZ Top Gimme All You Loving is both.

All three of them have both pre and power tube distortion going on but in different proportions.

I try not to worry about what is preamp and what is power amp distortion....I only worry about whether it sounds good.

 

[Guitar Toad]

Re: Preamp vs Power Tube Distortion

All three of them have both pre and power tube distortion going on but in different proportions.

I try not to worry about what is preamp and what is power amp distortion....I only worry about whether it sounds good.

Me too. I'm just trying to better develop a better understanding what these terms mean for when this stuff is discussed. I don't have the experience with amps that apparently a lot of guys here have.

 

[Axl H]

Re: Preamp vs Power Tube Distortion

One thing I have learnt.

One thing is having LOADS of gain, another thing is controlling it.

I usually run the volume on my guitar at 4-5,and let the amps the do the work.

 

[Pink Unicorn Horsey]

Re: Preamp vs Power Tube Distortion

It's surprising when you discover how little gain a lot of heavy rock guitarists use. Aerosmith and Kiss are great examples of this. Their music may sound heavy, but they're not always cranking the gain.

 

[Axl H]

Re: Preamp vs Power Tube Distortion

I dont use that much, because I have the volume low on the guitar.

But I have it if I need it.

I also pound my guitar hard, except when I solo.