Basic amp Qs Volume/ gain/ MV.

[Sea Chief]

You listed the different types of volume controls in the same order that they appear in the signal chain, and that is what determines their effect.

The earlier the volume control is in the signal chain, the more it tends to control the amount of distortion, as opposed to the volume..

OK! thats clear I think.

The later the volume control is in the signal chain, the more it functions like a real volume control, controlling the volume you hear in the room without affecting the amount of distortion.

I sort of undertand this: I cant quite distinguish in practise tho it seems between my gain controlling the overall volume, and my overall volume doing so.. but can at least see some logic to this, in theory.

This distinction can only be seen if some stage of the signal chain is distorting. If the signal is completely clean, nothing is distorting, then all of the volume controls do the same thing..

Im sorry I dont understand this (what distinction? between x and y there is usually a distinction but you mentioned prior to this only one parameter that being 'volume'). Or if all of the volumes do the same thing if the signal chain is clean- surely the clean signal can be distorted by turning up any one [high] whether its 1( 2,3,4 or 5) of the various volume knobs-?

If most of the distortion comes from one stage in the signal chain, then all volume controls before this stage will function as "amount of distortion" controls and all volume controls after it will function as regular volume controls. You can easily verify this for yourself with a distortion pedal...

Totally confused- can we not simplify things to a preamp stage, and a pwr amp stage!? any more bloomin 'stages' than 2 and my brain aches (I thought any amp inherrantly has just a preamp, and a pwr amp stage anyway!)

The problem you have is that the 5E3 generates much of its distortion in the last two stages of the chain: the PI and power tubes. There is no convenient way of placing a volume control after these

So that is a 3rd 'stage' called a phase-inverter I believe? (but not there on a simple Champ is it?) so this extra stage means automatically an extra volume knob? its own volume knob? none, or optional? crikey O Reilly. So does a "gain" knob go before this PI, and a "volume" knob go after it? or is a "gain" knob simply another word for a "volume" knob? or is a "post-vol" knob reference to this PI stage'??? jesusH. I need a lie down.

[Sea Chief]

I need to go right back to square 1.

1. Can anybody tell me what the difference is between a "gain" volume knob, and a "pre" volume knob. Or are they the same thing?

2. Am I correct in my analogy of this "gain" volume knob -if up high- is akin to the input signal/GTR vol "AT LEVEL 20, AS IT WERE" ?

I need to go from here and distinguish between this and the next vol knob along the 'signal chain' (whatever exactly this is, or along the 'stages' is it? are these the same thing?).

thx SC

[Jazz P Bass]

I think that you need to research how an amplifier works.
What Steve said is as clear as a bell.
Preamp, Phase Inverter & Output section is a typical lineup, block wise, of a push pull amplifier.
The 'Gain' control adjusts the signal amplitude in the preamp.
Hit the preamp with a tall (amplitude) enough signal, & if the circuit cannot handle that height, it will distort the signal.
If the signal height stays below the distortion threshold, the signal will be clean & undistorted.
Your guitar volume control is a gain control.
The phase inverter amplifies nothing.
It's sole purpose is to provide a push & a pull signal to the output tubes.
The output stage provides current to the output transformer.
The only 'Volume' control in all of this would be after the preamp.

[Sea Chief]

Hi Jazz P Bass.

Ok look you say the 'GTR volume control is a gain control' ..but that 'The only 'Volume' control in all of this would be after the preamp'. Eh? ok so look, what if the amp has a 'Gain' control? is that -not- a volume control then? (surely the same as the gtrs volume control you say IS a gain control?)

You can you see why Im confused surely?

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I need to go back to sq1. Pls what the difference is between the following on an amp..

[1st lot] Ok, the controls usually near or next to the input jack I see variously named as (I can only imagine they -must- have different names for the same thing) GAIN, or VOL, or DRIVE, or PRE VOL.
[2nd lot] I then occasionally see a control named POST VOL usually next along rhs or thereabouts, or I may simply see again the word/ control named VOL.
[3rd lot] Thankfully the last control is often called simply VOL or MASTER (I assume these to be the same/ I hope to god they are).

I need to establish if the [1st lot] these are A) all the same or B) not neccesarily & so If not then separate them -hopefully- no more than TWO lots of the same thing. Then I need to distinguish the difference between these.

[eschertron]

I need to go right back to square 1.

1. Can anybody tell me what the difference is between a "gain" volume knob, and a "pre" volume knob. Or are they the same thing?

2. Am I correct in my analogy of this "gain" volume knob -if up high- is akin to the input signal/GTR vol "AT LEVEL 20, AS IT WERE" ?

I need to go from here and distinguish between this and the next vol knob along the 'signal chain' (whatever exactly this is, or along the 'stages' is it? are these the same thing?).

thx SC

Which is why, I think, that Orange has only little pictures instead of words. I might want more distortion, so I'll turn up the 'Hammer' and turn down the 'Ear' for example (disclaimer: not descriptions of actual Orange copyrighted pictures).

Technically, all the knobs we've discussed are gain knobs. Volume is something done with hair. Pre- and post- are meaningless terms absent the device they are referencing. So forget the names of the things, and focus on where they happen in the signal chain (as Steve outlined above). Now every one of them will cause the signal to get louder, because we are turning up the amplitude of the waveform. Whether it distorts or not is determined by the design of the amp, and the level of the signal. Fender amps can get REALLY LOUD before they distort, if they distort at all. This because only the last stage (the power tubes) are likely to be overdriven. If that's the sound you want, then, well... crank it up. Use a power attenuator (power soak) to reduce the amount of energy going to the speakers, but be prepared to hear the sound differently than before.

All these concepts have been described and discussed above. Review the concepts as things become clearer to you.

[Sea Chief]

Thanks. I have read, and read and read again. But, with different names afaict that affect the volume, and therefore have to be volume controls of sorts, I must surely try and distinguish between them.

That is all Im trying to do. Im not at this moment in time needing per se to understand more technical processes like amplitude, waveforms and clipping/ the mechanics of distortion. That will be compared to this, for me, relatively even -much- more simple.

All I know is there is a vol usually at the end (MV or VOL) and one (or two or even three) usually at the beginning. All affect the volume, so all must be or sorts volume controls. But they can be called different things "gain" or "Drive" or "pre Vol" just "vol" for eg. I think my confusion -may- be compounded by the same volume control knob (esp this 1st one) called by different manufactures &/or models etc, different names. Or if not god help me, I am determined & I will simply understand the differences between them.

[eschertron]

Thanks. I have read, and read and read again. But, with different names afaict that affect the volume, and therefore have to be volume controls of sorts, I must surely try and distinguish between them.

That is all Im trying to do. Im not at this moment in time needing per se to understand more technical processes like amplitude, waveforms and clipping/ the mechanics of distortion. That will be compared to this, for me, relatively even -much- more simple.

All I know is there is a vol usually at the end (MV or VOL) and one (or two or even three) usually at the beginning. All affect the volume, so all must be or sorts volume controls. But they can be called different things "gain" or "Drive" or "pre Vol" just "vol" for eg. I think my confusion -may- be compounded by the same volume control knob (esp this 1st one) called by different manufactures &/or models etc, different names. Or if not god help me, I am determined & I will simply understand the differences between them.

Exactly! No two manufacturers use these names to mean the same thing. Even when they have circuits that are similar, they may call the same control by a different name.

[RANT]There is no absolute consistency in the naming, especially when more than one control appears on a given amp. If you dig into the history of the development of guitar amps over the decades, maybe it will become clearer about WHY different (and yes, confusing) names are given to the knobs. Don't get hung up on what it's called. Understand what it does ON THE AMP IN QUESTION. What it does on amp X has no bearing on what a a knob with the same name does on amp Y.[/RANT]

Yes, there are a few general trends that can be observed. For example, the 'Master Volume' almost always comes before (or after. See, the rule is already broken) the phase inverter section and usually (broken again!) has the effect of controlling overall loudness on the amp. History tells us that it was added to some 100W monsters in the late 60s to get the distorted sounds that were desired without the ear-killing loudness. Did it work? Still up for debate...

On your Fender amp, the distortion comes mostly after the master volume. So does the MV work? Not the way you tend to use it. Can you make it work better than 'not at all'? Yes. You could put a pedal in front of the amp to overdrive the preamp section, and turn down the master to keep the loudness under control. The pedal between the guitar and amp becomes another "knob" to turn up. It's just a knob. Turn it up, and if the sound of the pedal driving your preamp appeals to you, then the master volume (at the end of the signal chain) can function in the way you intuitively want it to. That is, to control the loudness (volume) of the sound in your performance space.

[Steve Conner]

Im sorry I dont understand this (what distinction? between x and y there is usually a distinction but you mentioned prior to this only one parameter that being 'volume').

The distinction between volume controls near the beginning of the signal chain that control the amount of distortion, and volume controls near the end that control the loudness.

Or if all of the volumes do the same thing if the signal chain is clean- surely the clean signal can be distorted by turning up any one [high] whether its 1( 2,3,4 or 5) of the various volume knobs-?

No. I said that the volumes all do the same thing in the absence of any distortion. Once distortion starts to happen, the reasoning you used to derive this statement isn't valid any more. The behaviour of the system changes, any volume controls before the distorting stage control the amount of distortion, and any volume controls after the distorting stage control the volume.

any more bloomin 'stages' than 2 and my brain aches (I thought any amp inherrantly has just a preamp, and a pwr amp stage anyway!)

A Champ has 3 stages of amplification. (Two preamp triodes and a power tube.) The volume and tone controls are between the 1st and 2nd stages.

A 5E3 has 4 stages: two preamp stages, a phase inverter and a push-pull pair of power tubes. Again the volume and tone controls are between the 1st and 2nd stages.

A master volume Marshall has 5 or 6 depending whether you count the cathode follower as a "stage". The knob that Marshall called "preamp volume" is between stages 1 and 2, and if we say it has 6 stages, then the master volume is between stages 4 and 5.

No wonder your brain aches.

So does a "gain" knob go before this PI, and a "volume" knob go after it? or is a "gain" knob simply another word for a "volume" knob? or is a "post-vol" knob reference to this PI stage'??? jesusH. I need a lie down.

Referring to my original post: The kinds of volume knobs that live near the beginning of the signal chain and mostly control the amount of distortion are given names like "gain", "drive" and "pre volume". Except for the guitar volume control, which is still called "volume" for traditional reasons even though it turns into a gain control as soon as you start using distortion.

The ones that live near the end and actually control volume get names like post volume and master volume.

[Sea Chief]

eschertron much obliged for that post.

Yes of course the best way is simply sit with the amp and play with the volume(s) and see simply what it does to my ears. The thing is, why Im trying to crack this BIG nut as I find it to be (simple to you lot) is that Im not in a position to 'go try a few amps' as I live rurally, and literally quite often 'just plump for a s/h amp from the usual places.' But without up till now really understanding exactly what these controls are -likely- to do in principle.. I keep getting entirely the wrong amp. So now I need to see what labels are put on amp X's volume controls, and find out what exactly they are fundamentally, then I have a good page 1 idea of the sound I want. Then I can narrow down/ shrug off... & get a good amp.

So you've helped clear my brain up somewhat there. But Im -still- sort of guessing somewhat too; ie I think/ I have the notion/ that there is likely to be solely one volume at the end (of the control panel usually) an 'overall volume' & one (or two: now you see its ---this--- which Im still not clear about, ie ----what is the difference between this and the adjacent volume control, both I think, in the preamp/ input area of the amp/ ie usually situated adjacent to the input jack----?). It is the *interaction between these* I need to understand, whatever they might be called by the amp-maker on the control panel *AND therefore both their interactions with the master volume* at the far end of the control panel. There must be some rules of thumb I am desperately seeking, there just must be, regardless of their actual silkscreened wording on their respective knobs.

IE I might have a Blues Jr with controls from LtoR [input] VOL. mid. bass. something. other. MASTER.
And I might have a Vox diddy head thingy. [input] GAIN. mid. bass. something. other. MASTER.
And my Bandit65 (fab ss) [input] PRE VOL. s'thing. POST. eq. knobs. but no vol last. REVERB.
Or if I see [input] GAIN. VOL. VOL. eq. knobs. DRIVE. other. crap. MASTER. (then I dont know wtf is going on!!).

Thats a good eg of my confusion with this: 3 egs each having all sorts of places, knobs, and variations of the volume controls. Its like having a car with 'oh yes with this one the gear stick is between your legs' and the next 'this car has one in the door and on the normal spot, you have to figure it out'. The 3rd car has the gearstick 'in the dashboard- you have to use it -with- an extra 4th pedal on this car'.

It makes my brain hurt.

[Jazz P Bass]

[QUOTE=Sea Chief;316022]Hi Jazz P Bass.

Ok look you say the 'GTR volume control is a gain control' ..but that 'The only 'Volume' control in all of this would be after the preamp'. Eh? ok so look, what if the amp has a 'Gain' control? is that -not- a volume control then? (surely the same as the gtrs volume control you say IS a gain control?)

You can you see why Im confused surely?

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QUOTE]You cannot process what you are reading.
You took a perfectly clear explanation that I gave & twisted it up.
Simply stating that the guitar volume control (which is what it is called) is actually a gain control, as far as the preamp is concerned, should have been enough to 'unconfuse you'.
Low preamp gain, low distortion.
High preamp gain, distortion.
I have had quite enough of this lame post.
I think that you are 'trolling'

[Enzo]

SC, think about driving a car. You can give the engine a lot of gas in a low gear and drive at a certain speed, or you can give the car less gas, but in a higher gear and drive the same speed. And of course more gas AND higher gear means car goes faster. But any one factor doesn't necessarily make speed. Now your amp: assume each stage of the amp has a volume control. You can turn the early one up and the later one down and play at a certain loudness. Or you can turn the early one down and the later one up and have the same volume. Just having more controls does not necessarily make more volume.

In your amp though, turning up the earlier controls is more likely to cause the signal to distort. SO the early up and later down will likely be more distorted than the other way around. A little experimentation ought to demonstrate the effect of each control.


Don't obsess over the names of the controls, we have to call them SOMETHING after all. If we called them all just volume, it would be very confusing. Gain just means the amount of amplification. If I put in 5 and get out 20, we amplified by 4. A stage is nothing more than a step along the circuit, in a tube amp, it means each tube section, like the triodes of a 12AX7. SO if the signal path goes through three triodes in the preamp, those are three stages. With certain exceptions, each triode amplifies - has gain. And they accumulate. If I took that circuit with a gain of 4, and fed it a signal of 5v, then I get 20v out. If I then feed that 20v into another X4 stage, I'd get 80v out, and so on. You are limited only by the available voltage and ability for a signal to be handled. In the above example, if my circuit only runs on 50v, that second stage cannot make 80v of signal, and so is distorted.

You can add a volume control anywhere you like, between every stage if you wanted. Such a volume control does not add amplification, in fact it can only reduce the signal at that point. So a lack of a volume control at any point is the same as having one there all the way up.

Technically, gain is the amount of amplification, while volume is the amount of signal. SO your guitar knob is a volume control, as are most tube amp controls. We all misuse the term "gain" all the time. But that's OK, we'll use gain and volume interchangeably. Everyone else does. Pre and post means where in the signal path something is. Post means after, so a post gain means a control after the bulk of the preamp. And a pre gain means before the bulk of the preamp. On some other amp the pre might be called drive - it controls the amount of signal driving the preamp. Post might be called level. On an amp with a clean and a dirt channel they might call the clean controls volume and the dirt channel controls gain. That just makes it easier to know which knob they are talking about. And master means nothing more than it is the last control in the chain. It is master because it controls the volume of whatever was coming out of everything else.

[Dave H]

Perhaps a picture will help?

The schematic below is a typical Master Volume amplifier.

A1, A2 and PA (Power Amp) are the amplifier stages.
VR1 is the gain control near the input. It could be called Gain, Vol, Drive etc. It doesn’t matter.
VR2 is the gain control near the power switch. It could be called Gain, Vol, Master Vol etc.
The guitar does not have enough output to overdrive A1

It could be set up like this -
Set your guitar vol to 10.
Set VR2 to a low level so as not to blast your ears (or overdrive the power amp).
Turn up VR1 to overdrive A2 to the max required distortion level (not volume level).
Turn up A2 for the required volume level (loudness).

The guitar vol will now work like turning down VR1 but be in a more convenient place.
Tuning it down from 10 will first reduce the distortion, then clean it up, then reduce the clean volume.

Make sure you fully understand the above before continuing.

In the above example the power amplifier is not overdriving. All the distortion comes from overdriving A2 which you may not like as you prefer power amp overdrive. To get power amp overdrive turn up VR2 to max to turn the amp into a non master vol amp (non master vol amps only have VR1). Turn up VR1 to get the required level of power amp distortion. A2 will not distort as it now passes the signal directly to the power amp. You will now notice that it is distorting nicely but it is too effing LOUD! And you can’t do much about it without cleaning it up because both the guitar vol and VR1 are before the overdriving stage (power amp) so turning them down reduces the overdrive. One way to overcome this is to put an attenuator between the power amp and the speaker and use this exactly as VR2 was used in the first example. This will change the sound compared to the un-attenuated amplifier which you may not like.

You don’t like the attenuated sound you say? We will now go on to discuss VVR circuits and Isolation Cabinets. Like hell we will. I need a beer