[HAM] Overdrive

[wtimm6801 at aol.com]

 Hello, I've read the articles saying how to add gain to the preamp AO28 swell capacitor for overdrive.  (http://www.dairiki.org/HammondWiki/HowtoAdjustThePreampDriveLevel)  It seems by this method that you have to have the expression pedal floored, the leslie volume knob to 10, and the organ loud as hell to get the growl.  My question is, how do players like Jimmy Smith or Gregg Rolie get that great overdrive sound from, say, playing 868000000 on the lower manual and a half leaned expression pedal at low volumes?  Exactly what amp is overdriving, the Hammond or the Leslie's... or both?
Thanks,
Dylan
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