FatMan Hard Sync Modification          by Scott R. Gravenhorst
                                       chordman@ix.netcom.com

Please email comments regarding this mod to:
chordman@ix.netcom.com

As you can see from the .BMP, this is pretty simple.

The switch allows either VCO to sync to the other.

How it works:

The .001 uF capacitor acts as a differentiator, ie it creates a 
spike on each transition of the square pulse output on pin 3 of 
the VCO's 555 timer IC.  The positive spikes are selected by the 
diode and allowed to influence the 'trip' voltage of the other 
VCO's 555 timer.  This kick in the pants causes the sync'd VCO to 
terminate it's current cycle and discharges it's capacitor.  Then 
it begins a new cycle.  

In combination with an LFO modulating the frequency of either 
VCO, or just by itself, oscillator sync can produce very 
interesting results.