Guitar preamp distortion/overdrive from single side of 12AX7

[Alva Goldbook]

Hello, everyone!

I have a guitar amp project that I am wanting to incorporate a clean and overdrive channel using a single 12AX7 for the preamp of both channels. I for the clean, I referenced the Silvertone 1482 schematic that uses one side of a 12AX7 that produces a very nice sounding, clean channel that doesn't not break up with a wide range of guitar types. The other side of the 12AX7 I want to be pushed into overdrive at lower volume. I have attached a section of a amp kit schematic that I have built with what they called a "Turbo" mode that accomplishes this, but I don't necessarily understand how adding a cap that bypasses the tone stack creates this effect. Without adding another tube to implement a cold clipper or an additional drive stage, are there any other (better?) methods to create obviously intentional distortion?

Thanks!

Paul

As a general rule of thumb, to get a decent lead sound using 12ax7s, you'd need 3 gain stages plus a phase inverter if it's push pull. Yes, there's ways, to really get 2 gain stages to get some hair going, but 3 is the practical threshold for a good lead sound. For a good clean sound, 2.

I would note, however, that adding more gain stages to a clean sound for cleanly biased 12ax7s sounds lovely. Many blackface era Fenders had a 2 gain stage plus PI thing going, but if they had added a 3rd, they would have sounded much better.

You can add a single triode to get a clean and lead sound. I mean the JCM 800 2203 did that. But if the clean and lead sounds only have a single gain stage, I'm afraid it's just not going to get there.