SPICE Models

These germanium BJT SPICE models are based on the Gummel-Poon parameters from Table 1 in "Comparison of Germanium Bipolar Junction Transistor Models for Real-Time Circuit Simulation”, Proceedings of the 20th International Conference on Digital Audio Effects, Edinburgh, Scotland, Sept. 2017. The parameters were extracted from vintage OC44 and AC128 components.

* B. Holmes, M. Holters, M. van Walstijn. “Comparison of Germanium Bipolar Junction Transistor Models for Real-Time Circuit Simulation”, Proceedings of the 20th International Conference on Digital Audio Effects, Edinburgh, Scotland, Sept. 2017

.MODEL OC44 PNP(IS=1.423u BF=307.0 BR=20.27 NF=1.022 NR=1.025 VT=25.5m VAF=8.167 VAR=14.84 IKF=43.82m IKR=611.7m ISE=30.54n ISC=213.5n NE=1.316 NC=1.258 RB=32.83 RE=968.7m RC=989.9u CEB=410p CCB=10p)

.MODEL AC128 PNP(IS=20.66u BF=229.6 BR=14.66 NF=1.133 NR=1.140 VT=25.5m VAF=19.68 VAR=88.28 IKF=463.0m IKR=241.5m ISE=2.190u ISC=7.546u NE=1.796 NC=1.364 RB=1.885 RE=306.4m RC=1.727u CCB=100p)
      

The models have been tested in ngspice, successfully reproducing results from the paper (see holmes2017 directory in repository).

OC44 Test Results

Common-emitter characteristics plot (compare to figure 6 in paper):

Rangemaster circuit simulation response to 500Hz sinusoidal input (compare to figure 10 in paper):

Rangemaster circuit simulation audio samples (compare to https://bholmesqub.github.io/DAFx17/):

• chord (rangemaster)
  
• chord (dry)
  

AC128 Test Results

Common-emitter characteristics plot (compare to figure 7 in paper):

Fuzz Face circuit simulation response to 500Hz sinusoidal input (compare to figure 11 in paper):

Fuzz Face circuit simulation audio samples (compare to https://bholmesqub.github.io/DAFx17/):

• chord (fuzzface at max fuzz)
  
• chord (dry)
  

Running the Tests

The tests run on MacOS with

• ngspice http://ngspice.sourceforge.net
• python3 https://www.python.org
• spice-audio-tools (with my fixes) https://github.com/grwhitehead/spice-audio-tools

OC44 Characteristics

% cd holmes2017/oc44
% ./plot.sh oc44
      

OC44 Rangemaster Circuit

% cd holmes2017/oc44-rangemaster
% ./plot.sh rangemaster
% ./chord.sh rangemaster
      

AC128 Characteristics

% cd holmes2017/ac128
% ./plot.sh ac128
      

AC128 Fuzz Face Circuit

% cd holmes2017/ac128-fuzzface
% ./plot.sh fuzzface
% ./chord.sh fuzzface