From chordman@ix.netcom.comWed Jun 21 11:18:02 1995 Date: Wed, 21 Jun 1995 09:06:01 -0700 From: "Playing@Blues.Guitar" To: analogue@hyperreal.com Subject: FatMan mods mailing list? Dear Analogue Heaven: I got wind of a possible mailing list regarding 'Analogue Heaven' thru conversation with a member of rec.music.makers.synth. I would like to be both a contributor as well as a recipient. Please find below descriptions of 3 mods which I have completed and that work. If after reading this you are still interested, email me and I will send you the .BMP drawings for mods 2 and 3 as well as a how it works text file. I do not have an etched board, since I breadboard everything. FatMan mod description file Scott R. Gravenhorst chordman@ix.netcom.com Currently the 3 mods I have are described below. I am working on more. Also I was informed that a mailing list at analogue@hyperreal.com is available to us. I intend to mail my stuff there as well. I am not sure what the parameters for membership are, but I will find out. You might want to shoot them an Email as well. 1) This is an easy one. I found that the offset control was too coarse to easily adjust for a desired amount of 'flanging' between the two VCOs. I simply wired a 5K pot in series with the existing 100K offset pot. This creates a coarse/fine system with a 20:1 or 5% range. This does not change the total adjustment range. To use it, you set the fine control to mid range. Then adjust the coarse control (100K) to approximately the pitch desired. Finally, adjust the 'fine' control (5K) to get the exact flange effect you want. Real easy. 2) This one requires adding circuitry to the FatMan, but no trace cutting. This add on is a subharmonic generator. Basically, it is a digital divide by 2 counter driven by VCO2s square output (555 timer, pin 3) to produce exactly one (or two) octave(s) below VCO2s output as a square wave. This square wave is routed through a simple RC lowpass filter to control harmonics and then to a level control. The output of the level control is then mixed with the output of the 1/2 mix control. With these controls you can bring up (from zero) the subharmonic and also control the 'roundness' of it. The result is the ability to create a richer harmonic structure. On of my favorites is to set VCO1 a fifth above VCO2 and add the subharmonic to VCO2. This produces thick, thundering bass. Adds 2 IC chips to the FatMan (on a separate board) 3) This add on requires adding circuitry to the FatMan but again, no trace cutting. This circuit adds a simple LFO to control the pitch of VCO1. It allows a nice flange effect that keeps changing. Controls are level and LFO frequency (down to around .1 Hz, but component values may be changed to provide a different range. Adds 1 IC chip to the FatMan. *WARNING* With all adds and mods, it is wise to monitor the heat dissipated by the 3 voltage regulators. It may be necessary to either add a heat sink (to the -12V) or to move the power supply off board and use a heftier regulator (T-03 package) and larger heat sink. You may alternatively use a fan, but that increases ambient room noise. -- Bela Bartok Rocks!