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PAiA 9308 FatMan General MODs
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PAiA FatMan General Mods
Well, these are just basic must-do mods. I'm keeping these notes and details here, in case i'd ever need to re-do a FatMan again. Will save some time trying to search for locations of the resistors and so on, which is difficult on the PCB after components are soldered in. Save time having to refer back and forth the manual & diagrams etc.
Note: Most of these mods are from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site.
bulletLee Diodes
 Replace R38/R39 with LEDs + add 100uF caps to C28 and C29
bullet555 -> 7555
 Replace 555 IC's with 7555's
bulletVCO Pitch Extend
 Change R35 (1k resistor) to a 680R
On FatMan Rack#1, I added a Switch to bypass R35, but this time I feel I don't wanna spend lots of time tuning this thing - so i just reduced the 1k resistor.
bulletVCO Fine Tune
 Additional 5k Pot in series with the Pitch Offset
bulletNew Hard Sync
(Switch)
 VCO1 (Pin4) reset by VCO2 (Pin3) - I cut the PCB trace at VCO1 Pin4 to add the switch.
bulletVCF BP/LP Select
(Switch)
 Extra wire out of the Filter IC to a switch
bullet Extended VCF Freq
(Switch)
 Switch to short resistor R73
bulletMax Resonance (Switch)
 Switch to short resistor R114

LEE DIODES
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
The Lee Diode modification, named after Scott Lee - to reduce SOFT SYNC.

Directions:
1. Replace R38/R39 with LEDs. (The arrow must point away from pin 1 of the 555 to which it is attached).
2. Add 100uF (same voltage rating) capacitors in parallel with the ones that are already bypassing the 555s, ie C28/C29.
Note: On the actual PCB, the LEDs replacing R38 points to the top, and the LED replacing R39 points to the bottom of the PCB.

555 -> 7555
Replacing the two 555 IC's (IC15 / IC16) with 7555. This reduces soft sync even further, and also improves quality and stability.
NOTE: On my 2nd FatMan, I tried to experiment - i only changed IC15 (VCO1) into a 7555, and left IC16 (VCO2) as the original 555.

VCO Pitch Extend
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
Shorting R35 or reducing it will produce Extended Low End.
R35 is a 1k resistor.
On FatMan#1, I added a switch to short it. The VCO Pitch range is slightly too wide for my taste, so on FatMan#2, I reduced it to 680R.
R35 is located in the centre of the PCB, under the pads, D, A, C.

VCO Fine Tune
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
VCO Fine Pitch / Fine Pitch Offset Mod.
Add a 5k Pot for Fine Tune in series with the Pitch and/or pitch offset control to create a coarse/fine system.

Hard Sync Switch
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
Add Hard Sync syncing VCO2 to VCO1. 
Basically use a switch to switch in VCO2 (IC16 Pin3) to VCO1 (IC15 Pin4).
The way i did this, TRACK CUTTING IS REQUIRED.

VCF BP/LP Switch
from John Sepulveda's Multimode VCF Mod
Add a switch to to switch between normal LP and additional BP Filter.
Directions:
1. Remove positive side of C23 and attach that to the center pole of a SPDT switch
2. Run a wire from the the board where you just removed C23 to one of the other poles on the switch
3. Connect a lead from Pin 8 of IC17 to the last remaining pole on the switch
C23 and IC17 are at the LEFT of the PCB:

VCF Frequency Extend Switch
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
Shorting R73, with an SPST Switch.
R73 is the resistor mounted on the frequency Pot...

VCF Maximum Resonance Switch
from Scott R. Gravenhorst's excellent Synthaholic's Fatman Site
Break the connection between R114 (Resonance Pot) and Wire "J" with an SPST Switch.

 

 

FatMan 1u Rack #1

FatMan 1u Rack #2

FatMan #3  / 2u Rackmount

 

 

 

 

 

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