As many of you know, the GK bass amps all have a boost control. I've usually left mine off for the most part. preamp set between 10-12 o'clock and master on full. I was recently told that running the amp with the boost control turned up will add a certain amount of growl to your tone. So ,I tried it, and I noticed that it did give the tone a little more agressive character. I emailed GK for a technical explanation, and here's what they said: "The Boost control in our amps was designed to give you more even-order harmonics which is what a tube does when driven hard. We use JFET transistors which, when biased correctly, can give you the same even-order harmonics that a tube produces without the bulk and hassle of tubes. So your friend was correct, stating that it gives you more of a tube-style growl along with more tone and volume since it is an extra stage of gain." What are your experiences and preferences with regard to this boost control?