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KZ Volume

VOLUME LEVEL BOOST AND BASS RESPONSE MAXIMISATION FOR THE MAIN ORGAN SIGNALS IN THE PREAMPLIFIER / PERCUSSION AMPLIFIER MODULE.

Remove the R236 120k grounding resistor and short out the R229 68k resistor in order to get a fatter and louder sounding main organ signal. Removing the R236 also increases the volume level of the percussion effect.

WHAT TO DO:

  • Remove the R236 grounding resistor and short out the R229
  • Wire up a 0.1uF capacitor in parallel with the C214 capacitor in order to allow the lowest bass frequencies to fully pass through to the V1B stage of the V1 12AX7 without being attenuated by the R230 resistor and the R232 grounding resistor.

 

ELIMINATE THE UNWANTED REDUCTION IN THE VOLUME LEVELS OF THE MAIN ORGAN SIGNAL WHEN THE PERCUSSION SOFT SWITCH IS SET TO THE "SOFT" SETTING:

Shorting out the R226 resistor in order to increase the volume level of the percussion signal produces the unwanted side effect that the volume level of the main organ signal also becomes reduced when the "Percussion Soft" switch is set to the "Soft" setting because when the switch is set to the "Soft" setting, the R224 150k resistor is connected to the ground thus  lowering the volume level of the percussion effect, and now that the R226 has been shorted out, the R224 also directly affects the main organ signal.

The green wire that is connected to the end of the R224 goes to the RCA socket that has the cable with the red RCA plug plugged into it, and this cable with the red RCA plug  goes to the "Percussion Soft" switch.

I have unsoldered the end of the green wire from the R224, and I then wired up a 15k resistor to the end of the green wire and I then covered this join with heatshrink tube and I then repositioned the end of this 15k resistor to the junction of the collector of the Q201 transistor, the R213 15k resistor and the C209 0.1uF capacitor.

Although I wired up a 15k resistor, you can wire up a resistor value such as a 10k or 15k or 22k or 33k etc resistor depending on the actual desired level of volume level reduction of the percussion signal when the Percussion Soft switch is set to the "Soft" setting.

WHAT TO DO:

  • Unsolder the end of the green wire from the R224 resistor
  • Wire up a 15k resistor to the end of the green wire and then cover this join with heat shrink tube and then reposition the end of this 15k resistor to the junction of the collector of the Q201 transistor, the R213 resistor and the C209 capacitor.
  • Although I have wired up a 15k resistor, you can wire up a resistor value such as a 10k or 15k or 22k or 33k etc resistor depending on the actual desired level of volume level reduction of the percussion signal that you want when the Percussion Soft switch is set to the "Soft" setting.

 

VOLUME SOFT SWITCH MODIFICATION

I have wired up a 10k resistor in parallel with the R407 39k resistor  on the Volume Soft switch in order to increase the mellowing effect of the C401 0.022uF capacitor on the sound when the Volume Soft switch is activated.

This results in a noticeably darker mellower sound as well lowering the overall volume level of the organ.

You can experiment with different resistor values to get the particular desired volume level reduction and mellowing effect.

WHAT TO DO:

  • Wire up a 10k or a 22k resistor in parallel with the R407 resistor on the Volume Soft switch in order to increase the mellowing effect of the C401 capacitor on the sound when the Volume Soft switch is activated.
  • This results in a noticeably darker mellower sound as well lowering the overall volume level of the organ.
  • You can experiment with different resistor values and with different  capacitor values to get the particular desired volume level reduction and the desired  mellowing effect that you want.

 

POWER AMPLIFIER BASS RESPONSE MAXIMIZATION AND GAIN LEVEL BOOST MODIFICATIONS:

Wire up 0.1uF 630V rated capacitors in parallel with the C302, and the C309 0.02uF capacitors and the C311 and the C312 0.047uF capacitors in order to allow the lowest bass frequencies to fully pass through without becoming attenuated by the subsequent grounding resistors in the circuitry.

Turn up the Gain Adjustment potentiometer on the power amplifier to produce the  maximum gain levels.

If you want to increase the gain levels of the power amplifier to allow you to get a Deep Purple Mark II Jon Lord C3 organ through the Marshall amplifier level of heavy distortion then you can disconnect the R337       3.9k feedback resistor which sends the speaker output feedback signal coming from the R336 10k Gain Adjustment potentiometer to the cathode B of the V8 12AX7 phase splitter valve.

I have wired up an SPDT switch in series with the R337 in the power amplifier of my 1963 L102  and I then drilled a hole and then mounted this switch on to a convenient place on top of the power amplifier chassis so that I can switch the R337 in or out of circuit to produce the normal gain levels or the gain boost to the power amplifier.

Please note that when the power amplifier gain levels are boosted by switching off the R337, then when the expression pedal is set to the loud volume levels there will then be some noticeable hum and hiss noise because of the higher signal levels coming from the Percussion amplifier and the Vibrato amplifier, and that the reverb springs might feedback and cause a howling noise because they are so close to the speakers.

WHAT TO DO:

  • Wire up 0.1uF 630V rated capacitors in parallel with the C302, and the C309 capacitors  and the C311 and the C312 capacitors.
  • Turn up the Gain Adjustment potentiometer on the power amplifier to produce the stock maximum gain levels.

Increase the gain levels of the power amplifier to allow you to get a Deep Purple Mark II Jon Lord C3 organ through the Marshall amplifier level of heavy distortion by wiring up a SPDT switch in series with the R337     3.9k feedback resistor so that the R337 can be switched in or out of circuit.

The gain levels of the power amplifier are boosted when the R337 is switched out of circuit.