Power Amp Saturation versus Pre Amp Overdrive

Discussion in 'Amps and Cabs' started by stevel, May 1, 2008.

  1. stevel

    stevel Member

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    I'm sure this has been gone over before, but the searches I tried were to no avail.

    I have a little Marshall Combo (900 series "high gain").

    I read these things about hitting the Power Amp Tubes hard, etc. etc.

    How do I do this?

    There's a gain knob (which I know is preamp gain) and a master knob (which I know is power amp gain) - note - it's two channel but for the sake of simplicity, I'll just discuss one.

    And I've got my guitar which has its own "gain".

    So, if I "hit the preamp hard" does that mean the level of signal going into the amp at the input jack - i.e. from the guitar?

    Or, does turning up the gain knob "increase the input to" the preamp section (i.e. like boosting before going into the amp). Or, does it "increase the OUTPUT to" the power amp section?

    Likewise, does turning up the Master volume increase signal to the power amp section (i.e. hit the power amp tubes harder)?

    What I'm basically getting at is, with Gain 1, and Master 10, do I get more power tube saturation than with Gain 10 and Master 1?

    (I know I know - I should just go outside and try it, but I'm one of those people who need to constantly reassure themselves and who likes to understand what's happening)

    This amp will run on 1/2 power as well. Will running it on half power not hit the power amp section as hard as running it on full power?

    Finally, there's an effects loop, which is preamp out, power amp in. I've noticed I can put an EQ in there, or a clean boost, and get a really nice amount of saturation, but they also affect the tone (runnning the EQ with all faders maxed has a different EQ shape than with them at 0 and just cranking the gain on the EQ for example).

    So looking at an effects pedal - let's say a clean boost - if I put it at the input I'm hitting the preamp section harder, right? And if I put it at the effects return, I'm hitting the power amp section harder, right?

    So I guess what I'm looking for is to hit the power amp section as hard as possible with just the amp's settings, and then pushing a little further with something - most likely in the FX loop.

    TIA for any wisdom on this issue.

    Steve
     
  2. fizbin

    fizbin Member

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    1. Turn the master all the way up or defeat it (use an attenuator if necessary to get appropriate actual volume)
    2. Turn the channel volume/gain up
    3. Not tried this but I've heard of guys running boosters in the effects loop

    Very likely, but they are sort of working together so attenuating either will effectively result in less power tube saturation.

    Gain 1, Master 10 is likely going to sound very clean in spite of whatever power tube saturation you're getting.

    Why aren't you just trying this for yourself and listening for what you like? It really sounds like an attenuator might be a good investment for you.
     
  3. hamfist

    hamfist Member

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    I'm going to add that many people actually don't like power tube break-up, or saturation. It is not the holy grail of all guitar tone freaks.
    Amps like the Jcm900 are designed around pre-amp distortion. However, this does not mean that a certain level of power amp gain will not add a pleasing "fullness" that would not not be there otherwise.
    Basically, try it all ways, at all levels, and see what sounds best for you. Because, in the end, that is all that matters !!

    BTW, I do agree that an attenuater would be a very useful tool to enable you to play about with power amp levels, and still be able to keep your hearing intact !
     
  4. bosstone

    bosstone Member

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    What??? Many people don't like power tube break-up??? I guess I might as well get a guitar preamp and put it through my stereo.
     
  5. popsongsmith

    popsongsmith Senior Member

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    good one. I too hate that "Angus" tone. so thin and buzzy...
     
  6. Dave

    Dave Member

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    Well, I guess I must like "thin and buzzy" because Angus has great tone IMO.
     
  7. popsongsmith

    popsongsmith Senior Member

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    sorry, I guess the sarcasm didn't come through...or did it?
     
  8. Warren Mendonsa

    Warren Mendonsa Member

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    I guess most guitar players like a combination of the two. I like my basic tone to be shaped by preamp distortion, and then 'fattened' with a touch of power amp distortion. With an amp like the Suhr Badger, you can hear what just power amp distortion sounds like while running a relatively cleaner preamp - I didn't like it at all.

    On all the vintage non-master amps, you're hearing preamp and phase inverter distortion combined with power stage (and perhaps output transformer and speaker) distortion, so it's kinda pointless to say that it's exclusively poweramp distortion you're hearing on those glorious tones. Think of it as just in (important) ingredient in your tonal recipe.

    I used to play JCM800 and JMP master volume amps for ages, and I used to be frustrated trying to get a full sounding tone at whisper volumes late at night. I somewhat compensated by using the Bass and Mids on 10 and treble on 0. When I got the Suhr Badger, it was stupidly simple to dial in exactly how much power amp distortion I wanted.

    If you ask me what it adds to your tone, I'd say it fattens up your lows (bloom) and smoothens out the harsh fizz. Hope that helped : )
     
  9. stevel

    stevel Member

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    Well, I got it :).

    Steve
     
  10. Mr. Brady

    Mr. Brady Member

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    Hey Warren,

    Do you have any clips of you with the Suhr badger? I still listen to your album at least once a weak. Love the guitar playing and tone. It's inspiring.
     
  11. guitarslinger21

    guitarslinger21 Member

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    a power amp doesn't need to break up to influence the tone.

    IMHO, power tube breakup is overrated.

    It's a concept chased by 70's fanboys and n00bs.


    play what sound good. (in my case, 6550's and the circuit designed around them influence the tone BIG time, but don't add any distortion to my preamps.
     
  12. hamfist

    hamfist Member

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    Well said GS. I agree completely.
    Personally, I do not like noticeable power tube break up. I like the fullness the power tubes can add when pushed a little bit, but once they start noticeably breaking up, it all gets rather mushy and saggy for my tastes.
    Many people may think that they are getting power tube break up with many NMV amps. But actually when you fit a PPIMV to one of these amps, and experiment a bit, one finds that the vast majority of the breakup is from the pre-amp and PI tubes. For example, a Plexi on 7 or 8 really isn't getting much power tube break up in my experience.


    Well, maybe some people just need to get out a little more and mix with a few different people, and realise that the whole world isn't full of people just like them. ;)
     
  13. Julia343

    Julia343 Member

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    Well, after several months, I said f--- it. I cranked my Deville up to 11 clean and attenuated the signal to where the output was about 95 db at about 6 ft. It was a great Fender tone. I found out what Keeley was talking about the Java Boost needing an amp that's at least starting to overdrive. That gave a much better sound. There was a fullness to the clean tone without being mushy (like the drive channel on this amp gives).

    Pre-amp overdrive alone sounds thin and fizzy. Cranked, my high gain pedals didn't need so much gain. Everything sounded clearer and less harsh. The entire rig sounded better. Very Fenderish classic rock. Yes it's loud, but my cable is long enough to get out into the hall so as not to damage hearing. I own my home and the neighbors have been trained.

    Yes I'm still getting my Marshall, but I'm keeping this amp. It can't do Marshall. Nor can Marshall do Fender, no matter what they say.
     
  14. JimH

    JimH Member

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    Hello Steve - I'll try and answer your questions as best I can...

    Very complex issue this and there are varying opinions on it - your logic and questions are reasonable -surely you can't 'hit a power amp hard' without a big signal coming from the preamp. - with what are you hitting it??? So logically that means hi pre amp gain? - well I suppose so - however what people usually mean by this power amp stuff is this:

    Presumably you've tried your amp with pregain up and master vol down? - to get distorted tone at low enough levels so as not to annoy the neighbours.. right? - sounds a bit thin, buzzy, wasp in a jam jar? - yet when you're with a band you turn the master up and hey presto sounds great? - Well people have put this down to the power tubes not working hard enough -others put it down to a poorly designed master volume circuit. Others forget all that and use an attenuator - I've got power scaling installed in my amp so I can control the level at three stages in the circuit - some guys even put it down to the speaker distorting more. In all probability it's a bit of everything, however the sound people generally want isn't the one with a big Marshall amp with gain on 7, master on 1.

    - isn't a boost in the loop just adding gain to the preamp signal...? - yes but does it sound better to you? go for it.
     
  15. Warren Mendonsa

    Warren Mendonsa Member

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    Not yet, though I'm working on it. Glad you're still enjoying the album : )

    Someone has very kindly uploaded all my older clips here if you'd like to listen: http://www.divshare.com/download/2895281-940
     
  16. wildschwein

    wildschwein Member

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    It depends on what type of power tubes you're talking about. 6L6s don't sound so great when breaking up - lots of compression and sag when you overcook 'em. EL-34s and EL-84s still compress but are a little more buttery.

    Personally, I don't think valve preamp distortion sounds are much more special than a solid state front end distortion tone. I guess that's why there are a lot of folk out there who still love their Music Man amps. Also from the JCM 800 on, with the exception of the very first models, Marshall started using solid state electronics to generate the preamp distortion in their amps.

    I don't think the preamps valves really deliver the tube voodoo. I'd rather a solid state front end and a partially breaking up tube power section than a tube front end and a clean high wattage solid state power amp. Most of the tube mojo happens in the power section and some distortion is the key to it all - along with a number of other factors. That's why most hybrid amps sound like crud. Guess after 19 years of playing I'm still a "n00b."

    I'm not 100% sure what a "70s fanboy" is but the 1970s was the period when more amp manufacturers developed amps with more preamp gain stages and master volumes etc. Mesa made their mark here, Fender started putting distortion knobs on their amps and the 1st Marshall master volume models were developed around this time. This development in the industry came about as a way to mimic power amp distortion that many guitarists had grown fond of, at least since the 50s. It was just a way of providing something similar to guitar amp consumers at a lower volume. Preamp distortion is in fact just a model of power amp break up developed and marketed firstly in the 70s - although there may have been experimental amps that had similar features made in the 60s.

    Generally speaking, a 70s sound could be characterised/emulated more by/with preamp distortion tones, especially in relation to 60s guitar recordings. Although I'm probably ignoring solid state distortion devices/pedals which wound up on a lot of recordings and influenced the front end sound quite a lot in both decades.
     
  17. michael patrick

    michael patrick Supporting Member

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    I think the classic Marshall crunch is a combination of preamp and power section distortion.
     
  18. Uniphasian

    Uniphasian Member

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    One of the original questions asked about the location of the gain pots in the chain - does the Gain pot control the level going into the gain stage or coming out of that stage?
     
  19. Whiskeyrebel

    Whiskeyrebel Member

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    Correct me if I'm wrong, but I think it controls the percentage of the signal coming out of the stage that is fed to the next stage. So a MV amp would have this adjustment in at leats two places - the gain being located between two different stages of the preamp, and the master being located between the end of the preamp and the power amp.
     
  20. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    The way I'd put it is, if guitar players like the distortion sound when their amp is turned up loud, then chances are, they are hearing the combination of the two and that combination is actually what they like. It's not often practical (or possible) to play with only power amp distortion...and how "good" it is will vary from amp to amp.
     

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