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power amp distortion
power amp distortion
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Old 19th May 2011, 01:56 AM   #1
hpupo is offline hpupo
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Default power amp distortion

What type of distortion characterizes a guitar power amp? I mean, power amp distortion is most due to the non linearity of the tubes, or does guitar power amps actually clip? How much clipping is acceptable? Does that matter for single ended and push pull?

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Old 19th May 2011, 11:01 AM   #2
trobbins is offline trobbins  Australia
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The type that your non-linear ears and non-linear brain 'enjoy the most' when listening at suitable sound levels from your non-linear speakers. When all the non-linearities align - and your grinning from ear to ear - than thats the solution.

Change any one of those non-linear elements and you come up with a new solution.

It isn't trivial - most guitar amp manufacturers aim for their own blend of distortion - so most people start with a common manufacturer's amp that they like, and tweak/clone from there.
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Old 19th May 2011, 12:29 PM   #3
MrCurwen is offline MrCurwen  Finland
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If you like the old style screaming dirty guitar sound, then yes, that usually does involve the output stage clipping.

However, if you don't rehearse in a stadium, you're gonna need an attenuator.

Another route would be to build subwatt power stages, which are a bit more friendly on the ears and neighbours. Also much, much cheaper!
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Old 19th May 2011, 01:41 PM   #4
TheGimp is offline TheGimp  United States
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Single ended will have more 2nd Harmonic content while it is canceled to a greater extent by a push pull output.

You could use a PPIMV (Post PI Master Volume control) to control power out, but it is limited and you can't dial down a 30W amp to 1W or less.

What/where are you intending to play? Bedroom? Garage band? ???
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Old 19th May 2011, 02:06 PM   #5
hpupo is offline hpupo
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Thanks everyone for the replies. After a sleepless night thinking about, i was able to understand why it clips...
Would you guys know if these modern heavy metal amps (best example is peavey 5150) rely also on power amp distortion? My reasoning is that in order for them to clip the power amp, they would have to be at extremely high sound levels, which i know is not the case since i tested a few of them at low levels...but maybe im missing something...
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Old 19th May 2011, 03:52 PM   #6
pedroskova is offline pedroskova
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you don't have to clip the output to create distortion. Your output could instead accurately reproduce distortion from your driver stage. Pick a wimpy input tube that is incapable of driving your output tube, and voila... low power distortion.

Having said that, i know nothing about guitar amp design.
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Old 19th May 2011, 03:59 PM   #7
quikie22 is offline quikie22  Malaysia
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clipping distortion in guitar amps need not necessarily occur at the output (with a loud screech), it can be done at the pre-stage, at the distortion stage.. at the first drive stage... and then the distorted signal fed to the output stage through a volume control.... which will reproduce the distorted signal at whatever level you set on the volume control...
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Old 19th May 2011, 07:22 PM   #8
MrCurwen is offline MrCurwen  Finland
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Power amp distortion usually makes the sound really compressed and dirty, that kind of sound hasn't been fashionable for decades, really. Modern distortion from tube amps is primarily from several, often as much as 5, gain stages in the preamp, each distorting the sound a little bit.

You can get close to the old kind of Hendrixy-Creamy sound with just different preamp things, leaving the power stage clean (with post PI master volume). I'm quite happy with such an arrangement myself.
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Old 20th May 2011, 05:05 AM   #9
andrew_k is offline andrew_k  Australia
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Originally Posted by hpupo View Post
if these modern heavy metal amps (best example is peavey 5150) rely also on power amp distortion?
Absolutely not. Truly heavy distortion amps ('teh brutalz') depend on a clean power amp stage to have immediacy and clarity in the attack with each note. The "chug chug" sound falls to pieces in an overdriven power amp. As stated previously, these amps get their distortion from multiple preamp gain stages, often biased hot/cold/hot/cold such as the classic Soldano.
Designing preamps for Guitar and Bass is an excellent book if you want to learn more on the subject.

Personally I LOVE power amp distortion in a guitar amp. If a 6V6 PP amp running wide open is too loud for your space, get a less efficient speaker.
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