Tone stack in ODS models

[greiswig]

I'm a little confused about the ODS 100 Clean in particular. The wiki states that it is "...based on HRM circuit, Clean channel." Ordinarily, you can check that by swapping the tone stack from "Default" to whatever it's supposed to be, and nothing should change when, in this case, you swap tone stacks from Default to Rumble HRM." But it does change, and pretty drastically.

As near as I can tell, what is actually on the ODS 100 Clean is the Skyliner tone stack, with a mid frequency of 400Hz and set to the "Mid" location. But the Skyliner stack has a center frequency closer to 650Hz, doesn't it? It sounds good, but if the aim is authenticity, it feels like either the model is wrong or the wiki is. And if it IS modeled on the Skyliner circuit and not the HRM, it seems like the frequency and location are wrong. Both the HRM and the Skyliner tone stacks were after the first triode stage, which as I understand it would be in the "Pre" location. Again, according to the wiki, "“MID” places it between the last two triode stages," so that seems wrong.

Another question I have is about the behavior of those three controls together: tone stack, frequency, and location. It feels like they should "travel together" with the user being able to override as needed. But they don't. That seems like an odd behavior given how critical those two factors are in how the tone stack affects the amp.

 

[FractalAudio]

The default tone stack for this model is a Skyliner with location set to "Mid". This matches the reference amp. The frequency is arbitrary, it's just a reference value and if you don't change it the tone stack is accurate. Regardless, the notch frequency is approx. 422 Hz so the value of 400 Hz is appropriate.

No idea what "travel together" means.

 

[greiswig]

The default tone stack for this model is a Skyliner with location set to "Mid". This matches the reference amp. The frequency is arbitrary, it's just a reference value and if you don't change it the tone stack is accurate. Regardless, the notch frequency is approx. 422 Hz so the value of 400 Hz is appropriate.

No idea what "travel together" means.

Interesting about your reference amp. So it actually has the tone stack after V1's second triode stage?

What I mean by "travel together is this: I think of all of these three components of the tone stack...

• Tonestack Type - what the pot values and tapers are, capacitors, etc.
• Tonestack Frequency - determined by above, interacting with the surrounding circuit
• Tonestack Location - where these components sit in the overall circuit

...I think of all of these things as a Gestalt, and in the real world the latter two are determined by the Tonestack Type. For example, you don't see an AC-30 with a tone stack that has a center frequency of 400Hz in the "Pre" position. When you select that amp model, what it comes up with is the default (which really is, I believe, the Class A Brilliant tone stack), 700Hz and "Post." All well and good up to this point.

The problem is that now, if I want to change that tone stack to something else, I can change the Tonestack Type, but the other two parameters remain as though I hadn't changed the tone stack at all. I'm sure that there may be combinations that are topologically impossible in terms of the position of the tone stack, but at the very least I'd expect that the Tonestack Frequency would be determined by the Tonestack Type, and the Tonestack Location would also, if possible.

TL;DR - That's what I mean by "travel together." That the Type should determine the other two parameters when selecting a different Tonestack Type.