After reading that book, I feel a lot less bright. So much so that I'll have to have his next book read to me.
In fairness, it does seem like the guy is looking for a zebra to solve a problem that a horse could easily handle.
How exactly do Treble and Presence controls fall short in “taming brightness,“ exactly? The guy hasn’t even mentioned what specific Marshall circuit he’s talking about.
If it’s a modern master volume Marshall, Treble and Presence should work fine. If you absolutely have to spend money, put an EQ in the loop or something. You’re going to get infinitely more flexibility out of that than the extremely subtle changes you may or may not perceive with preamp tubes, not to mention their modern manufacturing consistency issues. Any given two of the same type could be brighter or darker, fatter or thinner, whatever. You never know with tubes these days. seems like amp or external EQ controls would be a lot more reliable and predictable to me at least.