How this mid scoop works

This is the second passive mid scoop in the family, built a different way from its sibling. R1 and R2 sit in series between input and output with C1 bypassing the pair, and the pot’s wiper is grounded, which splits its track into two independent legs to ground: the input side reaches ground through C2 plus one section of track (R_a), the output side through C3 plus the rest (R_b). Nothing connects between R1 and R2, so electrically only their sum matters; they stay two parts in the build list because that is how you would build it.

At low frequencies both legs are open (the caps block) and the series pair just passes the signal: unity. At high frequencies C1 bypasses the pair entirely, corner at 1/(2π·(R1+R2)·C1), about 2.4 kHz stock. In between, the legs conduct and pull the signal down: the scoop. Turning the knob slides the grounded tap along the track, trading leg resistance between the two sides. Toward 100% the output leg firms up and the scoop deepens; with a buffer driving it the stock network runs about 7.2 dB deep at 404 Hz at noon. At the very ends of the travel one leg’s resistance hits zero and the network stops being a scoop: that cap then shunts a node directly and the response collapses into a heavy treble shelf (at full depth the highs land on the C1-to-C3 capacitive divider, about −34 dB with the stock caps). The usable scoop lives in the middle of the rotation, which is exactly how this kind of control feels on a real pedal.

R4 is the part that makes the input side of this network real. This page assumes a buffered, low-impedance signal feeding R4; the resistor then gives the network a defined source to work against. Without it, C2 and the input half of the pot cannot do anything: slide R4 down to its 0 Ω jumper (buffer straight in) and watch C2 stop mattering entirely, because a stiff source pins the input node. At the stock 10k the input leg pulls its weight, the noon scoop runs about 9.4 dB deep at 419 Hz instead of the 7.2 dB you get buffer-direct, and the bottom of the knob’s travel shades into a treble cut because C2 then shunts R4 directly. Passive tone networks always care what drives them; R4 pins that answer down so the control behaves the same on every rig.

Everything assumes a buffered low-impedance source into R4 and a high-impedance stage after the output, a buffer or an op-amp input; break either assumption and the numbers shift. All eight parts are adjustable and the four resistors run to true 0 Ω jumpers. The dashed curve is the nearest-E12 build with the nearest standard pot value.