Superphon Rev Preamp. Ridiculously good for the $75 I spent on it used in the early 90's. The Chinese tube mono amps ASL was selling in the late 90's were way better sounding than there asking price. Lowther speakers with the right amps are incredibly good for the the money. You will need a sub though... Just bought a pair of Valvet E1r mono blocks that absolutely sing with the Lowthers.