JDS Labs Subjective3 Tone Control Equalizer

I'm contemplating this kit:

JDS Labs - 3-Band Equalizer DIY Kit - DIY Kits

It appears to be able to support minimal mods:

Electronic Projects: JDS Labs Subjective3, Part 2

I've attached a schematic of the tone control "stack" as utilized by JDS Labs as well as the same schematic from the TI documentation for the OPA227 op amp. My questions are as follows:

1. What type of "tone stack" is this? It appears to be some kind of modified Baxandall?

2. I want to change the bass frequency and, with a conventional Baxandall circuit, this can be accomplished by changing the capacitors associated with the bass control. There appear to be no caps associated with the bass control or I am missing how this configuration operates.

3. Is there a LTspice model for the OPA227?
 

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I think the bass control turnover frequency depends on C1. Obviously if you change it, then you change the midrange control as well.

This is a truly terrible circuit for customizing. There's so many tone control circuits, why not find a better one with a much simpler transfer function?

If you read the blog, you can see that someone tried to modify it and they were very dissatisfied with the results. Why go down that path again?

Another glaringly obvious defect of this circuit is that they put a buffer on the output, instead of the input where it's needed. Plus there is no isolation from cable capacitance etc. It's what I would call an incomplete (or very poorly thought out) circuit.

What did they think this circuit was going to be driven with? Were the "engineers" aware that the input impedance changes radically with tone control setting? Were they aware that you need a resistor on the output for stability? So many facepalms.

http://bitsavers.trailing-edge.com/...aBooks/1980_National_Audio_Radio_Handbook.pdf Look at figure 2-53. That's what you want to build. The equations for the transfer function are right there so you can customize it. You don't have to use their obsolete op amp specified. 5532 or 2134 is better.

If you don't like that circuit, look up Walt Jung's tone controls. They're the best and they're easy to customize and add features to (like variable turnover frequencies). They can be casacaded and they don't affect the other controls.

Finally, Rod Elliott has some interesting tone controls. They're worth a look. But this kit you linked to is truly terrible, half baked, and there's no excuse for offering as product like this.