Q on Rat's filter in FB loop

[strungout]

Oy.

I just breadboarded it this afternoon and I like it alot but....  :roll:  I was thinking it could use a bit less mud. I tried different cap values at input, output and somewhere in between, and that's where I get around to messing with the wierd "two-handed arm" in the feedback loop and wondering what kind of filter it is actually. I did search the forums when I was looking for mods, but nothing. Are they just two lowpass in parallel? How would I calculate what freqs they're affecting? Any info on this would be cool. Otherwise, it's BMP tone ctrl time  

I had seen different types of "arms", like a gyrator in the DOD death metal (what it seemed like anyway).

Ciao.

[cd]

Actually they're two high pass filters (cut lows).  You can use the standard equation to find the cutoff frequency:

F=1/2*pi*R*C, where R = resistor in M ohms (so 4.7k would be .0047) and C = capacitor in uf.

[Transmogrifox]

The overall effect is high-pass.  Those two series RC networks pass more current at higher frequencies.

Each one sets a corner frequency on it's own and it's simply calculated as :

1/(2*pi*R*C)

ignoring the other.   Just pretend the '-' terminal is an ideal voltage source so that the effect of one RC network does not effect the other--so calculate each one as if there was only one of them like a TS-9 has or something.

like any simple first order low-pass filter (it looks low pass from the '-' terminal of the op amp, but since the op amp adjusts to keep the '-' the same voltage as the '+' terminal, it must increase the output voltage at higher frequencies where it rolls off to compensate)

The pass-band gain is the gain that one would calculate if those capacitors were shorted...R1/R2 form.

The gain for really low frequencies is 1, increasing at a rate of 20 dB per decade up to the maximum pass band gain.

[strungout]

Well, I got rid of the muddiness. But I still want to get this.

So, here's what I understood: what looks like a LP filter at the inverting input side of the fb loop actually as the reverse effect, and from the center freq. get progressively more gain. So, in the rat, that would make the gain increase from 60Hz and some more from 1500Hz, giving more proeminence to the freqs above 1500Hz?
If I put in a HP configuration, it would act as a LP and I would get the opposite effect?

Did I understand that correctly?