Depends on the distance between your components. I wouldn't place the power amp on the one stand with small signal components because there is a possibility of induction of parasite currents if the power transformers aren't shielded well. It may cause hum. Simply saying power amp should stay away from other components and certainly have much more room for heat dissipation. If your stand has large enough space(so that preamp is above at least by 4" from power amp)it maybe OK.
7 responses Add your response