What is Gain?

USAPatriot

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Here's an interesting question. At least to me.
I have an MXR-108 EQ that I run in the loop of my DSL40C. On one side of the pedal is a slider that says volume. On the other side there's one that says gain. I don't see how the two can be different. What's up with that? -Rod-
 

mickeydg5

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A volume control can be used to describe various types of signal level adjustment.
A gain control is a type of volume control in that it controls the signal level more or less at the input prior to gain blocks. Lower levels will produce less gain which equates to a lower level signal at the output.

The M-108 from what I can tell has gain modules for input, each EQ band and output. So raising the dB of the input will increase overall gain of the unit, which may result in more distortion, whereas the volume slider will only affect what is being output post input and EQ gain blocks.
 

USAPatriot

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That makes at least some sense to me. Could I assume that with the MXR's gain on max, the amount of gain would equal the amount of gain on the amp alone? Volume is basically dry signal pass-thru? -Rod-
 

Leigh

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GAIN-noun- the amount of voltage amplification in the preamp section of an amplifier. This voltage amplification ultimately drives the power tubes which do not add any more gain. The power tubes add current ( power)
 

BanditPanda

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Leigh...that has just confused me ! ( not hard to do ) I thought gain was a term used to describe the over driven or distorted sound which happens when pre amp or power tubes are over driven.
Most prefer the sound of power amp over drive to pre amp tube over drive.
When you say ..."power tubes which do not add any more gain "....when power tubes are over driven do they not produce gain i.e. O/D tones ?
BP
 

Matt_Krush

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Gain (voltage) = Voltage out/Voltage in

Distortion/overdrive isn't always an effect of high gain. You can design circuits to go into saturation/cutoff without much 'gain'
 

fifteenohms

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hey,look....about sustain....someone could explain also the difference about sustain and gain....

Gain is like this: you bump into your chick’s hotter girlfriend, and she remembers you.

Gain with sustain works like this: she informs your gal to give you her number, and she does.

Sustain then is: getting a table for 3 from now on.
 

john hammond

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gain is signal strength.
increasing gain is increasing sparkle,dirt distortion, mud.
increasing volume makes the amp louder.
you can have high gain and low volume, if your amp has some sort of master volume capability
turn up the channel volume on an old marshall jmp, and you turn the volume and gain up at the same time.
put a ppimv on it, and the channel volume becomes a gain knob, and the master volume becomes the volume.
if you have a pedal with ' gain' and ' volume, or level'...2 sliders or knobs, then that's the same thing, one is gain, and the other a master volume.
 
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spacerocker

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GAIN = in the "normal" world = Amplification

You have circuit with a 10mV peak-to-peak signal on the input, and 100mV on the output, you can say that the circuit has a gain of 10 (or 3dB).

Now, the GAIN control on the Pre-amp of a Guitar amplifier DOES NOT alter the GAIN of the circuit. Equally, the Master Volume on the amp DOES NOT increase the gain of the Power amp!


What both these controls do is alter the level of the signal going into those parts of the amp (Pre-amp "GAIN" control alters the signal level going into the pre-amp, MV control alters the signal level going into the Power Amp) The gain of both those parts of the amp is fixed by the circuit design.

The confusion occurs because Guitarists almost always use the term "GAIN" to mean "signal clipping", "overdrive", "Dirt" or "Distortion"

With the "Gain" set low, the signal going into the pre-amp is small, and if the GAIN is low enough, the resulting sound may be clean and un-distorted. But because guitar amps are designed (on the whole) to distort, or clip, as the input signal is increased (by turning up the GAIN control) - the resulting output signal amplitude would be higher than the pre-amp power supply can contain. The result is that the top of the signal is clipped off - clipping occurs! This gives us the overdrive we want, the higher the input signal (from the GAIN pot) the higher the output tries to be, and the more "clipped" or over-driven the sound is!

The same happens with the power amp if the amp is a Master Volume model, then the input to the power amp from the pre-amp goes though the Master Volume pot. This sort of "scales-down" the (possibly over-driven) output from the pre-amp, and sends it into the power section. It is still over-driven, but the MV allows it to be louder or quieter. If the amp is quite powerful, no further overdrive or clipping may occur, but if the MV Pre-amp Gain is high enough, and the MV setting is also high, the signal into the power amp may be large enough to cause clipping in the power section. This adds more overdrive to the sound and us usually considered desirable. However with high power amps, this may not happen until the amp is VERY loud! at lower volumes, most of the clipping and overdrive comes from the pre-amp!

So the GAIN control does NOT alter the gain of the amp. But it does affect the level of clipping or overdrive in the pre-amp! If we think of GAIN = Overdrive it all makes sense! It's another case of technical terms being mis-used in the guitar world - e.g. "Vibrato arm" on a Fender is (mis) called a "Tremelo"!

Here's another one for you - the accelerator on a car is NOT a speed control - it is a "Torque demand control" !
 
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mickeydg5

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Just to throw this in, the very definition of gain here is the actual "gain" in signal level from one point to another.
The potentiometer or other signal/volume control device whether called GAIN, PREAMP VOLUME, VOLUME, MASTER VOLUME, PPIMV, VVR, EPA, POWER SCALING or something else still controls the "gain" of the amplifier.

Anything that controls the signal level is a gain control.
 

spacerocker

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Just to throw this in, the very definition of gain here is the actual "gain" in signal level from one point to another.
The potentiometer or other signal/volume control device whether called GAIN, PREAMP VOLUME, VOLUME, MASTER VOLUME, PPIMV, VVR, EPA, POWER SCALING or something else still controls the "gain" of the amplifier.

Anything that controls the signal level is a gain control.

I see what you are saying - but in electronic terms, GAIN does not equal "an increase from one point to another". it means the multiplication factor of a circuit.

Suppose we have a circuit where for an input signal of 1V Peak-to-Peak, the output is 2V Peak to Peak. That circuit would have a gain of 2.

Now suppose we increase the input to 2V. The output will have gone up to 4V. Does that mean we have increased the gain? NO - because the gain which equals output voltage divided by input is still 2.

If we have a so-called "GAIN" pot on the input of the circuit I described above which can be turned up or down to control the signal level going in, then that pot is NOT strictly a GAIN control, as the GAIN of the circuit stays the same, irrespective of the level of the input!

A true GAIN control would increase the output of the circuit even if the input stayed the same

So I disagree with this statement "The potentiometer or other signal/volume control device whether called GAIN, PREAMP VOLUME, VOLUME, MASTER VOLUME, PPIMV, VVR, EPA, POWER SCALING or something else still controls the "gain" of the amplifier." - even though this is a common mis-conception!
 
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mickeydg5

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That makes at least some sense to me. Could I assume that with the MXR's gain on max, the amount of gain would equal the amount of gain on the amp alone? Volume is basically dry signal pass-thru? -Rod-
No. Every device has its own design, input levels and output levels. You can control the gain of the device with the controls. When it is maxed out that is all it can give.
 

mickeydg5

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I see what you are saying - but in electronic terms, GAIN does not equal "an increase from one point to another". it means the multiplication factor of a circuit.

Suppose we have a circuit where for an input signal of 1V Peak-to-Peak, the output is 2V Peak to Peak. That circuit would have a gain of 2.

Now suppose we increase the input to 2V. The output will have gone up to 4V. Does that mean we have increased the gain? NO - because the gain which equals output voltage divided by input is still 2.

If we have a so-called "GAIN" pot on the input of the circuit I described above which can be turned up or down to control the signal level going in, then that pot is NOT strictly a GAIN control, as the GAIN of the circuit stays the same, irrespective of the level of the input!

A true GAIN control would increase the output of the circuit even if the input stayed the same

So I disagree with this statement "The potentiometer or other signal/volume control device whether called GAIN, PREAMP VOLUME, VOLUME, MASTER VOLUME, PPIMV, VVR, EPA, POWER SCALING or something else still controls the "gain" of the amplifier." - even though this is a common mis-conception!
Multiplication factor is built into the equation of a component's gain.

I see what you are getting at with the above. If you have a fixed gain/amplification factor then the output would be that times the input for that component.

The problem with that thinking is that you are not including the input and output loads being varied by the controls, the potentiometers. A load change on the device changes the gain of that component, that stage.

Controls like a potentiometer cannot increase anything. They can only attenuate, decrease, diminish.

So like you mentioned above when you "scale down an output" or signal then you are effectively decreasing the gain of the device/unit.
The gain of a unit/device:
input 300mVAC, output 300VAC, gain = 1000
input 300mVAC, output 30VAC, gain = 100
The differences in output are caused by variation of controls and the circuits themselves.
 

spacerocker

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I think we will have to agree to disagree on this one. You almost agree with me, but......

Multiplication factor is built into the equation of a component's gain.

I see what you are getting at with the above. If you have a fixed gain/amplification factor then the output would be that times the input for that component.

Agreed. The "multiplication factor" (i.e. the Gain) is set by the components in the circuit (e.g. the type of valve) and the components around it (e.g. Cathode resistor, etc..), NOT by the input signal strength (amplitude)

The problem with that thinking is that you are not including the input and output loads being varied by the controls, the potentiometers. A load change on the device changes the gain of that component, that stage.

Whilst I agree that the load on the amplifier stage may have some small effect on the gain (and in linear gain stages, negative feedback reduces this effect), but he load from the subsequent stage stays the same - the so-called gain controls we are talking about are potentiometer at the INPUT of the pre-amp stage, power amp stage etc. Whilst they can vary the voltage into that stage the input current does not change much due to the high input impedance of a valve, so the gain stays almost completely the same. The GAIN control only increases the output because it increases the input!

Controls like a potentiometer cannot increase anything. They can only attenuate, decrease, diminish.

Agreed. They are passive components. I don't think I said anywhere that a potentiometer can increase a voltage?

So like you mentioned above when you "scale down an output" or signal then you are effectively decreasing the gain of the device/unit.

No. I was talking about the master volume pot. This scales down (i.e reduces) the signal from the pre-amp prior to going into the power amp. We are not decreasing the gain of the pre-amp, just reducing the amplitude of its output. The Pre-amp gain stays the same (as does the power amp gain).


The gain of a unit/device:
input 300mVAC, output 300VAC, gain = 1000
input 300mVAC, output 30VAC, gain = 100

Here, you agree with me. Gain is output divided by input. But here you would have to be either talking about two different devices, or altering the circuit by changing the value of external components (e.g cathode resistors, etc) Marshall Amps do not have controls to allow you to do that.



The differences in output are caused by variation of controls and the circuits themselves.

Agreed. The output is varied by the level of the input x the gain of the stage. The fundamental gain of the circuits cannot be changed by the controls on the amp. i.e. the "Gain" and Master volume controls can control the level of overdrive , and the overall volume of the amp. But the GAIN of the pre-amp and Power amp stages are unchanged. To look at in another way, with pre-amp GAIN, Channel Volume, and Master Volume up FULL (i.e. the amp flat out) you have the natural gain of the whole amp. Turning any of those controls down, just attenuates the signal at various points to make the amp quieter/less over driven etc....The GAIN control sets the level if signal INTO the pre-amp, the channel VOLUME (for multi-channel amps) pot sets the level of output from the pre-amp into the power amp, and the MASTER VOLUME pot sets the signal level into the power amp. None of those controls change the fundamental gain of those stages!

Final thought - to change the GAIN of a circuit, you have to change the characteristics of an active circuit (i.e. valve, transistor, etc...) This can only be done by changing external components (cathode current, feedback resistor, etc) changing the input level (e.g. using a potential divider) does not affect circuit characteristics like gain, etc
 
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mickeydg5

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@spacerocker
I agree with lot of what you posted.

I was just pointing out that the gain of a unit/device versus that of a component are different things, looked at a bit differently.

All I am trying to say is that the Mu/Amplification factor and the Gain/Voltage Amplification are not linear. Those change as the circumstances vary around the amplifying component.
AC signal strength/level input as well as AC load on the amplifying component affects its operation. A small input signal and greater load will decrease its efficiency, its amplification factor and its gain. It is a reactive component and has a gain curve.
 
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spacerocker

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@spacerocker
I agree with lot of what you posted.

I was just pointing out that the gain of a unit/device versus that of a component are different things, looked at a bit differently.

All I am trying to say is that the Mu/Amplification factor and the Gain/Voltage Amplification are not linear. Those change as the circumstances vary around the amplifying component.
AC signal strength/level input as well as AC load on the amplifying component affects its operation. A small input signal and greater load will decrease its efficiency, its amplification factor and its gain. It is a reactive component and has a gain curve.

Yes - I get what you are saying, and I think we kind of agree?

I know gain can vary a bit depending on the signal strength, but I like to keep things simple, especially on forums and it is almost splitting hairs to say that the "GAIN" knob increases gain because the gain characteristics change slightly with a larger signal..90% of the reason the output from the gain stage gets louder/more distorted (depending on whether it is power amp or pre-amp we are talking about) - is simply because the input gets bigger, and the ouput is GAIN x Input....

I would hazard a guess that most people (and I used to be one of them until about 10 years ago!) think that the GAIN control actively changes the gain by modifying the gain setting part of the circuit - not just by varying the input level to a (mostly) fixed gain circuit. That's the point I was trying to make, really!
 


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