my Fatman got its brain confused
Posted: Sun Mar 13, 2011 7:23 pm
So I was trying to add the cmos subharmonic generator mod to my fatman and it wasnt working properly, kind of in and out so i disconnected it and noticed my midi signals seem to be a bit confused now. The mod was tied in at ic14 voltage regulator for gnd and -12 v, both 555s pin 3, and ic17 lm13700s pin3 vcf in. What is odd is that now the midi seems to be a little scrambled with the mod removed. the first octave (c0 - 1) works fine but as you move up the scale and get to c#1 it plays a note equal in pitch to approx. a0. D1 is about a b0 in pitch and so on until you get to c#2 which jumps back to the pitch of c#2. Its as if all of octave 1 is transposed down 4 notes and only does this in octave 1. I dont think this is a 555 issue because both vcos do the same. Vcf seems to work fine. Could this be a voltage regulator issue? Its still reading -12 and -5 at its output/input. also just in case the 555s are swapped with cmos ones and i added and lee diode mod. also noticed that when i just barely touch the trimpot at r21 it jumps in pitch and rotating it in either direction doesnt produce a smooth pitch change like the other trimpots. theres nothing shorting physically on the trimpot but its behaving rather erratically. ill try to replace it but i think that its probably a result of a larger problem.