vivaAnalog-RCA12ax7 Spice Model update // Gain Sims

gain figures are now lining up with my original ’94 Quadra640-Intusoft derived results … as an example, we can compare the AC simulation output of a typical Common-Cathode gain stage produced by using my updated RCA12ax7 Spice model against Randall Aiken‘s run-through of the corresponding “incremental” algebra using idealized terms :

http://www.aikenamps.com/

we find that his math derives a un-bypass’ed cathode (ie., absence of cap-to-ground on the Cathode) AC voltage gain of 30dB, and a cathode-bypassed voltage gain of 35dB for a “typically” biased 12ax7 Common-Cathode gain stage // … of course, good modeling should corroborate such known results, and right on the money mostly …

as with any kind of non-linear network/device transfer modeling this form of AC-response comparison does not validate the large-signal aspects of the model … but it is a first step heading in that direction // … thank-you Randall !

here’s my RCA12ax7 model adapted to TINA-TI’s Spice syntax rules:

.subckt vivaAnalog-RCA12ax7 1 2 3
*************************
eGIogVpc 20 0 value={log(v(1,3))}
rGlogVpc 20 0 1
eG0 10 0 poly(1) 2,3 -3.7694e+00 1.9947e+00 5.9432e-02
eG1 11 0 poly(1) 2,3 -3.2024e-02 -4.1443e-02 -4.8236e-03
eG2 12 0 poly(1) 2,3 1.9127e-02 -1.2189e-02 -1.5526e-03
eG3 13 0 poly(1) 2,3 -1.1354e-02 4.9339e-03 6.1016e-04
rG0 10 0 1
rG1 11 0 1
rG2 12 0 1
rG3 13 0 1
gG 2 3 value={(exp(v(10)+v(20)*(v(11)+v(20)*(v(12)+v(20)*v(13)))))/170}
eP0 110 0 poly(1) 2,3 -9.9158e+0 1.9145e+0 -2.8135e+0 1.8661e+0
+ 1.5643e+0 4.7240e-1 6.4276e-2 3.3101e-3
eP1 111 0 poly(1) 2,3 9.5428e-1 3.2558e-2 -8.3349e-1 -4.8578e-2
+ 2.6213e-1 1.0492e-1 1.8921e-2 1.3632e-3
eP2 112 0 poly(1) 2,3 9.5766e-2 2.5192e-2 2.2391e-1 -1.7040e-1
+ -2.4952e-1 -1.0960e-1 -2.0981e-2 -1.4882e-3
eP3 113 0 poly(1) 2,3 -6.6107e-2 -3.9657e-2 7.5560e-2 3.1025e-2
+ 2.4265e-2 1.7002e-2 4.2512e-3 3.4761e-4
eP4 114 0 poly(1) 2,3 8.4148e-3 4.7989e-3 -1.3258e-2 -1.9288e-3
+ 5.2888e-4 -5.6853e-4 -2.4727e-4 -2.4359e-5
rP0 110 0 1
rP1 111 0 1
rP2 112 0 1
rP3 113 0 1
rP4 114 0 1
gP 1 3 value={(exp(v(110)+v(20)*(v(111)+v(20)*(v(112)+v(20)*(v(113)+v(20)*v(114))))))}
Cgc 2 3 1.8p
Cgp 2 1 1.7p
Cpc 1 3 1.9p
.ends



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