Re: Thoughts about amplifiers at 3/4 volume.
Sending a hot signal and padding down the input at the amp, will reduce noise picked up in that interface between amp and the sending unit. This is less of an issue with good modern balanced inputs, balanced sends. and balanced (3 circuit XLR) wiring. In the not so good old days, using unbalanced interfaces and wiring, it was a very valid technique to manage noise in quiet ambient venues (like HOW). I can imagine a modern venue with distro or whatever issues and hum in the amps, that might benefit from hot level and pad, but with clean interfaces, not so much.
So arguably with modern gear you "should" be able to get by without amp trims, but there is a lot of inertia in the marketplace so customers will still want their amp trims for some time to come, and there could be the occasional problem gig where this technique could help.
JR
