I've built a Tweedy Bird drive that is a lot of fun to play. My only problem is that the treble is a little much. The J201's are Fairchilds and biased to around 4.5-5V. I'm looking for ideas where I can cut some treble from the circuit without changing the character too much. Playing with the Tone Stack calculator doesn't seem like there is much flexibility in the treble side (at least beyond what is already in there). Between Q4/Q5 and Q6, it looks like there is some additional filtering where R13, C13, and R15 form a low pass filter (based on my limited electronics knowledge). I think if I lower R15, that should drop the treble across the board. Am I right?