Well the appropriate pre-amp gain depends on the source that you are using (how many V does have the signal that is coming in) and on the power amp that you are using - how much gain does it produce.
If you are using a CD player with 2 V output (nearly a standard nowadays) and you have power amp with 30 dB gain then you do not need huge gain from pre-amp. Several dB will be sufficiant; let's say 4 dB or 6 dB. If you are using a source with lower V output (tuner, ...)and you have an amp that has 20 dB gain, then it may be necessary to have pre-amp gain of mentioned 15 dB.
So it has to be judged in the context of one concrete set-up. I do not believe that there is a generall answer on your question. There though pre-amps that have adjustable gain (Pass Labs X 2.5 is one of them) so you can change the gain level in the pre-amp. This brings additional flexibility to the pre-amp and is certainly interesting feature.
Regards
Dejan
If you are using a CD player with 2 V output (nearly a standard nowadays) and you have power amp with 30 dB gain then you do not need huge gain from pre-amp. Several dB will be sufficiant; let's say 4 dB or 6 dB. If you are using a source with lower V output (tuner, ...)and you have an amp that has 20 dB gain, then it may be necessary to have pre-amp gain of mentioned 15 dB.
So it has to be judged in the context of one concrete set-up. I do not believe that there is a generall answer on your question. There though pre-amps that have adjustable gain (Pass Labs X 2.5 is one of them) so you can change the gain level in the pre-amp. This brings additional flexibility to the pre-amp and is certainly interesting feature.
Regards
Dejan