update

1 files changed, 22 insertions, 10 deletions

diff --git a/volume_pot/volume.pl b/volume_pot/volume.pl
index ad1e41c..fff39fb 100755
--- a/volume_pot/volume.pl
+++ b/volume_pot/volume.pl
@@ -3,6 +3,8 @@
 use Math::Complex;
 use Math::Trig;
 
+# proportion of total resistance for a log taper pot
+
 sub logpot($) {
     my $x = shift;
 
@@ -16,6 +18,7 @@ sub logpot($) {
     return $a * ( $b**$x ) - $a;
 }
 
+# proportion of resistance between two points on a log pot
 sub logprop($$$) {
     my ( $v, $t1, $t2 ) = @_;
 
@@ -26,20 +29,32 @@ sub logprop($$$) {
     return ( $v - $t1 ) / ( $t2 - $t1 );
 }
 
+# compute impedance of two elements in parallel
 sub par($$) {
     my ( $a, $b ) = @_;
 
     return 1. / ( ( 1. / $a ) + ( 1. / $b ) );
 }
 
+# impedance of capacitor in nF at frequency f
+sub cap($$) {
+    my ( $c, $f ) = @_;
+
+    my $z = $c * 1.e-9 * 2 * pi * $f;
+
+    $z = -i / $z;
+
+    return $z;
+}
+
 @fns  = ();
 @frqs = ();
 
-# calc gain for taps at te,td frequeny f and knob position k (0-10)
-
+# calc gain at frequeny f and knob position k (0-10)
 sub calc_gain($$) {
     my ( $f, $k ) = @_;
 
+    # position of taps on pot.
     my $te = 0.4;    # terminal e
     my $td = 0.6;    # terminal d
 
@@ -49,11 +64,9 @@ sub calc_gain($$) {
     #terminal b is output
     #terminal a is ground
 
-    my $cnf = -i * ( 1. / ( 0.000000001 * 2 * pi * $f ) );
-
     # loads on terminals d and e
-    my $ld = 18000. + ( ( 1. / 47. ) * $cnf );     #18k+47nF
-    my $le = 4700. +  ( ( 1. / 250. ) * $cnf );    #4.7k+250nF
+    my $ld = 18000. + cap( 47., $f );    #18k+47nF
+    my $le = 4700. + cap( 250., $f );    #4.7k+250nF
 
     #compute resistances of track
     my $rae = $rac * logpot($te);
@@ -78,10 +91,9 @@ sub calc_gain($$) {
     my $etot = $erac;
 
     # input filter
-    $etot += 150000.;                              # 150k
-    $etot += ( ( 1. / 15. ) * $cnf );              # 15nF
-                                                   #balance control
-    $etot += par( 1100., ( 1. / 120. ) * $cnf );   # 1.1k in parallel with 120nF
+    $etot += 150000. + cap( 15., $f );    # 150k +15nF
+                                          #balance control
+    $etot += par( 1100., cap( 120., $f ) );
 
     print "Effective total impedance $erae + $ered + $erdc = $erac\n";