Why some preamps weigh 50+ lbs?

Then you have passive pre-amps….

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. 

The collective weight of parts used equals the weight of the unit. Hope this helps.

Mine weighs 53 lbs and has two chassis. It takes 8 tubes and a lot of space. The mono amps each weigh 45 lbs and have 7 tubes each. Looks cool and sounds pretty good. One thing for sure is with 22 tubes it’s one heck of a good space heater ! This way I can hear my electricity being used. I just wanted to inject some humor. Happy Thanksgiving to all, Mike B. 

I asked that question when I got an All Clad copper core sauce pan, when I compared it with my Hexclad pan. Stopped after using it for the first time.