Relationship between volume and tone of a valve amp

nikolas7333

We all know that in the world of guitars and amps, there are lots of myths and half truths that are bandied about as gospel. One claim that has interested me for a while is that a valve amp needs to be "opened up" for it to sound good, and/or that power amp distortion is somehow more "organic" sounding than preamp distortion, and I've often wondered how much truth there is to it.

A few years ago, I performed a bit of an experiment, in which I recorded my old Peavey Ultra 60 combo over the full range of its volume knob (and yes, it got bloody loud), and after normalising the signals to allow for the well-known phenomenon that a louder signal is generally perceived as sounding better, it seemed basically that the tone just got more bassy, until it started to sound like shit as the 6L6's distorted. This was done with an SM 57 by the way, which is not the most uncoloured of microphones of course, but still, it seemed to me that I could have achieved the same effect simply by tweaking the EQ.

Obviously that wasn't exactly a scientific way to go about things, but people must have analysed (in a non-subjective way e.g., with a spectral analyser) the signal coming out of an amp at different volumes, so do any of the more techy members know what is it that actually happens? And does it really ever sound "better", once the signals have been normalised, in a way that couldn't be achieved simply by tweaking the EQ?

Nerine

Did you lower the gain as the volume went up?

Also, an output stage literally on 10 or "dimed" (bleurgh) is past the point of good tone usually. The output stage is then so unstable, distorted and compressed that the actual usable tone disappears. This happens more in some amps and less in others, but generally, everything set a bit below 10 or flat out yields better/clearer results.

I also think power amp overdrive is a bit overrated. It always has a weird swirly sound to me, with a bit of fuzz. I can use it and I like it. But I don't think "power amp on ten" is as desirable as everyone makes out. I usually find a bit of shove from the preamp on top of a cooking power section works the best.

But yes, due to all sorts of factors, the amp turned up a bit will always sound better.

nikolas7333

Nerine said:

Did you lower the gain as the volume went up?

No, but I don't remember it really sounding any more distorted as I increased the volume, at least not in a good way, although bear in mind this was quite a few years ago.

In any case, what I'm really interested in is if anyone can really say what actually happens from a semi-scientific perspective, instead of the subjective "it just sounds better" (not knocking your comment by the way). I remember seeing a video in which Pete Thorn did something similar with buffers, really showing that its the top end that suffers with a long cable.

paulmapp8306

Volume is not as relevant for recorded sounds as it is to live sounds.  A big part of the "sounds better louder" isnt that your pushing the PA side harder, but old FM.  The human ear hears different frequencies differently and different volume.  So the louder you go the more bass and treble come through - the quieter the more prominent the mids are. It just means you need to EQ differently for different volumes, but generally amps (particulary older ones) were built to be pushed and EQd for that.

theres also sound pressure to take into account.  The louder the sound, the more air moves, and the more "vibration" relationship between the guitar the and amp take effect.  The guitar is more alive, feeds back/goes into harmonics easier with a loud amp.  Again though this is not really that the amp sounds better, but the whole amp/guitar (and lets face it guitarist) relationship works better at volume.

Once you isolate the guitar from the amp (as you do in a recording - unless your in the same room as the amp), and isolate the human ear from the real amp (again as you do when listening to a recording) the benefits of that volume arnt there.  Its quite possible to get a "wound up " amp and a "quiet" amp, once recorded to sound the same (though the guitarist would feel the difference and the guitar wouldnt react the same during the performance as explained).

So - does a loud amp sound/react better than a quiet one - absolutely.  Does a RECORDED loud amp sound better than a RECORDED quiet one - to the end listener.... Not really.

Maynehead

If I try to play my Dual Rectifier at TV volume levels it sounds so weedy and thin that you'd think there's something wrong with it. I can tweak the hell out of the EQ and it would still sound rubbish. If I fire up my 15W roland cube along side it I can instantly get a better sound.

Now if I start to turn the volume up, the story begins to change. On the rectifier the mids begin to thicken and the bass grows deeper. The treble starts to become less dominating and the fizz disappears. On the roland cube, at the same volumes, the mids start to dominate, the bass and treble start to fade and the tone becomes more boxy and less defined, more muddy.

Ok, not a fair comparison but I'm pretty certain that for some amps at least the improvement in tone as you turn up the volume cannot simply be compensated with EQ adjustments.

BigMonka

I bet the speaker rating plays a part too. I wouldn't have thought that a speaker rated to 100W, with associated stiff cone and big heavy magnet, isn't going to be able to as accurately produce the very small movements associated with a quiet signal.

Cirrus

paulmapp8306 said:

So - does a loud amp sound/react better than a quiet one - absolutely.  Does a RECORDED loud amp sound better than a RECORDED quiet one - to the end listener.... Not really.

I take your point and won't totally argue... but just to pick up on this, I'd sure hate to record electric guitar in a situation where volume limitations are a problem. Assuming a good amp and cab, I've found that there's usually a confluence of a few points;

- Loud enough that the speakers are properly moving and contributing to the tone in a positive way (This ranges from pretty quiet as in a Greenback to pretty loud as in a Vintage 30)

- Loud enough that the wooden cab is resonating, heard as an extra thickness/ bloom in the low end.

- Quiet enough that the power section isn't getting mushy, heard as a reduction in punch, extra fizz creeping in, flabby low end.

Naturally there are exceptions, that's just a generalisation. Usually you're pretty loud to find the point where those factors converge to get the best sound. And depending on the amp of course you might NEED the master up more, like for example an AC30 which has beautiful gain unless you reduce the master volume, then it turns into a waste of money.

nikolas7333

Thanks for the comments. I suppose what I'm trying to get at is, how much of the difference is due to human perception, and how much to something(s) actually changing physically, that could be measured? Surely someone must have at least tried at some point.

ICBM

nikolas7333 said:

Thanks for the comments. I suppose what I'm trying to get at is, how much of the difference is due to human perception, and how much to something(s) actually changing physically, that could be measured? Surely someone must have at least tried at some point.

It's both. There are real sonic differences as you turn the amp up louder - the power stage sometimes goes into clipping (although not always) or at least begins to compress, the amp moves from 'near enough Class A' behaviour to true Class AB, the power supply starts to sag and alter the dynamics, the output transformer bandwidth decreases, the speakers start to thermally compress and cone distortion increases, the cabinet starts to resonate, the reflections from the room increase - but also your ears start to move further up the Fletcher-Munson curve, your body starts to feel the vibrations, and finally your brain starts to get the adrenalin hit from the sheer volume. And that's even discounting increased guitar vibration and near-feedback, as paul said.

But it's certainly not anywhere near as simple as "pushing the power valves harder" as often used as a shorthand for it.

nikolas7333

ICBM said:

nikolas7333 said:

Thanks for the comments. I suppose what I'm trying to get at is, how much of the difference is due to human perception, and how much to something(s) actually changing physically, that could be measured? Surely someone must have at least tried at some point.

It's both. There are real sonic differences as you turn the amp up louder - the power stage sometimes goes into clipping (although not always) or at least begins to compress, the amp moves from 'near enough Class A' behaviour to true Class AB, the power supply starts to sag and alter the dynamics, the output transformer bandwidth decreases, the speakers start to thermally compress and cone distortion increases, the cabinet starts to resonate, the reflections from the room increase - but also your ears start to move further up the Fletcher-Munson curve, your body starts to feel the vibrations, and finally your brain starts to get the adrenalin hit from the sheer volume. And that's even discounting increased guitar vibration and near-feedback, as paul said.

But it's certainly not anywhere near as simple as "pushing the power valves harder" as often used as a shorthand for it.

That's the sort of thing that I was looking for. Thanks a lot for the info.

Bygone_Tones

The speakers are an important part of this, and is probably a major factor in why attenuators do not sound good at super low bedroom volumes. Speakers need a certain amount of beef going into them before they reach that full bodied sound. The amp does not need to be "dimed" as such but speakers will always sound thin and fizzly at very low volumes.

If you want cone distortion they need to be pushed even further.

If you use a 4x12 or 2x12 then all the speakers are sharing the power coming out of the amp, so will not sound as driven as a single speaker on the same volume setting.

ICBM

Bygone_Tones said:

The speakers are an important part of this, and is probably a major factor in why attenuators do not sound good at super low bedroom volumes. Speakers need a certain amount of beef going into them before they reach that full bodied sound. The amp does not need to be "dimed" as such but speakers will always sound thin and fizzly at very low volumes.

I think a bigger reason is that due to the way an attenuator works, when it's set to a very low volume the speaker is much more heavily damped than normal because there is a very low resistance in parallel with it, which restricts the cone movement and makes the sound thin and buzzy.

The reason I think it's this and not the speaker itself is because using a very small unattenuated amp - eg a ZVex Nano - with the same speakers doesn't produce that sound anywhere near as badly. There are *some* speakers which do, a bit - V30s are a good example, I think it's because the surround is heavily doped, which makes the speaker stiffer at very low power input. But something like a Greenback sounds OK at even sub-1W levels.

I agree that most speakers do sound better when they're driven a bit harder though - but they don't have to be thrashed to sound great, in fact really overdriven speakers generally don't sound good to me, even if they survive.

Neckwringer

What a great name for a band..........'The Fletcher Munson Curve'

Lescaster

ICBM;1118325" said:

nikolas7333 said:

Thanks for the comments. I suppose what I'm trying to get at is, how much of the difference is due to human perception, and how much to something(s) actually changing physically, that could be measured? Surely someone must have at least tried at some point.





It's both. There are real sonic differences as you turn the amp up louder - the power stage sometimes goes into clipping (although not always) or at least begins to compress, the amp moves from 'near enough Class A' behaviour to true Class AB, the power supply starts to sag and alter the dynamics, the output transformer bandwidth decreases, the speakers start to thermally compress and cone distortion increases, the cabinet starts to resonate, the reflections from the room increase - but also your ears start to move further up the Fletcher-Munson curve, your body starts to feel the vibrations, and finally your brain starts to get the adrenalin hit from the sheer volume. And that's even discounting increased guitar vibration and near-feedback, as paul said.

But it's certainly not anywhere near as simple as "pushing the power valves harder" as often used as a shorthand for it.

Great post ICBM.

Just reading this post reminds me how much I miss playing through a cranked Marshall.

I remember reading a post on another forum where some people were saying that a kid didn't deserve the Marshall stack and SG he had because he wasn't a virtouso. Others piped up saying that you shouldn't deny a kid the feeling of playing an A chord through a cranked Marshall whilst learning to play because it is one of the best feelings in the world. I agree wholeheartedly.

ThePrettyDamned

Lescaster;1128143" said:

[quote="ICBM;1118325"]nikolas7333 said:

Thanks for the comments. I suppose what I'm trying to get at is, how much of the difference is due to human perception, and how much to something(s) actually changing physically, that could be measured? Surely someone must have at least tried at some point.





It's both. There are real sonic differences as you turn the amp up louder - the power stage sometimes goes into clipping (although not always) or at least begins to compress, the amp moves from 'near enough Class A' behaviour to true Class AB, the power supply starts to sag and alter the dynamics, the output transformer bandwidth decreases, the speakers start to thermally compress and cone distortion increases, the cabinet starts to resonate, the reflections from the room increase - but also your ears start to move further up the Fletcher-Munson curve, your body starts to feel the vibrations, and finally your brain starts to get the adrenalin hit from the sheer volume. And that's even discounting increased guitar vibration and near-feedback, as paul said.

But it's certainly not anywhere near as simple as "pushing the power valves harder" as often used as a shorthand for it.

Great post ICBM.

Just reading this post reminds me how much I miss playing through a cranked Marshall.

I remember reading a post on another forum where some people were saying that a kid didn't deserve the Marshall stack and SG he had because he wasn't a virtouso. Others piped up saying that you shouldn't deny a kid the feeling of playing an A chord through a cranked Marshall whilst learning to play because it is one of the best feelings in the world. I agree wholeheartedly.
[/quote]

I'm lucky to have had that experience.

A few others I think are equally as cool:

Cranked tweed deluxe (that feeling of, "Oh shit, is this going to blow up?!)
Cranked ac30 (I'm Brian May!)
Dual Rec up loud (I'm Linkin Park!)

ICBM

Lescaster said:

I remember reading a post on another forum where some people were saying that a kid didn't deserve the Marshall stack and SG he had because he wasn't a virtouso. Others piped up saying that you shouldn't deny a kid the feeling of playing an A chord through a cranked Marshall whilst learning to play because it is one of the best feelings in the world. I agree wholeheartedly.

I totally disagree.

E is much better .

Uses all six strings .

impmann

Anyone who believes someone doesn't "deserve" a piece of equipment because the owner is not a virtuoso player deserves a punch up the bracket.

Tits.