circuit bending details
The PCB has only one CPU but many discrete components.
Unusual is that the keyboard matrix employs resistors instead of diodes.
additional higher note keys:
The keyboard matrix is divided into groups with each
7 keys. The matrix outputs are CPU pin {9, 10, 11, 8, 7, 5, 6}, the inputs
are pin {12, 13, 14, 15, 16, 17, 18, 19}. The additional higher note keys
are the rightmost 3 of group output 8 and all 7 of output 7. You need a
complex multifold switch to make the additional keys accessible (e.g. to
use more keys for the main voice since there is really no matrix easteregg
feature to switch the chord section to melody voice play). Also
the tuning knob needs adjustment (only possible with increased range?)
to achieve standard tuning after switching the key range.
volume control:
The volume control employs a row of 5 resistors (each
10 kOhm) wired in series and connected to the volume slide switch PCB contacts.
Wire 2.2 kOhm parallel to the first one to make the first step quieter
(or add a potentiometer instead of the row for stepless volume control).
bass volume & distortion:
A 30 kOhm potentiometer across the diode D5 (wiper
to right end, other end open) distorts the bass. For bass volume control
solder another potentiometer with the ends between the input of D5 and
GND, and its wiper through a 39 kOhm resistor to the upper end of resistor
R80.
envelope attack rate:
The electrolytic capacitor C6 controls the envelope
attack rate during monophonic play.
increase pitch range:
The pitch range can be increased by changing some
resistors at the pitch potentiometer (and increasing its value for achieving
lower pitch). When pitch is turned very high by this, the keyboard
responds wrongly due to overclocking problems. Wire 22 kOhm pull-up resistors
at each keyboard input line (at CPU pin 12 to pin
19) against +5V to reduce the problems.
Attention: I have only very incomplete
draft schematics of my modification, thus this description might be partly
inaccurate or even wrong since it is based on them. |
