Amps on top?

Yes, it’s nice to have the weight low in a rack, helps stabilize, and avoids a high fulcrum point when up top. Especially with flexible wood floors like mine. Perfectly level is your friend when weight is high.

I have my heavy amp and my heavy R2R deck on two separate cabinets to the left and right of the equipment rack for several reasons. AND felt on the bottom of the cabinets so I can spin the cabinets individually to access jacks/cables.

If you look at my virtual system

https://www.audiogon.com/systems/9511

I made a ’ventilated stand’ to put the preamp on that cabinet below the amp, so I can easily get to it’s rear.

https://www.audiogon.com/systems/9703

whatever is on the bottom can be removed without having to move the heavy amp above. I sized the inside clearance for many/most McIntosh pieces and made the stand hold 100 lbs. for big McIntosh/Other heavy amps.

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I'm here for the audiophool reason 

On top isn't the point, having space and air for cooling is the big deal. If the amp is on top, it has the space and air for ventilation. 

Amps close to the ground,  even my GaN Monoblock's and they weigh nothing compared to my Class A power amps. 

Heat, weight and EMF coupling are your concerns with amps.

Hot air rises, so if in an enclosed space it’s probably best on top. If you have plenty of ventilation it doesn’t matter as much.

Then there’s the weight issue. If an earthquake or tipping over is at all a concern it should be on the bottom.

Lastly, that transformer (assuming a linear power supply) is going to put out a lot of EMF which can couple unexpectedly to other gear if too close to it. Don’t worry, you’ll 100% hear it if it happens. :) It’s not subtle.

In my case I use a 3 shelf Butcher Block Acoustics rack and have my amps on the middle, plenty stable, lots of ventilation.

If your amp is heavy and your rack is tall it really should go close to the ground.