Would someone please explain how 'gain' functions?

Gain is the ratio of the output voltage of a component to its input voltage. In the case of a preamp or a line stage or other component having a volume control it is usually defined based on the volume control being set to its maximum position. It can be defined either as a numerical ratio (e.g., 100 times), or in db (db = 20 x logarithm(Vout/Vin); 100x = 40 db).

Usually a CD player or DAC or other digitally-based source component will provide higher output voltages than most phono stage/cartridge combinations, and so the resulting volumes will be different unless the line stage provides independently adjustable level settings for each input.

A factor that can dramatically affect perceived loudness is the dynamic range of the recording, and consequently how much dynamic compression it has been subjected to when it was engineered. Our hearing mechanisms tend to sense volume based on the average level of what is heard, rather than on brief dynamic peaks in volume or on passages that are significantly lower in volume than the average. So if everything else is equal (including the volume control setting) if a recording that has been compressed to a narrow dynamic range (i.e., so that a relatively small difference in volume occurs between the loudest notes and the softest notes) it will tend to sound louder than if the same music has been engineered with minimal or no dynamic compression.

Also, of course, recordings can differ somewhat in the overall volume levels they have been mastered at, even if the music and the amount of dynamic compression are similar.

Regarding phono stage gain, depending on the particular phono stage and cartridge, as well as on the gains and sensitivities of the downstream components including the speakers, there will usually be a relatively small range of phono stage gains that will result in an optimal balance of sonics, noise levels, volume control positions, and avoidance of any possibility of overloading either the phono stage or the preamp. Too much gain or too little gain can adversely affect some combination of these factors.

Regards,
-- Al

@Inna, you may be aware of the rule of thumb guideline that a 10 db increase in volume corresponds subjectively to "twice as loud," and correspondingly a 10 db decrease corresponds subjectively to "half as loud."

To provide some additional perspective, for a preamp or integrated amp having a rotary volume control whose minimum position is approximately at the 6:30 o’clock position, and whose maximum position is approximately 5:30 o’clock, a 6 db change will probably correspond to around 45 degrees of rotation. Assuming, that is, that the control is not in the lowest 20% or 25% or so of its range, where volume changes usually occur more rapidly as the control is rotated.

Regards,
-- Al

@N80, I would think the manual should and hopefully would answer that.  Or if not, a call or email to the manufacturer would seem to be in order.

Regards,
-- Al  

1) Assuming a speaker is not being overdriven to the point where its behavior becomes significantly non-linear (i.e., "thermal compression" becomes significant), voltage db at any point in the electrical signal path and SPL db produced by the speaker at a given distance will be proportional.

See this writeup for a description of the reference level for SPL db.

2) As I mentioned earlier some preamps provide independently adjustable input level controls. Many and probably most do not, presumably because they would add complexity and cost, and perhaps compromise sound quality. And the user can simply adjust the volume control setting when selecting among different source components.

4) Yes to the statement. Perhaps to the question.

5) Yes.

6) Professional computer-based audio editing programs can easily change the ones and zeros to different ones and zeros corresponding to compression parameters specified by the user.

5) The gains provided by the electronics will not be affected, at least to a degree that is audibly significant. Under some circumstances temperature variations could conceivably affect their gains to at least a slight degree, though. I’m not sure how or if acoustic SPLs might be affected.

Regards,
-- Al