* =============================================================================
* Midrange channel — Linkwitz-Riley 4th-order bandpass (Sallen-Key)
* Signal chain: HPF(300 Hz) → HPF(300 Hz) → LPF(3000 Hz) → LPF(3000 Hz)
* Op-amps: OPA2134 macromodel (FET-input, unity-gain stable)
* Supply: ±15 V
*
* Download OPA2134 SPICE model from TI if desired:
*   https://www.ti.com/product/OPA2134 → Design & development → Simulation
* VERIFY pinout / supply limits against datasheet before PCB order.
* =============================================================================

.param pi=3.141592653589793
.param f_lo=300 f_hi=3000

* ----- E24-snapped values from calculator.py (ratios kept exact where noted) --
* HP 300 Hz: C=6.8n, R1=56k, R2=112k (=2·R1 exact for Butterworth Q)
* LP 3 kHz:  C1=68n, C2=136n (=2·C1), R=560
.param Chp=6.8n Rhp1=56k Rhp2=112k
.param Clp1=68n Clp2=136n Rlp=560

* Ideal op-amp macromodel (OPA2134-class): high Zin, ~8 MHz GBW, rail clamps
.subckt OPA2134X INP INM OUT VCC VEE
Gerr 0 NERR INP INM 0.01          ; gm → high Aol with Rp
Rp NERR 0 10Meg
Cp NERR 0 1.989e-12               ; dominant pole ~8 Hz → GBW ~8 MHz
Ebuf NBUF 0 NERR 0 1
Rout NBUF OUT 50
D1 OUT VCC DCLAMP
D2 VEE OUT DCLAMP
.model DCLAMP D(Is=1e-15 N=0.01)
.ends OPA2134X

* ----- Source -----
Vin IN 0 DC 0 AC 1

* ----- Stage 1: High-pass Sallen-Key @ 300 Hz --------------------------------
* WHY HPF first: removes woofer-band energy before mid amp; two stages → LR4
C1a IN N1a {Chp}                  ; series C1
C2a N1a N2a {Chp}                 ; series C2
R1a N2a 0 {Rhp1}                  ; R1 to GND
R2a N1a OUT1 {Rhp2}               ; R2 from mid-node to op-amp output
X1 N2a OUT1 OUT1 VCC VEE OPA2134X ; unity-gain follower (INM tied to OUT)

* ----- Stage 2: High-pass Sallen-Key @ 300 Hz (identical → LR4 HP) ------------
C1b OUT1 N1b {Chp}
C2b N1b N2b {Chp}
R1b N2b 0 {Rhp1}
R2b N1b OUT2 {Rhp2}
X2 N2b OUT2 OUT2 VCC VEE OPA2134X

* ----- Stage 3: Low-pass Sallen-Key @ 3000 Hz ---------------------------------
* WHY: truncates mid before tweeter band; two stages → LR4 LP
R1c OUT2 N1c {Rlp}
R2c N1c N2c {Rlp}
C1c N2c 0 {Clp1}                  ; C1 to GND
C2c N1c OUT3 {Clp2}               ; C2 feedback to output (C2=2·C1)
X3 N2c OUT3 OUT3 VCC VEE OPA2134X

* ----- Stage 4: Low-pass Sallen-Key @ 3000 Hz (identical → LR4 LP) ------------
R1d OUT3 N1d {Rlp}
R2d N1d N2d {Rlp}
C1d N2d 0 {Clp1}
C2d N1d MID_OUT {Clp2}
X4 N2d MID_OUT MID_OUT VCC VEE OPA2134X

Rload MID_OUT 0 100k              ; light load into power-amp Rin

* ----- Supplies -----
VCC VCC 0 15
VEE VEE 0 -15
CdecP VCC 0 100n
CdecN VEE 0 100n

* AC: magnitude & phase of midrange bandpass, 10 Hz – 20 kHz
.ac dec 100 10 20k
.print ac Mag(V(MID_OUT)) Phase(V(MID_OUT)) Mag(V(OUT2)) Mag(V(OUT1))

* Expected: flat ~0 dB from ~300 Hz to ~3 kHz; −6 dB at each fc (LR property);
*           −24 dB/oct outside the passband.
.end