Kennyt:
I know that the Carys' HT bypass works when the unit is powered off. They default to HT bypass automatically. I cannot speak for the others on this list.
The benefits of "powered off" HT bypass:
1) Saves on tube life if it is a tube pre. Not a big difference, but a difference nonetheless.
2) Saves on electricity. Same idea as #1.
3) Saves on heat. Same idea as #1 and #2.
4) Prevents possible ground loop hum from being introduced into HT system by having it interact with the preamp while it is on. I have experienced this before.
5) The security of knowing that the preamp is not processing the HT signal at all. Some might prefer that, but I do not.
I know that the Carys' HT bypass works when the unit is powered off. They default to HT bypass automatically. I cannot speak for the others on this list.
The benefits of "powered off" HT bypass:
1) Saves on tube life if it is a tube pre. Not a big difference, but a difference nonetheless.
2) Saves on electricity. Same idea as #1.
3) Saves on heat. Same idea as #1 and #2.
4) Prevents possible ground loop hum from being introduced into HT system by having it interact with the preamp while it is on. I have experienced this before.
5) The security of knowing that the preamp is not processing the HT signal at all. Some might prefer that, but I do not.