After a backorder of over 3 weeks my TH500 was delivered today. The first thing that struck me was how much lighter it was compared to my Genz Streamliner 900. I'm no stranger to the class "d" heads and this is the lightest I have had. With all of the controls at noon, excluding the gain, and running through an Aguilar DB112 the tone was, to my ears, aggressive and modern with a vintage feel. It is totally different than my STL-900. I went through all of my basses with it making slight eq adjustments. I played my 44-02's and 55-01 with the onboard eq's flat and was impressed how warm and crispy the tone was and how aggressive and responsive the head was. With my jazz and p bass, the aggression was still there but the tone was responsive to attack and not boomy at all. This is a totally different beast than the STL-900, but I really love them both. In the past I had a Genz Shuttlemax 9.2 which I primarily used for more modern rock gigs. Ultimately, the Streamliner won over the 9.2 because I only used the FET channel. The TH500 is the sound that I wanted from the 9.2. The characteristics between the TH500 and the STL-900 are like comparing a Maserati to an Aston-Martin. Both sound so good but are refined in vastly different ways. The STL-900 is much more tubey goodness and vintage warmth. The TH500 is more aggressive and vintage warmth. Rolling off the highs on the active basses and rolling off the tone in the passive basses yields tubey warmth. If you can have both, do it.