"The third, newest soviet union version of the Small Stone was again a small modification from the previous one. The circuit board layout has been modified and the components arranged a little bit more neatly, propably to ease the assembly of the units. The design still employs the 5 CA3094E OTA chips, so no big change there." (pedalarea.com)
4 STAGE MOD - added toggle switches opens new sound variations
COLOR MOD - "Color" switch is replaced by a pot to have full control over the feedback range, from classic phasing to self-oscillation (Small Stone uses feedback to enhance the peaks in the frequency response)