I actually have a couple of preamps now, and both of them work great with the Red Dragon amp. I use a Dodd Adj. Gain battery powered preamp, and also a Decware CSP2+ preamp. The latter let's me really tailor the sound by swapping and mixing tubes. Both preamps have been modded with Jupiter copper foil caps. Both preamps have amazing sonic qualities, much, much beyond their price points, and synergize very well with the S500.