If you're technically competent, or have someone else who is, and can refer them to this page, it lists a few changes that you can make to the organ, if you feel the need.
Pedal voices
I found that the 8′ bass pedal voice was too loud compared against the 16′ flute, and lacking in interesting harmonics. Also, at the top of the pedal board, the 8’ flute is too trebly to be useful as a bass note (so I never use the 8’ pedal flute by itself). Both are derived from square waves, then filtered with simple RC π filters. The 8′ directly from a square wave, filtered down to a crude sinewave. But the 16′ square wave is first ANDed with the 8′ square wave, giving an uneven mark space ratio, so that that the filtered output is more of a complex sawtooth. I modified things in two stages.
Reduce the output level of the 8′ bass flute, individually from the other bass pedal voices: This can be done by inserting a trimpot between C31 and R85 near the chamfered corner of the PTF (pedal tone filter) board. I simply put a 1 MΩ trimpot and 100 kΩ resistor in series between them.
Change the timbre of the 8′ bass flute: I changed the input tone of the 8′ flute from a square wave to a rectangular wave (like the 16′ flute), by isolating pin 1 of IC4 from the circuit board tracks (with a sharp knife), then connecting IC4's pin 1 (AND gate input) directly to IC5's pin 1 (the nearest 4′ square wave signal going to IC5) with a jumper lead. This is on the same PTF board
This makes the 8′ pedal flute a bit better (for me) without too much fiddling with the circuitry, giving it more bass rumble.
Similar level controls could be inserted for the other pedal voices, by inserting 1 or 2 megohm trimpots on the PTF board between capacitors and resistors as listed:
| Voice | between |
|---|---|
| 16′ flute | C26 & R77 |
| 8′ flute | C31 & R85 |
| 16′ tuba | C36 & R92 |
| bass guitar | C41 & R99 |
| string bass | C48 & R106, C51 & R113 |
(The string bass has two output stages {string pluck and bass tone} that are mixed together.)
Later on I did put volume pots on all the above output signals, essentially creating drawbars for each voice (the string bass gets a pot for the pluck effect and another for the bass tone).
I also found that on my organ the bass pedals became too quiet when the pedal celeste effect is on. On some board revisions there's a different value capacitor feeding the pedals to the celeste signal path on the SEL (select) PCB: C17 (1 μF) feeds the straight audio path, C15 (0.033 μF). Older boards had 1 μF for both caps. Try increasing the value of C15, or just tack a 1 μF capacitor across it on the other side of the board. If it's, now, too loud, try a lower cap value. Polarity is marked on the board, both caps have negative facing the same way, and they're both quite close to pin 23 of the edge connector.
I added a pedal out signal from pin 69 of the PTF board (a resistor feeding an audio transformer, giving me a balanced output which is floating from ground). This is pre-expression and pre-pedal-volume put (the one below the pedal tab switches on the stop rail), which suited me fine for my recording purposes (expressive melody volume, but constant bass volume, when collaborating with other musicians).
But if you want post-expression audio, then take a tap from the SEL board, instead, its pin 41 will have the straight (no-celeste) pedal audio (but muted if pedal celeste is switched on), that goes to the RME mixing boad. Alternatively, pin 8 of IC4 is the output of the VCA IC for the pedal signal, it'll always have the straight audio of the pedal signal, whether pedal celeste is switched on or not.