We get questions regularly about our Ring Modulator we use in many of the earlier videos.  The ring modulator that hides in the 131i Synth case is actually an active ring modulator and not a passive ring modulator.  But you can make your passive ring modulator active by adding a switch, a resistor, a potentiometer and our 555 Timer Oscillator Kit to our Passive Ring Modulator.

To make an active ring modulator you’ll need.

• 1k 1/4W Resistor
• 100k Potentiometer (audio preferred but not required)
• SPST switch
• 555 Timer Oscillator
• 9V Battery Clip
• Passive Ring Modulator

1) Build up the 555 Timer Oscillator leaving off the output jack.

2) Assemble the Passive Ring Modulator normally.

3) Add the SPST switch to the battery connector of the 555 Timer circuit. You can best accomplish this by cutting the red lead of the battery connector right in the middle.  Then strip and solder each of the ends of the wire to a post on the SPST switch.  We add this switch to the circuit because when you run the ring mod as passive you’ll want to turn off the 555 Timer to eliminate the noise it can add to the circuit.

4) Add the 1k resistor and 100k potentiometer to the output of the 555 Timer Oscillator as shown in the schematic below. One end of the 1k resistor connects to the output of the 555 Timer oscillator, the other end connects to pin 3 of the potentiometer. The ground side of the 555 Timer oscillator output is connected to pin 1 of the potentiometer.

Mod additions to make an active ring modulator

5) Connect to the passive ring modulator. Connect pin 2 of the potentiometer to the ring connector of the carrier input (Y).  (This should be the unused connection on the carrier Y jack if you assembled the passive ring correctly.) Connect pin 1 of the potentiometer to the sleeve of carrier input (Y). We connect to the ring on the 1/8″ jack since it is shorted to the tip when no plug is inserted. This way, when a plug is inserted into the carrier Y connector the 555 timer output will be disconnected. No mixing of signals, Yay!

There you have it, your passive ring modulator is now active. You have a switch to turn off your 555 timer when not in use, the potentiometer in the 555 timer circuit adjusts frequency of oscillation, and the added potentiometer acts as a level control for the 555 input to your ring modulator.