Since there is no DC protection in the Job, slight DC leakage from a tubed preamp could go through and damage components in the speaker. At least this is how I understood it from Srajan at 6moons. Regarding preamps with the Job, I have experience with three, all passives. Also, those three preamps were of three different types: Transformer (TVC), Autoformer (AVC), and Light Dependent Resistor (LDR). The TVC was my friend's with transformers from Audio Consulting. The AVC is a Bent TAP-X, and the LDR is the Lightspeed Attenuator (a giant killer from George Stancheff). Although my time with the TVC was brief, it had an OVERALL wonderful sound. Somewhat similar to my LDR. The AVC is, I THINK......SLIGHTLY........EVER SO SLIGHTLY......a touch brighter than the other two. I only had it in the system for two days and I haven't had much time to listen because of a busy work schedule. All three preamps sound amazingly transparent, holographic, detailed, deep and wide soundstage etc,etc. I could HAPPILY live with any of the three. I have to make a decision on either the AVC or LDR but thankfully I'm in no rush whatsoever. I get to live with the AVC and LDR for a while so life is good! The AVC has more "oomph" at lower volume levels than the LDR (which is what I thought would happen), but oh that LDR....there is something so natural and correct about the LDR "sound" that I absolutely love. Forget "good for the money", the LDR may be the best of the best........in the right system of course.