The problem with the TP pre's, as well as the R-115 and 117 is, they all have a "soft start" power switch that isn;t a in-out power switch..
They can't be used with timers for instance, which is why I replaced the 115 in the bedroom with the 113 that does have a dedicated in-out power switch (and arguably, better sound than even the 115) to use falling asleep and turn the radio on in the morning.