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Old 7th April 2011, 04:06 PM   #1
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Default question for you geniuses about distortion

I understand the great sound of early rock amplifiers came from the way their power amps distorted. I understand how and why this would happen and how that would affect the overall amp response to playing. But how important, power amp distortion is for these modern ultra high gain amps (i.e. mesa dual rec and peavey 5150)? How much power amp contributes to their tone? I know that at low volumes their already sound great, so this led me to assume that most of their sound (at least what i can get from low volumes) comes from their preamp distortion. Unless i am missing something and they also have power amp distortion at low volumes....

Thanks for the help
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Old 7th April 2011, 04:19 PM   #2
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I dunno what think geniuses, but I think may be you like clean sound as well as distorted?
Because when tube amps distort they distort musically. But when they are clean, they are extremely clean. If you want the cleanest sound, tubes are the way to go.
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Old 7th April 2011, 04:50 PM   #3
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Hello. Thanks the reply, but i am not sure i understood it. I am interested in the relationship between preamp and power amp distortion for modern high gain amps...How much of power amp distortion contributes to their overall distorted tone...
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Old 7th April 2011, 05:03 PM   #4
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Is there a particular amp you are reffering to as they all sound a little (some more than) different from one another and most (not all) of the differences in sound depend on the type of speaker system or systems that are used.

Just as one tube may sound different than another tube even though they are the same type (or number) and even the same maker in some cases.

The same is possible in soild state systems aswell although less likely. jer
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Old 7th April 2011, 05:06 PM   #5
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As i mentioned on my first post, i am talking about amps on the likes of mesa dual rectifier and peavey 5150...I am not talking about specifics of each induvidual amp, but the groeling distortion people use for heavy metal these days....
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Old 7th April 2011, 06:14 PM   #6
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Quote:
Originally Posted by hpupo View Post
As i mentioned on my first post, i am talking about amps on the likes of mesa dual rectifier and peavey 5150...I am not talking about specifics of each induvidual amp, but the groeling distortion people use for heavy metal these days....
These days a lot of metal guys prefer to use pedals to create distortion rather than get if from overdriving their amps.

I play in a band that is not metal, but we recently played in a show that was all metal- except for us. Now I've seen a lot of shows at this particular venue, and I knew that the mic *everything*, but I was surprised to see how small some of the guitar amps were- as little as 25 watts! Without the PA, none of the metal bands would have been all that loud.
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Old 7th April 2011, 06:23 PM   #7
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I really appreciate everyone's input on this, but i still dont have a answer from a technical perspective, which is really what i am looking for.
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Old 7th April 2011, 06:37 PM   #8
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Quote:
Originally Posted by atmasphere View Post
These days a lot of metal guys prefer to use pedals to create distortion rather than get if from overdriving their amps.

I play in a band that is not metal, but we recently played in a show that was all metal- except for us. Now I've seen a lot of shows at this particular venue, and I knew that the mic *everything*, but I was surprised to see how small some of the guitar amps were- as little as 25 watts! Without the PA, none of the metal bands would have been all that loud.
I think the quick answer might be that amps with a "master volume" and "gain" controls depend on the preamp for the sound.

The "modern" way to get power-tube distortion. Build a smaller amp. Then you can over drive it without creating sports-stadium level volumes.

If you are after a classic rock or blues kind of sound you can get it with preamp distortion and a rather clean power amp stage. This way your master volume control can be used. It takes more then two 12ax7 gain stages to have the full effect.

I just recently built a tube based "pedal" (the box is way to large and is AC powered to be called a pedal but is is used the same way) using two 12AX7 stages. It has a tube overdrive sound, believe me if you drive a 12AX7 with a 90 volt peak to peak signal it will clip, big time and make a sound not that much unlike a power tube driven to clipping but I think the preamp sounds different because a 12AX7 class-A triode can't cause the power supply inside an amp supply to sag like a pair of push-pull EL34 can.
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Old 7th April 2011, 06:46 PM   #9
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Hi hpupo,

I am not sure, I can answer your question with regards to a technical perspective.
My Marshall 6100/30th anniversary runs with 4 EL34 in the power amp.
The distortion of the lead channel sounds pretty much like modern/new metall.
This is pretty independent of the volume - you have to get above a certain volume to let the 4x12" speaker "breath" but this is far from running the power amp into saturation. At the same volume setting, even the bass notes in the clean channel are still glass clear and clean (for guitar player ears not Hifi ears).
This would imply that the distortion HAS to be generated in the preamp stages.

The control experiment: Running the same amp on only 2 EL34 in triode mode (possible in this model) can give you nice overdrive sounds in the "crunch" channel. With this setting and at higher volume, the clean channel is not clean any more - obviously the power amp is now starting to clip.
Interestingly, this sounds entirely different. Much more like the old rock n' roll sound - definitely not what you would associate immediately with metal.
In this case, the use of good pedals (distortion or just boosters, like Rangemaster) really makes a difference and a lot of sense.

I realize, this was not a technical answer, but I hope you can read between the lines that this strongly argues for preamp-only distortion in "modern" high gain amps, if one can generalize this at all.

Cheers,
Martin
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Old 7th April 2011, 07:05 PM   #10
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A lot of the early guitar amps were built "wrong" so that there was a distortion component in the sound. It probably started out as the manufacturer trying to save money and later evolved to deliberate choices as players began exploiting the performance envelope.

You could introduce it at any or all stages, although since you want some consistency in control settings it probably was limited.

Single-ended stages produce harmonically rich distortion. Tube amps tend to have large overload margins, with consistently rising distortion components, so you can run the amp in an area of operation that generates predictable distortion levels.

You can't use as much Negative Feedback in a tube amp (due to the output transformer and it's effect on phase) ... low or no NFB will create higher distortion that is none the less consistent with the amps distortion signature.

Cheap unregulated power supplies would tend to sink and result in higher distortion with sustained signals at the same volume setting. So, you can introduce distortion just by adjusting playing style with the classic amps, or choose pickups or guitars that can exploit that characteristic. Some amps use tube rectification to deliberately sink the supply to get a similar effect where solid state rectification would tend to be more robust and therefore cleaner.

Output transformers can be deliberately chosen (on newer amps) or were simply installed to save money (original classic amps) that were inadequate for low distortion output. Thus higher distortion at rated output.

Circuit design and parts selection in the preamp stage can influence the distortion characteristics of the amplifier. Also, as mentioned earlier, large overload margins can be exploited to overdrive a following stage.
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Last edited by Johnny2Bad; 7th April 2011 at 07:14 PM.
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