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KZ Expression

EXPRESSION PEDAL VOLUME CONTROL POTENTIOMETER MODIFICATION TO ALLOW A MUCH GREATER RANGE OF VOLUME LEVEL CONTROL BETWEEN THE SOFTEST VOLUME LEVEL SETTINGS AND THE LOUDEST VOLUME LEVEL SETTINGS.

THIS APPLIES ONLY FOR THE EARLY L100 SERIES ORGANS:

When my modified 1963 L102 organ is played at full volume, the above mentioned  modifications that noticeably boost the overall gain levels will allow the stock built in power amplifier to distort to similar levels as that of a Leslie 122/147 etc amplifier when playing a B3/C3 etc organ at full volume thus turning my 1963 L102 organs into a real nasty beast, and if the L100 series organs that are modified this way are connected to a Leslie 147 / 122 etc then the modifications that boosted the gain levels will allow a lot more overdrive to be created by the Leslie 147 / 122 amplifier.

However because of the limited volume level range of the stock expression pedal circuit , the organ will be too loud even when the expression pedal is set at the minimum volume level setting, but after some experimentation I overcame this problem with the following modification.

Please note that the following modification  only applies to the earlier era L100 series organs that had the 250k expression  control potentiometer. I have never experimented with the Light Dependent Resistor (LDR) based  expression pedal volume controls of the later L100 series organs, however I do expect that the organs with the LDR based expression pedals can also be modified to allow for a similar drastically increased range of volume control between the lower settings and the full volume setting but I do not know what are the exact component values to be changed or added to the LDR circuitry.

With the older L100 series organs that have the 250k potentiometer in the expression pedal you can unscrew and pull out up the expression pedal and then rewire the circuit as follows:

Connect a 220pF capacitor in parallel with the existing C501 47pF capacitor that is wired between the input and the output of the circuit. The input side connects to the junction of the outer pin of the R501 250k potentiometer and one end of the C501 47pF capacitor.

Short out the R502 100k resistor that is wired between the middle wiper pin of the R501 250k potentiometer and the junction of the C501 47pF capacitor and the output.

Connect a 470 Ohm resistor in parallel with the R503 4.7k resistor that is wired in series with the other outer pin of the R501 250k potentiometer and the C502 0.047uF grounding capacitor.

Connect a 0.47uF capacitor in parallel with the C502 0.047uF grounding capacitor.

The above modifications to the expression pedal circuitry drastically increases the volume level range between the minimum level setting and the maximum level setting thus allowing you to go from a very quiet level to a very loud and overdriven level, and you still get the bass boost and treble boost frequency compensation effect at the lower volume level settings of the expression pedal.

Even though I have noticeably boosted the gain levels of the main organ signal and the percussion signal with the  modifications mentioned previously, my 1963 L102 organ still sounds clean  when the expression pedal is set to the lower volume level settings but the sound becomes nice and dirty when I set the expression pedal to the louder volume level settings.

If you want the organ tonality to be the same at all of expression pedal settings, you can simplify the wiring of the expression  pedal circuit by removing the C501 47pF capacitor that is wired between the input and the output of the circuit, and you can short out the R502 100k resistor that is wired between the middle wiper pin of the R501 250k potentiometer and the junction of the C501 47pF capacitor and the output and you can short out the C502 0.047uF grounding capacitor, and you can wire up a 470 Ohm resistor in parallel with the R503 4.7k resistor that is wired in series with the other outer pin of the R501 250k potentiometer and the C502 0.047uF grounding capacitor.

If you want the volume level to be quieter when you set the expression pedal to the minimum volume level setting, you can experiment with wiring up a lower value resistor in parallel with the R503 4.7k resistor and if you want the organ sound to be completely silenced when you set the expression pedal to the minimum volume level setting you can then simply short out the R503 4.7k resistor and the C502 0.047uF capacitor.

 

WHAT TO DO:

  • Unscrew and pull out up the expression pedal and then rewire the circuit as follows:
  • Connect a 220pF capacitor in parallel with the existing C501 capacitor.
  • Short out the R502 resistor that is wired between the middle wiper pin of the R501 potentiometer and the junction of the C501 capacitor and the output.
  • Connect a 470 Ohm resistor in parallel with the R503 resistor.
  • Connect a 0.47uF capacitor in parallel with the C502 grounding capacitor.

 

    If you want the organ tonality to be the same at all of expression pedal settings, then do the following:

     

  • Remove the C501 capacitor.
  • Short out the R502 resistor.
  • Short out the C502 grounding capacitor.
  • Wire up a 470 Ohm resistor in parallel with the R503.
  • If you want the volume level to be quieter when you set the expression pedal to the minimum volume level setting, you can experiment with wiring up a lower value resistor in parallel with the R503 resistor.
  • If you want the organ sound to be completely silenced when you set the expression pedal to the minimum volume level setting you can then simply short out the R503 resistor and the C502 capacitor.