Yes, thanks for that khaine1711.
As an aside....
Steve Deckert (of Decware) produces a little 12AU7-based variable-gain tube buffer called the ZSTAGE, which he designed to be inserted in between a DAC (or pre-amp) and the amp, for the express purpose of changing the sound signature by varying the ratio of gain provided at the amp's inputs vs. gain provided at the amp's outputs.
Quoting the Decware ZSTAGE Owner's Manual:
RIDING THE GAIN - A term we came up with because of the active nature of the adjustment process that can take place when you use a ZSTAGE in conjunction with an preamp OR ampliﬁer ﬁtted with a gain control.
Riding the gain happens when you have two controls. One at the source and one at the amp or preamp. Think of it like water pressure. You have a pipe with a valve at the input end and another valve at the output end. The valves represent the gain controls and the pipe represents the signal path between the two gain gain controls. By turning up the input valve and turning the output valve down we create pressure inside the pipe. By turning down (closing) the input valve and turning up (opening) the output valve we reduce pressure inside the pipe. So if you took a garden hose and turned on the faucet you would have lots of water coming out the end, but it wouldn’t be able to spray anything until you put a nozzle on the end. The nozzle acts like a valve to restrict the output causing the pressure in the hose to increase. PRESSURE in this metaphor is the same thing as DYNAMICS in your stereo system.
By having a gain control at the source and a second one at the amp (or preamp) it is possible to manipulate the dynamics of your music and it’s overall frequency balance. For example, if the music sounds thin you can increase the “pressure” by turning down the gain control on the ampliﬁer (or preamp) and then raising the gain control at the source. This will add noticeable weight to the music and mellow out the top end. On the other side, if the music is sounding boomy or thick, you can do the opposite - turn up the gain on the amp and reduce the gain at the source. The boominess will go away.
So it seems the ZSTAGE, having an adjustable output in the range 1 to 5 Vrms, can reduce dynamics by reducing the Vrms supplied to your amp's inputs (as you increase the gain at the amp's volume control to maintain a constant SPL at the headphones) -OR- it can increase dynamics by increasing the Vrms coming into the amp (as you decrease the gain at the amp's volume control to compensate).
This leads me to conjecture that a line-level attenuator would reduce dynamics at any desired SPL, while resistors placed at the amp's outputs would not. In other words, don't use line-level attenuators if you want to avoid flattening the dynamics.
What do you think?