CV/Gate inputs for the RITM-2 synthesizer

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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.ritm_2_side

Please read the schematics of the RITM-2.

Below is the adapter board schematics.ritm2_cv_gate_schematics

This is the junction points which are need to be connected to adapter. (1, 2, 3) Additional points are for other CV inputs.
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The point 1 (CV OUT) is here, between the R117 and R102.
ritm_2_r_117

Point 2 (SOURCE) is right on the VCA Attack slider pot.
ritm_2_r_173

Point 3 (DRAIN) is right on the VCF Attack slider.
ritm_2_r_175

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.
ritm_2_powerboard

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.
ritm2_cv_gate_layout

This is how assembled board looks like.

ritm_2_cvgate_board
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.