SO ~ what gives an AMP it's character or tone ???

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  • ChrisMusicChrisMusic Frets: 1133
    edited August 2014
    Thank you for talking me out of it, I was in dangerous territory for a moment there...

    The cat thanks you too btw.  She always thought it was a bad idea.

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  • monquixotemonquixote Frets: 17485
    tFB Trader
    The main bit of confusion seems to be that because Fenders tend to have 6L6 or 6V6 and Marshalls have EL34s that all amps with those valves sound a certain way when that isn't really true.
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  • karltonekarltone Frets: 44
    In terms of power amp valves there is less difference than you may think between say a 6L6 and an EL34, its more to do with impedance, the EL34's will crunch up sooner than the 6L6. Changing preamp valves makes usually subtle differences which to some makes all the difference to others possibly not.

    Guitar > Amp circuit > Speaker (and style of cab) are the trinity that really shape your sound, the rest is just fairy dust to sprinkle on top to your taste.
    www.karltone.co.uk    Dealer in Valves and bits and bobs   www.facebook.com/karltonevalves
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  • ChrisMusicChrisMusic Frets: 1133
    Actually @monquixote, I blame you entirely for this part of the "tone quest" I am on right now.  The learning part of it is quite fun though, I always had a thirst for that sort of thing.

    I was quite happy with my DT25, for the time being at least, and it sounds good and is pretty flexible.  But, when I came over and tried that rather drab looking PRS SC you were selling, the whole setup you let me try just sounded magical.  There was nothing missing, but there was a delicacy and sparkle that I was somehow missing.  I was captivated.

    I have been kicking myself ever since for not buying the guitar straight away, a bit of a "plain Jane that goes like a train" if you will pardon my phraseology.  It felt absolutely superb, and the P90s were just purr-fect.  A bit like you, for me it didn't have the visual presence or aesthetics, just drab dark brown satin mahogany, so I guess that swayed me, bad move on my part. The one that got away, or one of them anyway.  I would love to have it now though.  The neck and fretboard just felt sublime, and it sounded like that too.

    I keep meaning to ask you what your amp was, model and spec as this discussion is about that sort of thing.

    Missed opportunity, still life's like that sometimes.


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  • Thanks for the points about cab and speaker @guitarfishbay.

    As an aside, what was the quality of the clean channel on the Mesa Roadster you recently sold.
    Does it do Black/Silverface Fender well, and if so any particular comparison come to mind ?
    Is it right to assume that the clean channel voicing is either derived or copied directly from the LoneStar ?

    I am working on a strategy to test speakers and cabinets out in the hopefully not too distant future.

    Any advice on a strategy to ease the financial and time burden of narrowing things down would be appreciated.
    The initial "benchmark" starting point if the result of collective wisdom on here, so collective strategising seems an appropriate path to take too.

    I only play closed back cabs so I can't draw any direct comparisons with Fenders. However the clean modes on it are fantastic, smooth, deep and with a nice sparkle if you dial it in for a brighter sound. Personally I think it has the nicest cleans on any high gain amp I've tried. The main negative with it IMO is how picky it is about cabs. I honestly think the matching Rectifier V30 cabs make all the difference for it. I've not tried them, but I'd imagine the clean channels would sound great through the Lonestar cabs too.
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  • ICBMICBM Frets: 71956
    karltone said:
    In terms of power amp valves there is less difference than you may think between say a 6L6 and an EL34, its more to do with impedance, the EL34's will crunch up sooner than the 6L6. Changing preamp valves makes usually subtle differences which to some makes all the difference to others possibly not.

    Guitar > Amp circuit > Speaker (and style of cab) are the trinity that really shape your sound, the rest is just fairy dust to sprinkle on top to your taste.
    Exactly.

    It was interesting when I compared my two Mesa Trem-o-verbs, each set up with "Fender" and "Marshall" valves sets - one with 6L6s, 5V4 rectifiers, 7025s and a 12AT7 phase inverter (all GE), and the other with EL34s, GZ34s, and ECC83s throughout (all Mullard) and compared them.

    In the "middle" settings - with all the controls roughly centred, give or take a bit - there was almost no difference between them. Certainly one didn't magically sound like a Fender and one like a Marshall, they sounded like very slightly different Trem-o-verbs. It was only when I deliberately pushed them in a more Fendery or Marshally direction by using the controls at or near the extreme ends of their ranges that it was more obvious which one was which. In other words the valve types help to reinforce the sound of the circuit and not the other way round.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ChrisMusicChrisMusic Frets: 1133

    ChrisMusic said:   Thanks for the points about cab and speaker @guitarfishbay.
    As an aside, what was the quality of the clean channel on the Mesa Roadster you recently sold.
    Does it do Black/Silverface Fender well, and if so any particular comparison come to mind ?
    Is it right to assume that the clean channel voicing is either derived or copied directly from the LoneStar ?
    guitarfishbay said:   I only play closed back cabs so I can't draw any direct comparisons with Fenders. However the clean modes on it are fantastic, smooth, deep and with a nice sparkle if you dial it in for a brighter sound. Personally I think it has the nicest cleans on any high gain amp I've tried. The main negative with it IMO is how picky it is about cabs. I honestly think the matching Rectifier V30 cabs make all the difference for it. I've not tried them, but I'd imagine the clean channels would sound great through the Lonestar cabs too.

    Thanks for that @guitarfishbay.  I remember you saying that you tried the Zilla 2x12 cab but the removable rear panel flexes too much under pressure.  That should be fairly easy to cure with a bit of batten, foam strip, and some T nuts, which is the way they should have done it IMHO, or at least to have braced the back panels to stop flexure when used as close backed.

    The Rectifier cabs use a Mesa spec V30 as far as I am aware, so I guess that voicing is a big part of how they sound.
    What was your experience with other speakers with that amp ?

    How would you say that the Roadster compared to a clean Fender if you were to put them in the same room ?

    The Road King does look very tempting with all the progressive linkage, EL34 & 6L6 switchable power sections etc, but I could buy a small country for the money they cost, so it's not really an option for now.

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  • ICBMICBM Frets: 71956
    The Road King does look very tempting with all the progressive linkage, EL34 & 6L6 switchable power sections etc, but I could buy a small country for the money they cost, so it's not really an option for now.
    There are small countries that weigh less, too.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ChrisMusicChrisMusic Frets: 1133
    There was a rather large number in the weight part of the specs on that amp, do the sell them by the kilo then ?

    Yes ICBM, that "progressive linkage" stuff came about from my Fender clean amp discussion and your recommendation to look at the Blue Angel.  Thanks for the recommendation.  I haven't deserted that thread, but this one seems to have taken over for now.  I found a clip on YouTube of an amp for sale some time ago with worse pot issues than Jimi Hendrix.  But while it was working right it sounded sublime.  Now that has both 6v6 and EL84 power sections.  Complexity, and flexibility, and great engineering, that is right up my street.

    Surely both that and the Road King suggest that the power tubes do have a noticeable influence on character ?

    I am interested to see if I am interpreting this right, as I appreciate the points both you and @karltone raised about the differences in power valves being subtle, but that seems somewhat at odds with those Mesa amps.  Or again, am I missing something ?

    "In other words the valve types help to reinforce the sound of the circuit and not the other way round."  That is a very nicely crafted statement ICBM.

    Hopefully when the dust settles and my brain stops spinning all the advice and wisdom in this discussion will crystallise into an innate understanding.   

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  • ICBMICBM Frets: 71956
    The Blue Angel actually perfectly illustrates how *little* the power valves affect the sound - there is a noticeable difference, but it's not huge. In any case, it's at least as much due to the impedance mismatch between the three options, which itself has quite a significant effect on the tone with most amps.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ChrisMusicChrisMusic Frets: 1133

    ICBM said:   The Blue Angel actually perfectly illustrates how *little* the power valves affect the sound - there is a noticeable difference, but it's not huge. In any case, it's at least as much due to the impedance mismatch between the three options, which itself has quite a significant effect on the tone with most amps.
    So I have to ask for an explanation.  What is the effect of impedance mismatch, how would you describe its character and extremes ?  This is another area of unknown valve territory for me, so it will be good to breakdown some more boundaries.

    For me even the YT demos of these amps show a marked difference in tonal character, to my ear, and that's with dodgy recording, YT compression algorithms, and through my iMac speakers.  Mesa must think there is enough mileage in it to engineer a top line product with this as a feature, or is it mostly marketing hype ?

    I don't know if you missed my earlier two posts asking about cathode biasing, valve manufacture, and the benefits of starting Tolex wars ?
    and the one after.

    No worries if you did, but I would appreciate a brief explanation of cathode biasing if you could put it in a paragraph or two.  It would help to round out that part of my understanding.  Thanks.

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  • Another amp that sort of agrees with ICBM is the 6534+.  It's a Peavey amp, and is basically a 6505+ but with an EL34 power section instead of 6l6.  It sounds... Pretty much the same actually, to be honest, whether it's all preamp gain or clean/crunch.  

    It does sound a bit different, I noticed it mostly in the bass, but you'd be hard pressed to say which was 'better'.  
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  • ICBMICBM Frets: 71956
    So I have to ask for an explanation.  What is the effect of impedance mismatch, how would you describe its character and extremes ?  This is another area of unknown valve territory for me, so it will be good to breakdown some more boundaries.

    For me even the YT demos of these amps show a marked difference in tonal character, to my ear, and that's with dodgy recording, YT compression algorithms, and through my iMac speakers.  Mesa must think there is enough mileage in it to engineer a top line product with this as a feature, or is it mostly marketing hype ?
    It isn't marketing hype, but it has as much to do with the impedance as the valve types. 

    The 6V6 setting has effectively about double the impedance of the EL84 setting, and the Simul setting is lower than both (because both sections are in parallel). This means that the 6V6 setting is actually running into about half the proper impedance - ie a low mismatch. This makes the sound more compressed, softer and 'flubby'. Mesa actually recommend that if the amp is going to be permanently run on the 6V6 setting, that you restore the correct match by plugging the 8-ohm speaker into the 4-ohm jack.

    I would guess the EL84 setting is about the correct match, although I don't know the exact ratio. The sound is tighter, brighter and more 'even', which is what a good match normally sounds like.

    The Simul setting is then a slight high mismatch, which means that you don't get quite the combined power from both sets of valves (only 38W, vs 33W for the EL84s and 15W for the 6V6s) but you get a typical extended frequency response, less compression, and a cleaner more 'hi-fi' tone.

    It's very useful for changing the character of the amp depending on whether you want to push it, or use it as a clean platform for pedals etc. (At least, that's how I used mine.) But you will notice that all three settings sound like a Blue Angel, just different. It doesn't suddenly sound like a Deluxe Reverb or an AC30 just by changing the power valve setting.

    I don't know if you missed my earlier two posts asking about cathode biasing, valve manufacture, and the benefits of starting Tolex wars ?

    No worries if you did, but I would appreciate a brief explanation of cathode biasing if you could put it in a paragraph or two.  It would help to round out that part of my understanding.  Thanks.
    Cathode bias means that the valve bias is generated by the current through the valve passing through a resistor in the cathode connection. This means that the bias is dependent on the current, and becomes self-regulating - it's also called 'self bias'. The hotter the valve runs, the more voltage is produced, which in turn runs the valve cooler. That also means that when the valves are overdriven and start to conduct much more current, the bias rises a lot which limits the output power at just above that point, so you get a very compressed sound.

    Different valves do definitely sound different - although some amps are much more sensitive to it than others - but it's one of those things which is less important than the major factors, until you start to compare different valves in the same amp. You're very unlikely to be able to take two amps in isolation and tell what valves are in them just by listening, although you could make a good guess as to the type of circuit, type of cab design and possibly the type of speakers.

    And yes, tolex does make a small difference - at least if you compare a tolexed cabinet to the same cab with none, it's surprisingly noticeable how much more vibrant they sound without it. I think it's pretty unlikely that different types of tolex sound noticeably different though! And it's also way further down than the cab design or materials.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Dave_McDave_Mc Frets: 2324
    Probably the fact that someone famous used it at some point.
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  • ChrisMusicChrisMusic Frets: 1133
    That's brilliant ICBM, as always.  I really appreciate the descriptive sound results of the technical issues, thats very helpful.
    I am actually getting quite excited learning all this stuff about valves.  Cheers.  :)

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  • monquixotemonquixote Frets: 17485
    tFB Trader
    Actually @monquixote, I blame you entirely for this part of the "tone quest" I am on right now.  The learning part of it is quite fun though, I always had a thirst for that sort of thing.

    I was quite happy with my DT25, for the time being at least, and it sounds good and is pretty flexible.  But, when I came over and tried that rather drab looking PRS SC you were selling, the whole setup you let me try just sounded magical.  There was nothing missing, but there was a delicacy and sparkle that I was somehow missing.  I was captivated.

    I have been kicking myself ever since for not buying the guitar straight away, a bit of a "plain Jane that goes like a train" if you will pardon my phraseology.  It felt absolutely superb, and the P90s were just purr-fect.  A bit like you, for me it didn't have the visual presence or aesthetics, just drab dark brown satin mahogany, so I guess that swayed me, bad move on my part. The one that got away, or one of them anyway.  I would love to have it now though.  The neck and fretboard just felt sublime, and it sounded like that too.

    I keep meaning to ask you what your amp was, model and spec as this discussion is about that sort of thing.

    Missed opportunity, still life's like that sometimes.

    I feel it's incumbent upon me to say that tone is in the fingers :)

    That PRS was quite special. Though the DGT that replaced it is a far more versatile guitar (and much prettier) the Satin had the best neck of any guitar I've ever played. Infact the bloke I sold it to sent me an email asking if I was insane for selling it :)

    The amplifier is an H&K Puretone. It's an interesting case study in what amplifiers should sound like being bull. 
    For example it's EL34 so it should sound like a Marshall, but it doesn't, it's class A (or not ICBM will say) so it should sound like an AC30 but it doesn't, it has a V30 so the cleans should sound "harsh", but they don't.
    What I think is true about it is that it's a very simple circuit made out of very chunky well built components in an extremely solid birch cabinet.
     
    They are a bit of a bargain SH considering they are £2K new and Guitarist list them in their list of best boutique amps along side Two Rock etc.

    I should also add that some of the lovely room filing nature of the sound was probably the Flint and the SP comp which add a bit of subtle magic.
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  • CatthanCatthan Frets: 355
    edited August 2014
    Thanks for starting this thread @ChrisMusic, I m learning a lot.
    One for @iCBM, Mesa Simul class A side, is it "true" class A or hot AB?
    so enjoying my MkV, don't know how much Simul has to do with it..

    one thing about power valves from a practical standpoint;
    My first good amp time being a Suhr Badger 30 with power scaling, I was able to somewhat experience the difference between power valves as power scaling lowers the clipping threshold of the power-stage so you can blend more of its sonic character in the tone at low volumes. Between several brands of el34s and a pair of kt66s I could hear the difference and if I lowered the power it was very noticeable.

    which brings me to the point: unless you push the amp really hard the contribution of the power-stage is less noticeable. 
    Now practically, how many of us push their amps that hard? Specially those with >50?
    I never even had to push my 30 watters (badger & LSS) higher than 12:00 as I'd overload the stage sound and mess everyone up. There is a voice I think in every type of power tube but as said the circuit dictates how much of that voice comes out. Unless you crank an old amp like a plexi which relies heavily on the power stage, I don't think you will get much more than what the circuit dictates from the power valves. Not without some sort of attenuation which imposes other compromises.
    and then there's the argument of whether what we think is power-valve clipping is actually the PI clipping.. But I'll leave that to the experts.
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  • ecc83ecc83 Frets: 1589

    Putting some numbers on a cathode biased stage might shed some light on why it is hardly ever used for output stages past about 30watts.

    If we take an EL34 and wish to bias it to a modest 50mA* the grid voltage would be around 30V and so the bias resistor, for one valve, 600Ohms. Guitar amp op stages always share a single resistor so, twice the current, half the resistance=300 Ohms. It is simple to show the resistor would dissipate 3watts and so a 5W, better 10W component is needed. It will still get quite hot so need to be kept away from other components, especially electrolytic caps.

    A pair of 34s so biased with say a 300V HT would probably put out 20-30watts. To get more power we would have to increase the HT to 400, 450 even 500**volts.THAT would mean anode current would rise and the grid voltage needed to bias it back even higher and that means Rk is higher in value and thus dissipates even more power. We lose more and more output voltage swing to the cathode. Connecting the cathodes to earth, neg HT, and generating a negative bias voltage elsewhere improves efficiency greatly.

    *I nave NOT looked up the curves so I don't know if a 50mA bias is feasible but surely the numbers will serve for "demonstration"?

    **500V actually hits the 25W anode dissipation limit for the EL34 and 50mA Ia.

    On the subject of different output valve "sounds"? It is often overlooked that different types have very different drive requirements or sensitivities (gm). For instance the venerable 6V6 and the EL84 are very different in this respect so in an "EL84" amp, V6s are going to make the PI work much harder for the same power output.


    Dave.

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  • ICBMICBM Frets: 71956
    edited August 2014
    There are some cathode-biased guitar amps which use separate resistors - the Orange Rocker 30, several Matamps and the Cornell 18/20 are a few I know of - but it's fairly rare. It also makes the amp "sound more fixed-bias" compared to a shared resistor, I'm not quite sure why!

    The Mesa Simul-Class is unusual in that the 'Class A' section is fixed-bias, but I'm not sure if it's true Class A or not - it is low-powered enough that it's possible. It also runs in triode mode which sounds quite different from tetrode/pentode, which may be more important than the class!

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ecc83ecc83 Frets: 1589
    ICBM said:
    There are some cathode-biased guitar amps which use separate resistors - the Orange Rocker 30, several Matamps and the Cornell 18/20 are a few I know of - but it's fairly rare. It also makes the amp "sound more fixed-bias" compared to a shared resistor, I'm not quite sure why!

    The Mesa Simul-Class is unusual in that the 'Class A' section is fixed-bias, but I'm not sure if it's true Class A or not - it is low-powered enough that it's possible. It also runs in triode mode which sounds quite different from tetrode/pentode, which may be more important than the class!

    Yes! Should have said "almost all" use a common cathode resistor. I did ask once a B's why two are so rarely used but they could not tell me either! I doubt that the saving of one R and cap would be it!

    The HT-20 biasing is unusual. About 12 volts of it comes from cathode bias* but there is also a negative supply with setting and balance control. Not sure why they went that way? One advantage is of course that the V loss in the cathode circuit is only about a third of full CB.

    One operational advantage is that you can swap the 34s pretty much with impunity and the bias will come up about right. Best of course to get it set and balanced soon as...

    *At first glance it looks as tho' the 20 has separate cathode Rs but in fact it is two 7 watters in parallel.


    Dave.

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