Tone Bender MK2 circuit all using NPN BJTs (in reverse darlington) and negative ground. This adds a bit of modifications on the original circuit, to build with my surplus parts in drawer.
1. Changed capacitor values (4.7uF -> 10uF, 47uF -> 100uF)
2. Added extra VR for voltage control (3.7V … 9V)
3. Added extra DPDT (on-off-on) switch for low-pass filter (800Hz/1.6kHz) at volume 50%
