High end preamps (and DACs, phono stages and streamers)use every design trick to lower the noise floor and create a quiet stable power supply. This entails massive power supplies and mass to dampen vibration. I think the average of my components is around 40 lbs... Phono Stage, Preamp, DAC, and Streamer.
I can honestly say that over the last fifty years I have never heard a great light weight audiophile component. After a while, I would always check out its weight before choosing to listen to something. If it didn’t weight a lot... I wouldn’t bother (unless highly reviewed... and every one failed to impress me). Typically the sound quality varies with the weight. However there are some heavy components that don't sound good. So you can't choose by weight, I choose by the sound. But you can eliminate the stuff that is not likely to sound as good that way.
I have a friend in the business and asked if he had ever heard a great piece of gear that was light weight... he could only think of one. He was a dealer going to shows every year, selling for over 25 years.

