Many quality preamps have been designed to remain powered on, in some fashion. I would check on CD, etc, players as many have standby features. I always liked to have mine playing well before I listened. However, exceptional power conditioning for my CD player has made such a dramatic difference to sound quality I'm now ok with the sound from standby, and haven't felt the need to further evaluate. The conditioning resulted in spectacular improvement; far more than any warm up. With SS amps manufacturers often have a recommendation. Don't forget all items that heat up also wear out/degrade over time.
power supply
How often do we have to turn off our equipment such as power amp , pre amp. cd player , power conditioner ......? Can we leave them on for days while listening on and off or do we have to turn them off after every session of listening? As a general rule the more the systems are left on the better the sound , so what is your idea on this issue ?