Abstract: We apply a feedback cooling technique to simultaneously cool the three electromechanical normal
modes of the ton-scale resonant-bar gravitational wave detector AURIGA. The measuring system is based
on a dc superconducting quantum interference device (SQUID) amplifier, and the feedback cooling is
applied electronically to the input circuit of the SQUID. Starting from a bath temperature of 4.2 K, we
achieve a minimum temperature of 0.17 mK for the coolest normal mode. The same technique,
implemented in a dedicated experiment at subkelvin bath temperature and with a quantum limited
SQUID, could allow to approach the quantum ground state of a kilogram-scale mechanical resonator.