As a quick distraction from the everyday I decided to jump down the guitar amp rabbit hole again. I've been looking into "intentional" distortion, and something doesn't make sense to me. In higher end amplifiers, distortion is usually created by cascading multiple gain stages, cumulatively driving the last tube of the preamp, and then into the power section. Couldn't that same effect be created by using an op amp circuit with sufficient gain pumped into that last tube stage? For that matter, couldn't some of that distortion also be supplanted by diodes in the same circuit in order to account for the lack of it in prior gain stages? Or would that not matter since you would be driving that tube with so much gain anyway?... Or is this another case of "you missed this..."?
Not necessarily, because the opamp can clip (which has high energy in all the overtones) - you'd have to ensure sufficient headroom so only the tube stage brings soft non-linearity to the signal. And yes people use diodes all the time for distortion, half the guitar effects made probably did this (until digital took over)?
I was thinking of using something a little sexier like an OPA891 as opposed to the typical TL072 you would find in most pedals. That should have more than sufficient headroom in terms of just the signal going into the tube. I figured, since those initial stages being 12ax7 are each somewhere shy of 100mu, a single higher quality op amp should be more than sufficient to fill that role.
Right, I just wasn't sure if I needed anymore going into the second stage (being the preamp tube). The distortion would typically build slowly from those concurrent stages, so I was a little unsure if there would be any consequence from not having multiple stages like that.