website design software
KZ Preamp

PREAMPLIFIER / PERCUSSION AMPLIFIER MODULE MODIFICATIONS TO THE V1A STAGE OF THE V1 12AX7 INPUT VALVE:

The following modifications to the V1A stage of the V1 12AX7 only  affect the main organ signal but they do not affect the percussion signal.

 

TREBLE BOOST MODIFICATION TO THE V1A STAGE OF THE V1 12AX7 INPUT VALVE IN THE PREAMPLIFIER / PERCUSSION AMPLIFIER:

Increase the high treble response to be more like that of the M-series organs by adding a 1.8M resistor in series with the C203 39pF feedback capacitor.

If you want a real screaming treble response , you can completely remove the C203 39pF feedback capacitor.

On my  1963 L-102 organ I have installed a single pole / two position (SPDT) "centre off" switch that allows me to switch between three different treble response settings which are as follows:

Position 1) The normal stock setting with the C203 switched in place

Position 2 Middle position "centre off " setting) The C203 is completely switched out of circuit thus resulting in a upper midrange and treble boost for a bright screaming organ tone with much more key click.

Position 3)  A 1.8M  resistor is wired in series with the C203 thus resulting in a brighter high treble response and more key click so that the response is more like that of an M series or M100 series organ.

WHAT TO DO:

  • Install a SPDT "centre off" switch that allows you to switch between three different treble response settings which are as follows:
  • Position 1 ) The normal stock setting with the C203 capacitor switched in place
  • Position 2 Middle position "centre off" setting) The C203 is completely switched out of circuit thus resulting in a upper midrange and treble boost with much more key click.
  • Position 3 ) A 1.8M resistor is wired in series with the C203 thus resulting in a brighter high treble response and more key click so that the response is more like that of an M series or M100 series organ.

 

BASS BOOST MODIFICATION TO THE V1A STAGE OF THE V1 12AX7 INPUT VALVE IN THE PREAMPLIFIER /  PERCUSSION AMPLIFIER:

On my 1963 L-102 I have I have replaced  the R203 4.7M resistor which thins out the bass response with a 10M resistor which is what is used in the M series and the M-100 series organs and also the AO-28 preamps of the -3 series console organs such as the B3, C3 etc, and I have installed a single pole / two position (SPDT) "centre off" switch that allows me to switch between three different bass response settings which are as follows :

Position 1)  The 10M resistor which replaced the R203 4.7M resistor is switched in place thus resulting in the stock sound but with an improved deeper bass response.

Position 2 Middle position "centre off" setting) The 10M resistor is completely switched out of circuit thus resulting in a big boost to the bass frequencies and the lower midrange frequencies.

Position 3)  A 39pFcapacitor is switched in series with the 10M resistor thus resulting in a boost to the bass frequencies.

Wire up a 0.47uF 630V rated capacitor in parallel with the C204 0.047uF capacitor that is wired after the plate of the V1A so that the lowest bass frequencies will fully pass through without becoming attenuated by the subsequent circuitry in the signal path.

WHAT TO DO:

  • Replace the R203 feedback resistor with a 10M resistor.
  • Install a SPDT "centre off" switch that will allow you to switch between three different bass response settings which are as follows :
  • Position 1)  The 10M resistor which replaced the R203 resistor is switched in place thus resulting in the stock sound but with the improved deeper bass response.
  • Position 2 Middle position "centre off " setting) The 10M resistor is completely switched out of circuit thus resulting in a big boost to the bass frequencies and the lower midrange frequencies.
  • Position 3) A 39pF capacitor is switched in series with the 10M resistor thus resulting in a boost to the bass frequencies.
  • Wire up a 0.47uF 630V rated capacitor in parallel with the C204 capacitor to allow the lowest bass frequencies to fully pass through.