Sorry, but english version of this page is very brief due to large amount of text that need to be translated. Feel free to contact me if you’re interested to modify this brilliant soviet synthesizer and have questions about schematics shown below. Thanks for understanding.
Briefly: This adapter converts standard 1v/oct CV and positive Gate signal to -1.18 v/oct used by synthesizer and s-trig alike switch in parallel to mechanical switch used by keyboard.
This is CV/Gate Inputs. Mounted at the left side. There is a wooden bar inside the synthesizer at the left side. It is useful as place to mount adapter board.
Please read the schematics of the RITM-2.
Below is the adapter board schematics.
The point 1 (CV OUT) is here, between the R117 and R102.
Point 2 (SOURCE) is right on the VCA Attack slider pot.
Point 3 (DRAIN) is right on the VCF Attack slider.
This is a points where you can get power from internal power source. It’s kind of tricky to place these pins to new holes. I used leads from some wire, wrapped it around soldering side of the pins to obtain some kind of surface and soldered it all to nearest PCB track and wire connected thru-hole.
This is stripboard components layout.Please note that component designators from the left side od the OpAmp is shifted by accident. The negative side of the D1 shold be pointed to the Q1. Cut points shown as red crosses.
This is how assembled board looks like.
Additional CV Inputs
4: Audio In. Connect thru 120k resistor. It is high-voltage input! To work with line-level signals, you need to use 10k resistor in serie with “Gain” 100k potentiometer.
5: PWM In. Connect thru 10k resistor. You can try lower values to get wider response. By the way, control knob didn’t allow to use full range. You can reach very narrow pulses with external control.
6: VCF CV In. Connect thru 100k resistor. Input is exponential. You can try to use some trimmers to obtain precise response. The range is about from −2,5v to +2,5v.
7: VCA CV In. Connect thru 33K resistor. Range: 0—5v.