Stumbling around to learn about freqency cutoff/response/etc

[like Yeah!]

ok, so i've built a stumble and decided i don't completely like the eq voicing, but i do like the idea of it being essentially an effects loop in a pedal.
it is too warm, not enough treble definition for me.
the low cutoff seems fine, it's just too warm overall in the upper frequencies.

i want to learn how to swap parts the right way instead of guessing and throwing parts around.. i don't know where to start in this circuit for doing any of this, but i've read enough to know i have to calculate the resistor/capacitor values i'd be changing with a formula to get where i want to go.. so i figured i'd start with a basic circuit like this, and ask. i found some calculators at a site called muzique but i don't know how to make use of that properly so now i'm confused..

1) what parts of that circuit would i want to look at to get a higher/crisper treble cutoff frequency? i'm not sure if i'm stating this properly.. but i'm trying to stay away from le buzzwords as much as i can ha
2) if i were to throw an opa2134 in that circuit instead of the lm833 for reasons, what other parts should i want to look at to keep the opa2134 happy?
3) if i'm asking dumb questions, what should i go read before coming back?

schematic is here. https://docs.pedalpcb.com/project/Stumble-PedalPCB.pdf

thank you

 

[Aentons]

I'm not familiar with this one. Have you tried each part of the circuit separately? From the Input to the Send, and then Receive to the Output. Do they both sound warm, or just one side?

 

[like Yeah!]

I'm not familiar with this one. Have you tried each part of the circuit separately? From the Input to the Send, and then Receive to the Output. Do they both sound warm, or just one side?

good question, so i went and tested that... both sides sound equally 'rounded'..

for more context, while i was testing it again i noticed that it's a subtle difference if you are only playing into it clean.
when you put dirt into it though, it is very noticable.
so for example, it sounds okay out on a pedalboard, but if you stick it in an amp fx loop (or after distortion)... it actually sounds poop because the high frequencies are all shelved off in this weird rounded 'i'mma, a warm circuit' way.

 

[Aentons]

Ok, both sections are similar to an MXR MicroAmp but with different value components and the gain is not variable.

This is a good place to start to understand what the circuit is doing. You don't have to do all the math.

MXR MicroAmp Analysis · ElectroSmash Archive

 

[like Yeah!]

i guess the side with the capacitor (c6 on the stumble) is the side that is controlling the low pass?
both circuits use the same value for the capacitor that doc says is part of the low pass, but use different resistances..
on the microamp that's c2 and the resistor next to it , r4, is 56k..
the resistor next to c6 like that in the stumble is r10, and that's 100k

so that's the reason the stumble sounds duller than the micro amp when it's pushed on?
i should change the 100k resistor at r10 to 56k like the microamp has to get where i want to go? am i in the right direction?

edit- i just looked at the schematic for the transcendence boost again, because i just built one and love how that sounds... it does not appear to have a low pass filter capacitor at all in the feedback loops. does that mean i can simply just remove c6 in the stumble to get the same effect? pic related.